Abstract

Thermophilic and hyperthermophilic Archaea and Bacteria have been isolated from marine hydrothermal systems, heated sediments, continental solfataras, hot springs, water heaters, and industrial waste. They catalyze a tremendous array of widely varying metabolic processes. As determined in the laboratory, electron donors in thermophilic and hyperthermophilic microbial redox reactions include H2, Fe2+, H2S, S, S2O32−, S4O62−, sulfide minerals, CH4, various mono-, di-, and hydroxy-carboxylic acids, alcohols, amino acids, and complex organic substrates; electron acceptors include O2, Fe3+, CO2, CO, NO3, NO2, NO, N2O, SO42−, SO32−, S2O32−, and S. Although many assimilatory and dissimilatory metabolic reactions have been identified for these groups of microorganisms, little attention has been paid to the energetics of these reactions. In this review, standard molal Gibbs free energies (ΔGr°) as a function of temperature to 200°C are tabulated for 370 organic and inorganic redox, disproportionation, dissociation, hydrolysis, and solubility reactions directly or indirectly involved in microbial metabolism. To calculate values of ΔGr° for these and countless other reactions, the apparent standard molal Gibbs free energies of formation (ΔG°) at temperatures to 200°C are given for 307 solids, liquids, gases, and aqueous solutes. It is shown that values of ΔGr° for many microbially mediated reactions are highly temperature dependent, and that adopting values determined at 25°C for systems at elevated temperatures introduces significant and unnecessary errors. The metabolic processes considered here involve compounds that belong to the following chemical systems: H–O, H–O–N, H–O–S, H–O–N–S, H–O–Cinorganic, H–O–C, H–O–N–C, H–O–S–C, H–O–N–S–Camino acids, H–O–S–C–metals/minerals, and H–O–P. For four metabolic reactions of particular interest in thermophily and hyperthermophily (knallgas reaction, anaerobic sulfur and nitrate reduction, and autotrophic methanogenesis), values of the overall Gibbs free energy (ΔGr) as a function of temperature are calculated for a wide range of chemical compositions likely to be present in near-surface and deep hydrothermal and geothermal systems.

Introduction

In the late 1970s, with the discovery of the Archaea, Woese and coworkers rang in the most recent biological revolution by proposing that gene sequences could be used to divide all life on Earth into three distinct groups which are taxonomically above the level of kingdom. These groups later became known as domains and include the Eucarya, Bacteria (formerly Eubacteria), and Archaea (formerly Archaebacteria) [1]. Partial ribosomal RNA sequences from countless organisms have now been determined and employed to establish phylogenetic relationships. In addition, approximately 30 complete genomes, including those of several Archaea, have been deciphered, and having as many as 100 microbial genomes in the very near future no longer seems unrealistic [2]. Although phylogenetic trees built upon this ever-increasing wealth of partial and complete genomic data may differ, in some cases significantly [3], these data provide the cornerstone for investigating life’s phylogenetic diversity, the Earth’s evolutionary history, and the universal ancestor [4].

Beyond genetic relations, molecular phylogeny can also be used to interpret the evolutionary progression of metabolic and consequently microbial diversity [5]. A striking feature of global phylogenetic trees that cannot be overlooked is that thermophiles, organisms that favor elevated temperatures, represent the deepest and shortest branches of these trees, both in the Bacteria and particularly the Archaea domains. It follows that the origin and evolution of many metabolic reactions and pathways may be rooted in thermophiles. At the same time, discoveries about thermophiles are continuously being made and many reactions known only from mesophiles at present may also be conducted by unknown thermophiles.

Perhaps the most fundamental characteristic dictating the progression of a metabolic reaction, in fact any chemical reaction, is the amount of energy required or released. A quantitative assessment of the energy budget at the appropriate temperature, pressure, and chemical composition of the system of interest is an essential prerequisite for determining which of a large array of metabolic reactions may be energy-yielding (exergonic). Energy conservation in microorganisms living at ambient conditions (mesophiles) is well documented [6], but the counterpart for organisms at elevated temperatures is not. The purpose of this study is to calculate the energetics as a function of temperature and pressure for numerous known metabolic reactions and determine which of these may provide an energetic drive for thermophilic microorganisms. For reasons discussed below, the emphasis is placed on overall metabolic reactions rather than the stepwise reactions which constitute assimilatory processes. These overall reactions, such as the reduction of elemental sulfur by H2 to yield H2S, or the oxidation of methane (CH4) by O2 to yield CO2 and H2O, generally consist of several electron transfer steps, each of which may be catalyzed by a different enzyme. Therefore, the organism containing the appropriate enzymes is viewed as mediating the sum of stepwise reactions in overall metabolic processes.

Thermophiles and hyperthermophiles

Life at high temperature

An alkaline hot spring in the Lower Geyser Basin of Yellowstone National Park, USA hosts Thermocrinis ruber, an aerobic, facultatively chemolithotrophic Bacterium that grows in the laboratory between 44 and 89°C by oxidizing hydrogen, elemental sulfur, thiosulfate, formate, or formamide. Deep-sea hydrothermal systems at a depth of 2600 m near 21°N on the East Pacific Rise support anaerobic autotrophic methanogens such as Methanococcus jannaschii which grows optimally in the laboratory at ∼85°C. Meanwhile, acid solutions generated by the interaction of volcanic gases and seawater at Vulcano in the Aeolian Islands and the solfatara fields of Naples, Italy are the habitats of acidophilic Archaea, including Acidianus infernus, Thermoplasma volcanium, and Metallosphaera sedula, which grow optimally at a pH near 2. The enormous genetic and metabolic diversity present in high temperature environments reflect the ranges of pH, oxidation/reduction states, solute concentrations, gas compositions, and mineralogy that characterize these environments.

Microorganisms which inhabit these high temperature environments are defined as thermophilic if their optimum growth temperatures are >45°C [7]. If an organism has optimum and maximum growth temperatures of at least 80 and 90°C, respectively, it is further defined as a hyperthermophile [8]. The current maximum growth temperature of a pure isolate is 113°C [9], but microbiologists are willing to speculate that the upper temperature limit for life may be closer to 150°C [10, 11]. Circumstantial evidence obtained from mixed culture experiments [12], particulate DNA concentrations in black smoker fluids [13, 14], direct cell counts on sediment samples [15], and fluid inclusion studies [16] suggests that even this estimate appears conservative. Regardless of what the maximum growth temperature of life on Earth may be – if such a temperature does in fact exist – it is safe to say that it remains unknown.

Although extreme temperatures attract considerable attention in the discussion of hyperthermophiles [10, 11], biomolecule stability [17–20], and the universal ancestor [21–23], they are less relevant than the availability of energy. All chemosynthetic organisms gain energy by catalyzing oxidation/reduction (redox) reactions that are slow to equilibrate on their own. These reactions have to be thermodynamically favored but kinetically inhibited to serve as energy sources. As temperature increases, reaction rates also increase, and at some elevated temperature, abiotic reaction rates are so fast that there is no benefit to an organism if it catalyzes the reaction. Therefore, at high temperatures, it is the rapid unassisted approach to equilibrium that places a limit on life and not temperature itself.

Natural host environments

Easily accessible natural biotopes of thermophilic microbes include shallow and deep marine hydrothermal vent environments, heated beach sediments, continental solfataric areas, and hot springs. The in situ temperatures and pressures of these habitats vary considerably, but more than cover the range to which known organisms have adapted. The majority of these systems are characterized by extremely low oxygen concentrations. Consequently, most of the known species of thermophiles are classified as obligate or facultative anaerobes, though aerobic and microaerophilic isolates are also known. As noted by Brock [24], the majority of continental hot spring fluids exhibit a bimodal distribution with respect to pH with average values either in the acidic region (pH 1–3) or near neutral to slightly alkaline (pH 7–9). It should thus come as no surprise that a preponderance of thermophiles is either acidophilic or neutrophilic.

Although many thermophile biotopes have in situ pressures significantly greater than atmospheric, researchers are only starting to realize the effects of pressure on cell growth. For example, the survival of the deep-sea hyperthermophile Pyrococcus strain ES4 at super-optimal temperatures was enhanced by elevated pressure (220 bar) relative to low pressure (30 bar) [25]. On the other hand, the hyperthermophile Pyrolobus fumarii isolated from a depth of 3650 m from a hydrothermally heated black smoker fragment at the Mid Atlantic Ridge showed no growth enhancement when incubated at 250 bar relative to experiments at 3 bar [9]. In contrast, earlier experiments on M. jannaschii, an autotrophic methanogen from submarine hydrothermal systems, showed a decrease in doubling time from 83 min at 86°C and 7.8 bar to 18 min at the same temperature but 750 bar [26]. At 90°C, in the same study, the doubling time of M. jannaschii decreased from 160 min at 7.8 bar to 50 min at 750 bar. Owing to the wide range of temperature, pressure, fluid chemistry, and mineralogy of host environments, the metabolic strategies of thermophiles are, accordingly, highly diverse.

Deep biosphere

It is increasingly apparent that surface thermal features and the organisms they support are giving researchers a glimpse of what life may be like in the deep subsurface [27, 28]. Indeed, numerous studies have shown that a subsurface biosphere exists in coastal plain sediments, sedimentary basins, and granitic and basaltic aquifers (see Table 1). For example, autotrophic methanogens and SO42− and Fe3+ reducers have been identified at depths up to 1300 m in basaltic rock in Washington, USA [29, 30]. In addition, sedimentary rocks, such as sandstone, shale, and limestone at depths up to 3200 m and temperatures >80°C are hosts to a variety of autotrophs and heterotrophs, including aerobes and SO42−, S, Fe3+, Mn4+, and NO3 reducers [31, 32]. In the granitic aquifers at Gravberg, Sweden, heterotrophic metabolism has been documented at a depth of 3500 m at 60°C [33, 34]. Furthermore, thermophiles and hyperthermophiles have been cultured at temperatures up to ∼100°C from oil field waters in the Paris Basin and the North Sea [35–38], and obligate and facultative barophiles (organisms that favor elevated pressures) thrive in marine sediments hundreds of meters below the sediment–water interface [28, 39].

Table 1

Direct observations of microorganisms in the deep subsurface

Location Rock or fluid type Max. depth (m) TMAX (°C) Laboratory metabolism References 
Cerro Negro, NM, USA Sandstone, shale 247  Heterotrophy, SO42− reduction, acetogenesis [163] 
Savannah River, Aiken, SC, USA Sediments of sand and clay 260  Aerobic and anaerobic heterotrophy, SO42− reduction, methanogenesis, nitrification, N2-fixation [164, 165
Rainier Mesa, NV, USA Volcanic ashfall tuff 400 18 Aerobic chemoheterotrophy [166, 167
Lac du Bonnet batholith, Man., Canada Granite 420  Fe3+ and SO42− reduction, Fe2+ oxidation [168, 169
Japan Sea, Peru Margin, Eastern equatorial Pacific, Juan de Fuca Ridge, Lau Basin, Philippine Trench, Kermadec-Tonga Trench, Soenda Deep, Weber Deep Marine sediments 518a 80 SO42−-reducing methanotrophyb, NO3 and SO42− reduction, obligate and facultative barophily [28, 39
Äspö, Sweden Granite 860 20.5 Heterotrophic Fe3+ and SO42− reduction, autotrophic methanogenesis and acetogenesis [40–43
Great Artesian Basin, Australia Thermal aquifer 914 88 Heterotrophic and autotrophic SO42− reduction [170–172
Stripa mine, Sweden Granite 1240 26 Heterotrophy and autotrophy [173] 
Hanford Reservation, Washington, USA Basalt 1300  Autotrophic methanogenesis, SO42− and Fe3+ reduction [29, 30
Madison Formation, MT, USA Aquifers in dolomitic limestone 1800 50 SO42− reduction, methanogenesis [174] 
Piceance Basin, CO, USA Sandstone and shale 2100 85 Heterotrophic and autotrophic Fe3+ reduction [175, 176
Paris Basin, France Oil field brine, geothermal water 2500 85 Heterotrophic and autotrophic SO42− reduction, autotrophic methanogenesis [35, 38, 177, 178
Taylorsville Basin, VA, USA Siltstone and shale 2800 85 Heterotrophic SO42− and Fe3+ reduction [175, 179
Witwatersrand, South Africa Carbonate, sandstone, shale 3200 60 Heterotrophic Fe3+, Mn4+, S, NO3, O2 reduction [31, 32, 173
Gravberg, Siljan Ring, Sweden Granite 3500 60 Heterotrophy [33, 34
Northsea oil fields: Statfjord and Beatrice fields, East Shetland basin Oil field waters 4000 110 Heterotrophic SO42−, SO32−, S2O32−, and S reduction, autotrophic SO42− reduction, Heterotrophic Mn4+, Fe3+, and NO3 reduction [36, 37, 180, 181
Location Rock or fluid type Max. depth (m) TMAX (°C) Laboratory metabolism References 
Cerro Negro, NM, USA Sandstone, shale 247  Heterotrophy, SO42− reduction, acetogenesis [163] 
Savannah River, Aiken, SC, USA Sediments of sand and clay 260  Aerobic and anaerobic heterotrophy, SO42− reduction, methanogenesis, nitrification, N2-fixation [164, 165
Rainier Mesa, NV, USA Volcanic ashfall tuff 400 18 Aerobic chemoheterotrophy [166, 167
Lac du Bonnet batholith, Man., Canada Granite 420  Fe3+ and SO42− reduction, Fe2+ oxidation [168, 169
Japan Sea, Peru Margin, Eastern equatorial Pacific, Juan de Fuca Ridge, Lau Basin, Philippine Trench, Kermadec-Tonga Trench, Soenda Deep, Weber Deep Marine sediments 518a 80 SO42−-reducing methanotrophyb, NO3 and SO42− reduction, obligate and facultative barophily [28, 39
Äspö, Sweden Granite 860 20.5 Heterotrophic Fe3+ and SO42− reduction, autotrophic methanogenesis and acetogenesis [40–43
Great Artesian Basin, Australia Thermal aquifer 914 88 Heterotrophic and autotrophic SO42− reduction [170–172
Stripa mine, Sweden Granite 1240 26 Heterotrophy and autotrophy [173] 
Hanford Reservation, Washington, USA Basalt 1300  Autotrophic methanogenesis, SO42− and Fe3+ reduction [29, 30
Madison Formation, MT, USA Aquifers in dolomitic limestone 1800 50 SO42− reduction, methanogenesis [174] 
Piceance Basin, CO, USA Sandstone and shale 2100 85 Heterotrophic and autotrophic Fe3+ reduction [175, 176
Paris Basin, France Oil field brine, geothermal water 2500 85 Heterotrophic and autotrophic SO42− reduction, autotrophic methanogenesis [35, 38, 177, 178
Taylorsville Basin, VA, USA Siltstone and shale 2800 85 Heterotrophic SO42− and Fe3+ reduction [175, 179
Witwatersrand, South Africa Carbonate, sandstone, shale 3200 60 Heterotrophic Fe3+, Mn4+, S, NO3, O2 reduction [31, 32, 173
Gravberg, Siljan Ring, Sweden Granite 3500 60 Heterotrophy [33, 34
Northsea oil fields: Statfjord and Beatrice fields, East Shetland basin Oil field waters 4000 110 Heterotrophic SO42−, SO32−, S2O32−, and S reduction, autotrophic SO42− reduction, Heterotrophic Mn4+, Fe3+, and NO3 reduction [36, 37, 180, 181

aThis refers to the depth below the sediment–water interface, not the depth below sea level.

bAlthough methanotrophs able to use SO42− as their electron acceptor have not been isolated, other lines of evidence strongly suggest their existence.

The metabolic diversity already examined in the deep biosphere shows that chemosynthetic organisms can take advantage of many forms of energy that are sufficient to support life [40–43]. These energy sources can be linked to photosynthesis at the surface, as in the case of heterotrophs that use organic compounds in sediments that are the residue of photosynthetic organisms, or they can be completely independent of photosynthesis, as in the case of autotrophs that gain energy and fix carbon by reacting CO2 and H2 provided by geologic processes [30, 44, 45]. These observations lead inescapably to the proposition that microorganisms can live in the subsurface wherever there are sources of geochemical energy and where the system is open to mass exchange on at least the timescale of microbial processes.

Metabolism of thermophiles and hyperthermophiles

Energy-yielding substrates for autotrophs and heterotrophs

More than 200 species of thermophiles and hyperthermophiles belonging to circa 100 genera (Table 2) are currently known. These microorganisms can carry out a wide variety of metabolic processes featuring a multitude of electron donors and acceptors. To date, 12 genera are known within the Archaea, both aerobes and anaerobes, autotrophs as well as heterotrophs, which catalyze metabolic reactions at temperatures ≥100°C. Although the metabolic pathways used by thermophiles and hyperthermophiles are still largely unresolved, several dominant characteristics of energy-yielding redox reactions are apparent. Only approximately 25 known genera of thermophiles and hyperthermophiles contain obligate aerobes; most are obligate anaerobes, but some are facultative anaerobes. Therefore, the common electron acceptors used by these organisms include, for example, sulfate, nitrate, carbon dioxide, and ferric iron rather than oxygen. This directly reflects the geochemical nature of the biotopes discussed above.

Table 2

Taxonomy and metabolic features of thermophiles and hyperthermophiles

Genus Species TMAX (°C) Hetero/auto Aerobe/anaerobe References 
Thermophilic Bacteria 
Acidimicrobium ferrooxidans 57 FA FAN [182, 183
Alicyclobacillus acidocaldarius 70 AE [184–186
 acidoterrestris 60 AE [184] 
 cycloheptanicus 53 AE [184] 
Ammonifex degensii 77 FA AN [187] 
Anaerobranca horikoshii 66 AN [188] 
Bacillus infernus 61 AN [116] 
 schlegelii 79 FA AE [189] 
 thermoantarcticus 65 AE [190, 191
 thermoleovorans 78 FAN [192] 
 thermosphaericus 64 AE [193] 
 tusciae 55a FA AE [194] 
Calderobacterium hydrogenophilum 82 AE [195] 
Caldicellulosiruptor lactoaceticus 78 AN [196] 
 owensensis 80 AN [197] 
 saccharolyticus 80 AN [198] 
Caloramator indicus 75 AN [199] 
 proteoclasticus 68 AN [200] 
Chloroflexus aurantiacus 65 FAN [201] 
Clostridium paradoxim 63 AN [202] 
 thermosuccinogenes 65 AN [203] 
Coprothermobacter proteolyticus 75 AN [204] 
Deferribacter thermophilus 65 AN [181] 
Deinococcus geothermalis 55 AE [205] 
 murrayi 52 AE [205] 
Desulfacinum infernum 65 FA AN [206] 
Desulfotomaculum australicum 74 FA AN [170] 
 geothermicum 57 FA AN [35] 
 kuznetsovi 85 FA AN [207] 
 luciae 70 FA AN [175, 208
 nigrificans ssp. salinus 70 AN [209] 
 putei 65 FA AN [175] 
 thermoacetoxidans 65 FA AN [210] 
 thermobenzoicum 70 AN [211] 
 thermocisternum 75 FA AN [180] 
 thermosapovorans 60 FA AN [212] 
Desulfurella acetivorans 70 AN [213] 
 kamchatkensis 70 FA AN [214] 
 multipotens 77 FA AN [215] 
 propionica 63 FA AN [214] 
Desulfurobacterium thermolithotrophum 75 AN [216] 
Dictyoglomus turgidus 86 AN [217] 
Fervidobacterium islandicum 80 AN [218] 
 nodosum 79 AN [219] 
 pennavorans 80 AN [220] 
Flexistipes sinusarabici 53 AN [221] 
Geotoga petraea 55 AN [222] 
 subterranea 60 AN [222] 
Halothermothrix orenii 68 AN [223] 
Hydrogenobacter acidophilus 65 AE [224] 
 halophilus 75 AE [225] 
 thermophilus 79 AE [226, 227
Hydrogenophilus thermoluteolus 52 FA AE [228, 229
Isosphaera pallida 55 AE [230] 
Meiothermus cerbereus 60 AE [231] 
 chliarophilus 60 AE [232] 
 ruber 65 AE [232] 
 silvanus 65 AE [232] 
Methylococcus thermophilus 62 AE [233] 
Moorella glycerini 65 AN [234] 
 thermoaceticum 65 AN [235, 236
Petrotoga miotherma 65 AN [222] 
 mobilis 65 AN [237] 
Rhodothermus marinus 77 AE [238] 
 obamesis 85 AE [239] 
Rubrobacter xylanophilus 70 AE [240] 
 radiotolerans 48a AE [241] 
Sphaerobacter thermophilus 60 AE [242] 
Spirochaeta caldaria 52a AN [243] 
 thermophila 73 AN [244] 
Sulfobacillus acidophilus 50 FA FAN [183, 245
 thermosulfidooxidans 55 FA FAN [183, 246, 247
Thermaerobacter marianensis 80 AE [248] 
Thermoanaerobacter acetoethylicus 79 AN [204, 249
 brockii 85 AN [250–252
 ethanolicus 78 AN [252, 253
 kivui 72 FA AN [236, 254
 mathranii 75 AN [255] 
 sulfurophilus 75 AN [256] 
 thermohydrosulfuricus 78 AN [252] 
 wiegelii 78 AN [257] 
Thermoanaerobacterium aotearoense 66 AN [258] 
 saccharolyticum 70 AN [252] 
 thermosulfurigenes 75 AN [252] 
 xylanolyticum 70 AN [252] 
Thermoanaerobium lactoethylicum 75 AN [259] 
Thermobrachium celere 75 AN [260] 
Thermocrinis ruber 89 FA AE [261] 
Thermocrispum agreste 62 AE [262] 
 municipale 62 AE [262] 
Thermodesulfobacterium commune 85 AN [263] 
 mobile 85 AN [264, 265
Thermodesulforhabdus norvegicus 74 AN [266] 
Thermodesulfovibrio yellowstonii 70 AN [267] 
Thermohalobacter berrensis 65 AN [268] 
Thermohydrogenium kirishiense 75 AN [269] 
Thermoleophilum album 70 AE [270] 
Thermomicrobium roseum 85 AE [271] 
Thermonema rossianum 65 AE [272] 
Thermosipho africanus 77 AN [273] 
Thermosyntropha lipolytica 70 AN [274] 
Thermoterrabacterium ferrireducens 74 AN [275] 
Thermothrix azorensis 87 AE [276] 
 thioparus 77 FA FAN [277, 278
Thermotoga elfii 72 AN [279] 
 hypogea 90 AN [280] 
 subterranea 75 AN [281] 
 thermarum 84 AN [282] 
Thermus aquaticus 79 AE [283] 
 oshimai 70 AE [284] 
 thermophilus 85 AE [285] 
Thiobacillus thermophilica 80 AE [286] 
Hyperthermophilic Bacteria 
Aquifex pyrophilus 95 FAN [82] 
Thermotoga maritima 90 AN [287] 
 neapolitana 90 AN [288] 
Thermophilic Archaea 
Acidianus ambivalens 87 FAN [289–291
 brierleyi 75 FA FAN [292–294
Archaeoglobus lithotrophicus 89 AN [37] 
 veneficus 85 FA AN [295] 
Metallosphaera prunae 80 FA AE [296] 
 sedula 80 FA AE [293, 297
Methanobacterium defluvii 65 AN [298] 
 thermoaggregans 75 AN [299] 
 thermoalcaliphilum 69 AN [300] 
 thermophilum 57 AN [301] 
 thermoflexum 70 AN [298] 
Methanococcus thermolithotrophicus 70 AN [302] 
 vulcanius 89 AN [303] 
Methanoculleus thermophilicum 60 AN [304] 
Methanohalobium evestigatus 60 AN [305] 
Methanosarcina thermophila 50 AN [128] 
Methanothermobacter thermoautotrophicus 75 AN [306] 
 wolfeii 74 AN [307] 
Methanothrix thermophila 60a AN [308] 
Palaeococcus ferrophilus 88 AN [309] 
Picrophilus oshimae 65 AE [310, 311
 torridus 65 AE [310, 311
Stygiolobus azoricus 89 AN [312] 
Sulfolobus acidocaldarius 80 FA FAN [293, 313–315
 hakonensis 80 FA AE [316] 
 metallicus 75 AE [317] 
 shibatae 86 FA AE [293, 318, 319
 solfataricus 87 FA AE [293, 320
Sulfurococcus mirabilis 86 FA AE [321] 
 yellowstonii 80 FA AE [322] 
Thermocladium modestius 82 FAN [259] 
Thermococcus zilligii 85 AN [323, 324
Thermoplasma acidophilum 63 FAN [325, 326
 volcanium 67 FAN [325] 
Hyperthermophilic Archaea 
Acidianus infernus 96 FAN [292, 293
Aeropyrum pernix 100 AE [327] 
Archaeoglobus fulgidus 95 FA AN [328–330
 profundus 90 AN [331] 
Caldivirga maquilingensis 92 FAN [332] 
Caldococcus litoralis 100 AN [333] 
 noboribetus 96 AN [334, 335
Desulfurococcus amylolyticus 97 AN [336] 
 mobilis 97 AN [337] 
 mucosus 97 AN [337] 
Ferroglobus placidus 95 FA AN [84] 
Hyperthermus butylicus 108 AN [338] 
Methanococcus fervens 92 AN [303, 339
 igneus 91 AN [340] 
 infernus 91 AN [341] 
 jannaschii 94 AN [126, 304
Methanopyrus kandleri 110 AN [94, 342
Methanothermus fervidus 97 AN [343] 
 sociabilis 97 AN [344] 
Pyrobaculum aerophilum 104 FA FAN [345] 
 islandicum 102 FA AN [346] 
 organotrophum 102 AN [346] 
Pyrococcus abyssi 108 AN [347] 
 endeavori (ES4) 110 AN [348] 
 furiosus 103 AN [349] 
 horikoshii 102 AN [350] 
 woesei 104 AN [351] 
Pyrodictium abyssi 110 AN [347] 
 brockii 110 AN [352, 353
 occultum 110 AN [352, 353
Pyrolobus fumarii 113 FAN [9] 
Staphylothermus marinus 98 AN [354] 
Stetteria hydrogenophila 102 AN [355] 
Sulfophobococcus zilligii 95 AN [356] 
Sulfurisphaera ohwakuensis 92 FAN [357] 
Thermococcus acidaminovorans 93 AN [358] 
 aggregans 94 AN [359] 
 alcaliphilus 90 AN [360] 
 barophilus 100 AN [361] 
 barossi 92 AN [362] 
 celer 93 AN [363] 
 chitonophagus 93 AN [364] 
 fumicolans 103 AN [365] 
 gorgonarius 95 AN [366] 
 guaymasensis 90 AN [359] 
 hydrothermalis 100 AN [367] 
 litoralis 98 AN [368, 369
 pacificus 95 AN [366] 
 peptonophilus 100 AN [370] 
 profundus 90 AN [371] 
 siculi 93 AN [372] 
 stetterib 98 AN [373] 
Thermodiscus maritimus 98 H/Ac AN [374, 375
Thermofilum pendens 100 AN [376] 
Thermoproteus neutrophilus 85a AN [375] 
 tenax 96 FA AN [375, 377
 uzoniensis 102 AN [378] 
Thermosphaera aggregans 90 AN [261] 
A: autotroph; H: heterotroph; FA: facultative autotroph (or facultative heterotroph); AN: anaerobe; AE: aerobe; FAN: facultative anaerobe (or facultative aerobe). 
Genus Species TMAX (°C) Hetero/auto Aerobe/anaerobe References 
Thermophilic Bacteria 
Acidimicrobium ferrooxidans 57 FA FAN [182, 183
Alicyclobacillus acidocaldarius 70 AE [184–186
 acidoterrestris 60 AE [184] 
 cycloheptanicus 53 AE [184] 
Ammonifex degensii 77 FA AN [187] 
Anaerobranca horikoshii 66 AN [188] 
Bacillus infernus 61 AN [116] 
 schlegelii 79 FA AE [189] 
 thermoantarcticus 65 AE [190, 191
 thermoleovorans 78 FAN [192] 
 thermosphaericus 64 AE [193] 
 tusciae 55a FA AE [194] 
Calderobacterium hydrogenophilum 82 AE [195] 
Caldicellulosiruptor lactoaceticus 78 AN [196] 
 owensensis 80 AN [197] 
 saccharolyticus 80 AN [198] 
Caloramator indicus 75 AN [199] 
 proteoclasticus 68 AN [200] 
Chloroflexus aurantiacus 65 FAN [201] 
Clostridium paradoxim 63 AN [202] 
 thermosuccinogenes 65 AN [203] 
Coprothermobacter proteolyticus 75 AN [204] 
Deferribacter thermophilus 65 AN [181] 
Deinococcus geothermalis 55 AE [205] 
 murrayi 52 AE [205] 
Desulfacinum infernum 65 FA AN [206] 
Desulfotomaculum australicum 74 FA AN [170] 
 geothermicum 57 FA AN [35] 
 kuznetsovi 85 FA AN [207] 
 luciae 70 FA AN [175, 208
 nigrificans ssp. salinus 70 AN [209] 
 putei 65 FA AN [175] 
 thermoacetoxidans 65 FA AN [210] 
 thermobenzoicum 70 AN [211] 
 thermocisternum 75 FA AN [180] 
 thermosapovorans 60 FA AN [212] 
Desulfurella acetivorans 70 AN [213] 
 kamchatkensis 70 FA AN [214] 
 multipotens 77 FA AN [215] 
 propionica 63 FA AN [214] 
Desulfurobacterium thermolithotrophum 75 AN [216] 
Dictyoglomus turgidus 86 AN [217] 
Fervidobacterium islandicum 80 AN [218] 
 nodosum 79 AN [219] 
 pennavorans 80 AN [220] 
Flexistipes sinusarabici 53 AN [221] 
Geotoga petraea 55 AN [222] 
 subterranea 60 AN [222] 
Halothermothrix orenii 68 AN [223] 
Hydrogenobacter acidophilus 65 AE [224] 
 halophilus 75 AE [225] 
 thermophilus 79 AE [226, 227
Hydrogenophilus thermoluteolus 52 FA AE [228, 229
Isosphaera pallida 55 AE [230] 
Meiothermus cerbereus 60 AE [231] 
 chliarophilus 60 AE [232] 
 ruber 65 AE [232] 
 silvanus 65 AE [232] 
Methylococcus thermophilus 62 AE [233] 
Moorella glycerini 65 AN [234] 
 thermoaceticum 65 AN [235, 236
Petrotoga miotherma 65 AN [222] 
 mobilis 65 AN [237] 
Rhodothermus marinus 77 AE [238] 
 obamesis 85 AE [239] 
Rubrobacter xylanophilus 70 AE [240] 
 radiotolerans 48a AE [241] 
Sphaerobacter thermophilus 60 AE [242] 
Spirochaeta caldaria 52a AN [243] 
 thermophila 73 AN [244] 
Sulfobacillus acidophilus 50 FA FAN [183, 245
 thermosulfidooxidans 55 FA FAN [183, 246, 247
Thermaerobacter marianensis 80 AE [248] 
Thermoanaerobacter acetoethylicus 79 AN [204, 249
 brockii 85 AN [250–252
 ethanolicus 78 AN [252, 253
 kivui 72 FA AN [236, 254
 mathranii 75 AN [255] 
 sulfurophilus 75 AN [256] 
 thermohydrosulfuricus 78 AN [252] 
 wiegelii 78 AN [257] 
Thermoanaerobacterium aotearoense 66 AN [258] 
 saccharolyticum 70 AN [252] 
 thermosulfurigenes 75 AN [252] 
 xylanolyticum 70 AN [252] 
Thermoanaerobium lactoethylicum 75 AN [259] 
Thermobrachium celere 75 AN [260] 
Thermocrinis ruber 89 FA AE [261] 
Thermocrispum agreste 62 AE [262] 
 municipale 62 AE [262] 
Thermodesulfobacterium commune 85 AN [263] 
 mobile 85 AN [264, 265
Thermodesulforhabdus norvegicus 74 AN [266] 
Thermodesulfovibrio yellowstonii 70 AN [267] 
Thermohalobacter berrensis 65 AN [268] 
Thermohydrogenium kirishiense 75 AN [269] 
Thermoleophilum album 70 AE [270] 
Thermomicrobium roseum 85 AE [271] 
Thermonema rossianum 65 AE [272] 
Thermosipho africanus 77 AN [273] 
Thermosyntropha lipolytica 70 AN [274] 
Thermoterrabacterium ferrireducens 74 AN [275] 
Thermothrix azorensis 87 AE [276] 
 thioparus 77 FA FAN [277, 278
Thermotoga elfii 72 AN [279] 
 hypogea 90 AN [280] 
 subterranea 75 AN [281] 
 thermarum 84 AN [282] 
Thermus aquaticus 79 AE [283] 
 oshimai 70 AE [284] 
 thermophilus 85 AE [285] 
Thiobacillus thermophilica 80 AE [286] 
Hyperthermophilic Bacteria 
Aquifex pyrophilus 95 FAN [82] 
Thermotoga maritima 90 AN [287] 
 neapolitana 90 AN [288] 
Thermophilic Archaea 
Acidianus ambivalens 87 FAN [289–291
 brierleyi 75 FA FAN [292–294
Archaeoglobus lithotrophicus 89 AN [37] 
 veneficus 85 FA AN [295] 
Metallosphaera prunae 80 FA AE [296] 
 sedula 80 FA AE [293, 297
Methanobacterium defluvii 65 AN [298] 
 thermoaggregans 75 AN [299] 
 thermoalcaliphilum 69 AN [300] 
 thermophilum 57 AN [301] 
 thermoflexum 70 AN [298] 
Methanococcus thermolithotrophicus 70 AN [302] 
 vulcanius 89 AN [303] 
Methanoculleus thermophilicum 60 AN [304] 
Methanohalobium evestigatus 60 AN [305] 
Methanosarcina thermophila 50 AN [128] 
Methanothermobacter thermoautotrophicus 75 AN [306] 
 wolfeii 74 AN [307] 
Methanothrix thermophila 60a AN [308] 
Palaeococcus ferrophilus 88 AN [309] 
Picrophilus oshimae 65 AE [310, 311
 torridus 65 AE [310, 311
Stygiolobus azoricus 89 AN [312] 
Sulfolobus acidocaldarius 80 FA FAN [293, 313–315
 hakonensis 80 FA AE [316] 
 metallicus 75 AE [317] 
 shibatae 86 FA AE [293, 318, 319
 solfataricus 87 FA AE [293, 320
Sulfurococcus mirabilis 86 FA AE [321] 
 yellowstonii 80 FA AE [322] 
Thermocladium modestius 82 FAN [259] 
Thermococcus zilligii 85 AN [323, 324
Thermoplasma acidophilum 63 FAN [325, 326
 volcanium 67 FAN [325] 
Hyperthermophilic Archaea 
Acidianus infernus 96 FAN [292, 293
Aeropyrum pernix 100 AE [327] 
Archaeoglobus fulgidus 95 FA AN [328–330
 profundus 90 AN [331] 
Caldivirga maquilingensis 92 FAN [332] 
Caldococcus litoralis 100 AN [333] 
 noboribetus 96 AN [334, 335
Desulfurococcus amylolyticus 97 AN [336] 
 mobilis 97 AN [337] 
 mucosus 97 AN [337] 
Ferroglobus placidus 95 FA AN [84] 
Hyperthermus butylicus 108 AN [338] 
Methanococcus fervens 92 AN [303, 339
 igneus 91 AN [340] 
 infernus 91 AN [341] 
 jannaschii 94 AN [126, 304
Methanopyrus kandleri 110 AN [94, 342
Methanothermus fervidus 97 AN [343] 
 sociabilis 97 AN [344] 
Pyrobaculum aerophilum 104 FA FAN [345] 
 islandicum 102 FA AN [346] 
 organotrophum 102 AN [346] 
Pyrococcus abyssi 108 AN [347] 
 endeavori (ES4) 110 AN [348] 
 furiosus 103 AN [349] 
 horikoshii 102 AN [350] 
 woesei 104 AN [351] 
Pyrodictium abyssi 110 AN [347] 
 brockii 110 AN [352, 353
 occultum 110 AN [352, 353
Pyrolobus fumarii 113 FAN [9] 
Staphylothermus marinus 98 AN [354] 
Stetteria hydrogenophila 102 AN [355] 
Sulfophobococcus zilligii 95 AN [356] 
Sulfurisphaera ohwakuensis 92 FAN [357] 
Thermococcus acidaminovorans 93 AN [358] 
 aggregans 94 AN [359] 
 alcaliphilus 90 AN [360] 
 barophilus 100 AN [361] 
 barossi 92 AN [362] 
 celer 93 AN [363] 
 chitonophagus 93 AN [364] 
 fumicolans 103 AN [365] 
 gorgonarius 95 AN [366] 
 guaymasensis 90 AN [359] 
 hydrothermalis 100 AN [367] 
 litoralis 98 AN [368, 369
 pacificus 95 AN [366] 
 peptonophilus 100 AN [370] 
 profundus 90 AN [371] 
 siculi 93 AN [372] 
 stetterib 98 AN [373] 
Thermodiscus maritimus 98 H/Ac AN [374, 375
Thermofilum pendens 100 AN [376] 
Thermoproteus neutrophilus 85a AN [375] 
 tenax 96 FA AN [375, 377
 uzoniensis 102 AN [378] 
Thermosphaera aggregans 90 AN [261] 
A: autotroph; H: heterotroph; FA: facultative autotroph (or facultative heterotroph); AN: anaerobe; AE: aerobe; FAN: facultative anaerobe (or facultative aerobe). 

aThis represents the optimum growth temperature; the maximum growth temperature is not given.

bSome strains are thermophilic with a temperature optimum of 73–77°C and a maximum of 94°C, but others are hyperthermophilic with optimum and maximum growth temperatures equal to 88 and 98°C, respectively [373].

cFischer et al. (1983) [375] describe Thermodiscus maritimus as an obligate autotroph, but Stetter et al. (1990) [374] list it as a heterotroph.

Furthermore, the majority of known thermophiles and hyperthermophiles are obligately heterotrophic, preferentially using complex mixtures of polypeptides and/or carbohydrates as energy and carbon sources in laboratory growth experiments. Others are strict autotrophs that assimilate CO2, and yet others are able to grow hetero- or autotrophically depending on the availability of carbon sources. It should be noted that the actual carbon compounds metabolized by thermophilic or hyperthermophilic heterotrophs in natural ecosystems are generally not resolved [46].

In addition, all hyperthermophiles and many species of thermophiles are chemosynthetic rather than photosynthetic, deriving energy by the oxidation or reduction of dissolved organic and inorganic compounds rather than by harnessing solar energy. This fact also correlates directly with the geochemistry and geophysics of high temperature ecosystems. These environments are almost exclusively at depths greater than those penetrable by sunlight.

Finally, the majority of thermophiles and hyperthermophiles in culture take advantage of electron transfer among species in the sulfur redox system. Anaerobes commonly reduce sulfate, sulfite, thiosulfate, or elemental sulfur to sulfide, while aerobes may oxidize sulfide or elemental sulfur to sulfate. Of these, perhaps the most common energy-yielding process used by hyperthermophiles is the reduction of elemental sulfur represented by:  

1
formula
This experimentally-verified reaction [47] is believed to be the sole energy-yielding process in numerous autotrophs, although it has been shown [48] that the energy release in hot spring systems is rather moderate relative to other known autotrophic and heterotrophic metabolic reactions.

Comparisons with mesophiles

Thermophiles, and in particular hyperthermophiles, are relatively recent discoveries in microbiology. If the volume of Earth where life may exist is indeed as vast as recently estimated [27], most of the habitable subsurface can only be inhabited by thermophiles and hyperthermophiles. Although considerable progress has already been made in identifying their required substrates for growth in the laboratory, significant gaps still exist in (1) understanding the actual carbon sources of thermophilic heterotrophs in natural biotopes, (2) evaluating the impact of solid phases on metabolism, both as substrates and products, (3) elucidating the pathways of intracellular anabolism and catabolism, and (4) quantifying the energetics of metabolic reactions at the temperature, pressure, and chemical composition of natural systems. In all four cases, the plethora of information and data gathered from studies of mesophilic organisms may provide some useful constraints.

It is the objective of this study to calculate the energetics as functions of temperature and pressure of ‘overall’ metabolic reactions known to be mediated by thermophiles and hyperthermophiles. We have included reactions that are unfamiliar to thermophily if they are experimentally verified energy-yielding processes in mesophiles. In addition, we supply thermodynamic properties of 307 individual aqueous solutes, gases, liquids, and minerals, which permit calculations for thousands of additional reactions that may be of interest as research progresses. Calculations of this sort may aid in identifying likely thermophilic and hyperthermophilic metabolisms not yet observed, as well as in the selection of potential habitats for discovering novel isolates. In a step toward reaching these goals, we present a thermodynamic approach to evaluate quantitatively the energetics of overall metabolic reactions in microorganisms as functions of temperature and pressure.

Thermodynamic framework

Energetics of metabolic reactions at 25°C and 1 bar

Prior to the discovery of thermophiles, energetic calculations at 25°C and 1 bar for metabolic reactions were sufficient for most applications in microbiology. It can be seen in tables and figures presented here that the energetics of the chemical reactions of interest show very little change over a narrow temperature range near 25°C. In other words, applying a thermodynamic value for a specific reaction at 25°C to the same reaction at 15 or 37°C introduces only minimal error. Thauer et al. (1977) [6] published a compilation of thermodynamic calculations at 25°C for energy conservation in chemotrophic anaerobes that is still useful today. However, accurately determining the energetics of metabolic reactions carried out, for example, by P. fumarii at 113°C and 250 bar requires accurate thermodynamic properties at this temperature and pressure. Recent developments of theoretical equations of state permit the calculation of standard partial molal thermodynamic properties of aqueous, liquid, solid, and gaseous organic and inorganic compounds over wide ranges of temperature and pressure. In the present study, we evaluated standard state thermodynamic properties at temperatures up to 200°C, which is well within the range of temperature covered by experimental data and equations of state, and should be sufficient for metabolic energy calculations for even the most optimistic microbiologists.

Internally consistent thermodynamic data at elevated temperatures and pressures

There is always uncertainty in thermodynamic calculations, but some sources can be minimized or even eliminated. Systematic and experimental uncertainties can not be overcome through data interpretation. Mixing of thermodynamic data from various sources can introduce inconsistencies that can cripple the accuracy of calculations. On the other hand, inconsistencies among various sets of thermodynamic data can be resolved by careful analysis. The result is usually called an internally consistent database, which means that thermodynamic properties of a network of reactions have been used to extract corresponding properties of individual compounds. The data and equations used in this study represent one of the most comprehensive internally consistent data sets available for biochemical and geochemical calculations.

The revised Helgeson–Kirkham–Flowers (HKF) equations of state have been combined with experimental calorimetric, densimetric, and sound velocity measurements as well as solubility and dissociation data available in the literature to generate parameters required to calculate standard molal thermodynamic properties at elevated temperatures and pressures for hundreds of aqueous compounds. The classes of compounds for which internally consistent thermodynamic data are now available include aqueous inorganic ions and neutral solutes [49–56], aqueous organic compounds including hydrocarbons, carboxylic acids, ketones, alcohols, aldehydes, amines, amides, chlorinated compounds, amino acids, and peptides [57–67], and metal–organic complexes [68–70]. Discussions of the theoretical foundation for the HKF equations in their original form are given by Helgeson et al. (1981) [71], and in their revised forms by Tanger and Helgeson [72], Shock and Helgeson [49, 57], Shock et al. (1989, 1992) [50, 51], Johnson et al. (1992) [73], and Sverjensky et al. (1997) [55], and relevant equations are presented in the Appendix. In addition, internally consistent data for solid, liquid, and gaseous organic compounds [74, 75] and numerous inorganic gases and rock-forming minerals [56, 76] can be included in these calculations. To underscore the variability of thermodynamic data as functions of temperature and pressure, it seems appropriate to show a few examples of the effects of temperature and pressure on the thermodynamic behavior of gases and aqueous species involved in microbial metabolic reactions.

Gas solubilities

Molecular hydrogen (H2) is a common electron donor (reductant) in thermophilic and hyperthermophilic metabolism. Therefore, the equilibrium constant for H2 dissolution in water as a function of temperature, shown in Fig. 1, is of direct significance. It can be seen in this figure that the logarithm of the equilibrium constant (K) for the H2(g) dissolution reaction minimizes with increasing temperature at constant pressure, (PSAT). The key point to note is that the solubility of H2(g) is moderately temperature dependent. In fact, at PSAT, H2(g) is more than twice as soluble at 200°C than at 50°C.

Figure 1

Log K plotted against temperature at PSAT for the solubility of gaseous H2S (reaction G8), CO2 (reaction G9), CH4 (reaction G10), and H2 (reaction G1).

Figure 1

Log K plotted against temperature at PSAT for the solubility of gaseous H2S (reaction G8), CO2 (reaction G9), CH4 (reaction G10), and H2 (reaction G1).

The solubility of CO2 plays an important role in the metabolism of autotrophs that use it as a carbon source, as well as heterotrophs that produce it as a metabolite. Values of log K for the CO2(g) solubility reaction are also shown in Fig. 1. In contrast to H2, log K for CO2 minimizes at a temperature well above 100°C. In fact, the solubility at PSAT of CO2(g) is nearly eight times higher near 0°C than at 200°C.

CH4 serves as a carbon source for methanotrophs, but it is metabolically produced by methanogens. Its solubility at PSAT is quite temperature dependent at low temperature, but only moderately so above ∼50°C. It can be seen in Fig. 1 that the values of log K for the CH4 solubility reaction minimize at ∼100°C and PSAT, and that CH4(g) is approximately twice as soluble at 2 and 200°C than at 100°C.

Many hyperthermophilic heterotrophs currently in culture depend on the reduction of sulfur to H2S for optimum growth [8]. Therefore, the solubility of H2S as a function of temperature may be useful for understanding their metabolisms. Not unlike that of CO2 discussed above, the solubility of H2S decreases significantly with increasing temperature. This can be interpreted from the values of log K for the H2S solubility reaction shown in Fig. 1. In fact, like CO2, the solubility of H2S(g) at PSAT is approximately eight times higher near 0°C than at 200°C.

Neutrality

The temperature and pH dependencies of dissociation reactions affect many microbial metabolic processes. Many bioenergetic calculations are carried out at pH=7 (see below), because this denotes neutrality at 25°C and 1 bar. However, because neutrality is defined as the pH where activities of H+ and OH are equal, and the dissociation constant for H2O is temperature dependent, the pH representing neutrality also varies with temperature. It can be seen in Fig. 2 that neutral pH, depicted by the curve, decreases at PSAT from ∼7.4 at 0°C to ∼5.6 at 200°C. A pH of 7 carries no special significance at temperatures and pressures other than 25°C and 1 bar. The consequences of this fact can not be ignored when describing metabolic reactions written in terms of species such as CO2, H2S, SO42−, NH3, and organic acids.

Figure 2

Neutral pH depicted by the curve as a function of temperature at PSAT.

Figure 2

Neutral pH depicted by the curve as a function of temperature at PSAT.

At neutral pH, as shown by the dashed curve in Fig. 3a, dissolved CO2 is the dominant species in the carbonic acid system only above ∼80°C; below this temperature, HCO3 dominates at neutrality. It can be inferred from this figure that the equilibrium concentration of CO32− is only significant in highly alkaline solutions, regardless of the temperature. Note in Fig. 3b that at neutral pH the activity of H2S exceeds that of HS to an increasing degree with increasing temperature. In the sulfuric acid system (Fig. 3c), SO42− is the dominant species at alkaline and neutral pHs and well into the acid region over the entire temperature range considered here. However, with increasing temperature in highly acid environments, the activity of HSO4 may rival and even surpass that of SO42−. In the ammonia system (Fig. 3d), NH4+ is the dominant species at neutral pH between 0 and 200°C, although to a lesser degree with increasing temperature.

Figure 3

Temperature–pH diagrams at PSAT for the dissociation of (a) CO2(aq) (reactions H9 and H10); (b) H2S(aq) (reaction H8); (c) HSO4 (reaction H7); (d) NH4+ (reaction H2). The solid curves represent equal activities of the species that predominate on either side of the curves. The dashed lines depict neutral pH (see Fig. 2).

Figure 3

Temperature–pH diagrams at PSAT for the dissociation of (a) CO2(aq) (reactions H9 and H10); (b) H2S(aq) (reaction H8); (c) HSO4 (reaction H7); (d) NH4+ (reaction H2). The solid curves represent equal activities of the species that predominate on either side of the curves. The dashed lines depict neutral pH (see Fig. 2).

pKa values

Changes in temperature have variable effects on pKa values for inorganic and organic acids involved in microbial metabolism, as illustrated with the examples shown in Fig. 4. In some cases, these changes are dramatic, and, as a result, the speciation of metabolites differs considerably between environments at various temperatures even though pH values may be quite similar. For example, at neutral pH, acetate will dominate the speciation of acetic acid solutions at all temperatures from 0 to 200°C as shown in Fig. 4a. On the other hand, acetic acid acting as a buffer can hold the pH between 4.8 and 5.5 over this temperature range. Speciation of succinic acid (Fig. 4b) is dominated by succinate2− at neutral pH and temperatures <∼110°C, and by the monovalent anion, H–succinate, at neutral pH and higher temperatures. Aspartic acid (Fig. 4c) exhibits only the slightest variation in pKa from 0 to 200°C, and that of lysine (Fig. 4d) is not significantly more pronounced. In the three dissociation reactions of phosphoric acid (Fig. 4e), the pH values of the equal activity curves vary only slightly as functions of temperature. H2PO4 dominates at and near-neutral pH, and HPO42− dominates at slightly alkaline pH. H3PO4 and PO43− are only significant in highly acidic (<∼2) or highly alkaline (>∼12) solutions, respectively. The speciation of vanadic acid (Fig. 4f) shows five different protonated and deprotonated forms with H2VO4 being the dominant one at neutral pH over the entire temperature range.

Figure 4

Temperature–pH diagrams at PSAT for the dissociation of (a) acetic acid (reaction H12); (b) succinic acid (reactions H23 and H24); (c) aspartic acid (reaction H28); (d) lysine+ (reaction H31); (e) H3PO4 (reactions H45-H47); (f) VO2+ (reactions H32–H35). The solid curves represent equal activities of the species that predominate on either side of the curves. The dashed lines depict neutral pH (see Fig. 2).

Figure 4

Temperature–pH diagrams at PSAT for the dissociation of (a) acetic acid (reaction H12); (b) succinic acid (reactions H23 and H24); (c) aspartic acid (reaction H28); (d) lysine+ (reaction H31); (e) H3PO4 (reactions H45-H47); (f) VO2+ (reactions H32–H35). The solid curves represent equal activities of the species that predominate on either side of the curves. The dashed lines depict neutral pH (see Fig. 2).

The variations in speciation shown in Fig. 4 help to explain why various solutes behave differently in natural high temperature environments. As an example, in one outflow channel of Octopus Spring at Yellowstone National Park, populated by T. ruber, the pH is 7.88 at 88°C [78]. In contrast, we measured pH as low as 2.12 at only slightly lower temperature in thermal waters from Pozzo Vasca at Vulcano in the Aeolian Islands, southern Italy. At Octopus Spring, the predominant forms of the compounds shown in Fig. 4 would be acetate, succinate2−, aspartate, lysine, H2PO42−, and HVO42−, while at Vulcano, the speciation would be dominated by acetic acid, succinic acid, aspartic acid, lysine+, H3PO4, and VO2+.

Pressure effects

Many thermophiles and hyperthermophiles are also barophiles and may employ metabolic processes that are affected by pressure. In general, the effect of pressure on values of the standard molal Gibbs free energy of formation (ΔG°) between PSAT and 1 kbar is significantly less than the effect of temperature from 0 to 100°C. To illustrate this point, values of ΔG° of aqueous glycine are plotted in Fig. 5 as a function of temperature at various pressures from PSAT to 5 kbar (depicted as contours). It can be seen in this figure that at constant temperature and pressures between PSAT and 1 kbar, values of ΔG° differ by <5 kJ mol−1. Conversely, at constant pressure and temperatures between 0 and 100°C, ΔG° decreases by ∼17 kJ mol−1. A change of this magnitude in ΔG° for aqueous glycine would require a decrease in pressure from 4 kbar to PSAT at constant temperature. In other words, at most conditions of biological interest, the effect of pressure on ΔG° is secondary to that of temperature. Therefore, most thermodynamic properties tabulated in the present communication are calculated as a function of temperature at PSAT rather than as a function of pressure. Nevertheless, in certain environments, the effect of pressure should not be ignored. Indeed, there is no need to make assumptions about pressure effects on the thermodynamic properties of aqueous species or reactions because they can be calculated explicitly with the revised HKF equations of state by integrating the volume with respect to pressure (see below).

Figure 5

ΔG° of aqueous glycine plotted against temperature at PSAT and constant pressure (labeled in kbar).

Figure 5

ΔG° of aqueous glycine plotted against temperature at PSAT and constant pressure (labeled in kbar).

Some further examples of the effects of pressure are shown in Fig. 6 for reactions that are introduced above. It can be seen in Fig. 6a that increasing pressure to 1000 bar (approximately equal to the pressure at a depth of 10 km in seawater) has a slight effect on the pH of neutrality. At 100°C, neutral pH decreases from just above 6.1 to just below 6.0 as pressure increases from 1 to 1000 bar. At 100°C, values of ΔGr° for the CO2 solubility reaction (Fig. 6b) change by ∼3 kJ mol−1 over this same pressure range; those for H2S (Fig. 6c) and acetic acid (Fig. 6d) dissociation change by ∼1.5 and ∼1.0 kJ mol−1, respectively.

Figure 6

ΔG°r (or pH) plotted against pressure at 0, 100, and 200°C for the dissociation of H2O, H2S, and acetic acid as well as for the solubility of CO2(g).

Figure 6

ΔG°r (or pH) plotted against pressure at 0, 100, and 200°C for the dissociation of H2O, H2S, and acetic acid as well as for the solubility of CO2(g).

This set of examples is included here to emphasize the point that the effects of temperature and, to a lesser degree, pressure on the thermodynamic behavior of compounds involved in metabolic processes are often considerable. Calculating the energetics of metabolic processes such as methanogenesis, sulfur reduction, and acetic acid catabolism, to name only a few, can be accomplished with the standard molal thermodynamic properties of all reactants and products at the temperature and pressure of interest, together with their activities in natural or laboratory systems. Traditionally, bioenergetic calculations are conducted at reference conditions which are misleading at best when attempting to evaluate reaction energetics in high temperature/pressure systems.

Moving out of the conventional bioenergetic reference frame

Many bioenergetic calculations are carried out with thermodynamic data at reference conditions of 1 atmosphere (atm), 25°C, and with the additional constraint that pH=7. Although few organisms actually require these environmental conditions, these data are useful when considering the metabolic energy demands of organisms living in near-surface environments where no pressure extrapolation is required, where the variability of temperature has a minimal effect on standard thermodynamic properties, and where near-neutral pH can often be assumed for intracellular fluids owing to homeostasis. On the other hand, acidophilic, barophilic, and thermophilic microorganisms require low pH or high pressures or high temperatures, and some require combinations of these factors. From a geochemical, ecological, or environmental perspective, the conventional biological reference frame for energetic calculations can inhibit meaningful insights into how these organisms live.

The problems introduced by the conventional bioenergetic reference frame are far from trivial. As shown above, direct application of 25°C data to the elevated temperatures that many microorganisms require can introduce enormous errors. In addition, many bioenergetic calculations also convert the standard partial molal Gibbs free energy of reaction (ΔGr°) into a revised version at pH=7, indicated as ΔGr°′. This is done by removing the hydrogen ion (H+) from the standard state adopted for all other aqueous species in the calculation (corresponding to unit activity in a hypothetical 1 molal solution referenced to infinite dilution) and evaluating the free energy contribution of H+ at an activity of 10−7. This conversion is useful for studying processes inside mammalian cells, as well as comparative studies based on well-controlled laboratory conditions. Arguments in defense of this approach are presented by other investigators [79, 80]. However, the adoption of the revised biologic standard state unnecessarily complicates thermodynamic evaluation of the effects of existing natural or laboratory constraints on the bioenergetics of microorganisms. Furthermore, as illustrated above, the pH which corresponds to neutrality depends on pressure and temperature. Therefore, although neutrality may be a useful constraint for applying thermodynamic data in bioenergetic calculations, pH=7 is not.

Values of neutral pH as a function of temperature are determined from values of the equilibrium constant (K) for the reaction:  

2
formula
which in turn are calculated with the relation:  
3
formula

Values of ΔG2° and neutral pH as a function of temperature are given in Table 3. To facilitate the conversion from ΔGr° to ΔGr°′ and vice versa, the contribution of aH+ to ΔGr° (denoted as Gn) as a function of temperature is explicitly listed in Table 3. This conversion, expressed as:  

4
formula
requires accounting for the stoichiometry of H+ in the reaction (υH+). A sample calculation of the interconversion from the standard state adopted in this study and its biological counterpart is presented in the Appendix.

Table 3

The values of ΔGr°, pHneutral, and Gn for the water dissociation reaction H2O(l)=H++OH

T (°C) 18 25 37 45 55 70 85 100 115 150 200 
ΔGr° 78.25 79.34 79.89 80.90 81.63 82.59 84.13 85.78 87.55 89.42 94.22 102.21 
pHneutral 7.43 7.12 7.00 6.82 6.70 6.58 6.41 6.26 6.13 6.02 5.82 5.64 
Gn −39.13 −39.67 −39.95 −40.45 −40.82 −41.30 −42.07 −42.89 −43.78 −44.71 −47.11 −51.11 
T (°C) 18 25 37 45 55 70 85 100 115 150 200 
ΔGr° 78.25 79.34 79.89 80.90 81.63 82.59 84.13 85.78 87.55 89.42 94.22 102.21 
pHneutral 7.43 7.12 7.00 6.82 6.70 6.58 6.41 6.26 6.13 6.02 5.82 5.64 
Gn −39.13 −39.67 −39.95 −40.45 −40.82 −41.30 −42.07 −42.89 −43.78 −44.71 −47.11 −51.11 

Another problem which plagues bioenergetic calculations does not involve the adoption of standard states, but rather confusion about the difference between standard state properties and the overall thermodynamic properties of reactions. It appears to be fairly common practice to use standard state Gibbs free energies to argue whether a reaction can provide energy without bringing in any other environmental constraints. These arguments contravene thermodynamics. It is impossible to tell from the sign of ΔGr° which way a reaction will proceed, unless all of the chemical species in the chemical process of interest are already in their standard states. This can be the case for pure solids, but is generally not the case for aqueous solutes or gases. The direction in which a reaction involving aqueous solutes or gases will proceed can only be determined from the overall Gibbs free energy after evaluating the activities of all of the chemical species in the reaction. If this was not the case, then there would be no need to make chemical analyses of natural or laboratory aqueous systems. The overall Gibbs free energy of a reaction (ΔGr) can be calculated from the familiar expression:  

5
formula
where ΔGr° is as defined above, R and T represent the gas constant and temperature (K), respectively, and Qr denotes the activity product. Values of Qr required to evaluate ΔGr with Eq. 5 can be determined from the relation:  
6
formula
where ai stands for the activity of the ith species, and υi,r represents the stoichiometric reaction coefficient of the ith species in reaction r, which is negative for reactants and positive for products. In the case of gases, activity is replaced by fugacity of the species, fi.

It is the term on the left hand side of Eq. 5, ΔGr, which determines how a reaction will proceed. Indeed, relying on the sign of the first term on the right hand side of this expression, ΔGr°, can be very misleading as illustrated by the example of anaerobic acetic acid oxidation represented by:  

7
formula
At 100°C and PSAT, ΔG7° is positive, and equal to 35.9 kJ mol−1. In shallow hot spring systems, such as those in the Aeolian Islands of Italy, the activity product, Q7, at the prevailing environmental conditions (aCH3COOH=3×10−6; fCO2=2.8×10−2; fH2=4.8×10−5 [46, 81]) is equal to 1.39×10−15. These values of ΔG7° and Q7 combined in Eq. 5 yield a negative value of ΔG7 equal to −70.2 kJ mol−1. Therefore, at the actual environmental conditions, Reaction 7 is energy-yielding (exergonic); i.e., the value of ΔG7 is negative, even though that of ΔG7° is positive.

The energetics of overall autotrophic and heterotrophic reactions discussed below are grouped by chemical system starting with simple systems such as H–O and H–O–N and proceeding to more complex systems involving organic compounds, metal ions, minerals, and multiple oxidation states of sulfur. In each system, we tabulate values of ΔG° at various temperatures (T) for individual solids, gases, and aqueous species, which are calculated from:  

8
formula
where ΔGf° stands for the standard partial molal Gibbs free energy of formation from the elements at the reference temperature (Tr) and pressure (Pr) of 298.15 K and 1 bar, STrPr° represents the standard partial molal entropy at the reference conditions, and CP° and V° designate the standard partial molal isobaric heat capacity and volume, respectively. Evaluating the integrals in Eq. 8 is accomplished with the revised-HKF equation of state (see Appendix). The advantage of this approach is that values of ΔG° can be summed directly to obtain ΔGr° without having to evaluate thermodynamic properties of the elements as functions of temperature and pressure (besides, they cancel across any balanced chemical reaction).

Coupled and linked redox reactions

Microorganisms have developed the means to take advantage of an enormous variety of redox energy sources. As a result, almost every conceivable combination of reduced and oxidized compounds are linked by organisms in overall metabolic processes. Although the biochemical pathways of electron transfer can be quite complicated, mediated by enzymes, and are in many cases unknown, it is useful to break down overall reactions into their constituent redox steps. This can be illustrated by writing half-cell reactions that explicitly include electrons (e) such as:  

9
formula
which is a suitable thermodynamic representation of nitrate reduction to nitrite. This expression would be particularly useful when considering the process going on at an electrode (a cathode) where nitrate is reduced as electrons enter a solution. Half-cell reactions can be combined into coupled redox reactions by conserving electrons; in this case by combining Reaction 9 with:  
10
formula
to yield:  
11
formula
Reaction 11 represents the coupled process of nitrate reduction to nitrite and H2 oxidation to water, and does not explicitly involve electrons even though electrons are transferred in the actual overall reaction.

This sort of representation is particularly useful because the source of electrons in microbial reactions may or may not be known. For example, in the case of an autotroph that gains energy from the knallgas reaction:  

12
formula
H2 is the source of electrons used to reduce O2 to water. However, in the case of a heterotroph, it may only be known that the organism reduces nitrate to nitrite with electrons provided by the oxidation of uncharacterized organic compounds in organic matter (either occurring naturally or from yeast extract or other commonly used constituents of laboratory media). In this case, it may still be useful to consider the energetics of nitrate reduction using Reaction 11 despite the fact that the source of the H2 is unknown. In fact, H2 may be a proxy for hydrogen obtained from organic compounds or, for that matter, electrons obtained through partial or complete oxidation of organic carbon. If the organic compound involved is known, then the coupled organic oxidation and nitrate reduction reactions can be obtained by combining Reaction 11 with the H2-balanced organic oxidation reaction. As an example, oxidation of carbon in formic acid to CO2:  
13
formula
can be combined with Reaction 11 to yield:  
14
formula
Note that this representation of the linked overall redox process of formic acid oxidation and nitrate reduction does not involve H2(aq) or electrons. Nevertheless, the mechanisms of actual biochemical redox pathways may use H2, e, or both.

In our treatment of coupled and linked redox reactions, we have chosen to tabulate standard Gibbs free energies for reactions that are identified with the metabolism of specific microorganisms. If the actual stoichiometry of the reaction has been demonstrated, or is certain for that organism based on the description in the original literature, those reactions are indicated ‘as written’. ‘Inferred’ is used in cases where there is some ambiguity but a reasonable interpretation of the text leads to the conclusion that the reaction is appropriate. Finally, we also list organisms as using ‘hydrogen from an organic source’ if it is apparent that the source of reductant is chosen to be H2 for convenience. These designations apply to coupled reactions involving H2, such as Reaction 11, rather than fully linked redox reactions.

Energetics of microbial metabolic reactions

Is methanotrophy (the consumption of CH4) or methanogenesis (the production of CH4) a viable mode of metabolism in a particular environment? When attempting to isolate from a solfatara a microorganism that uses elemental sulfur, is one likely to find one that oxidizes sulfur to sulfate or one that reduces it to sulfide? In microbial metabolism, acetate is commonly produced as a metabolite, but also consumed as a carbon source; which of these processes is energy-yielding in a particular biotope or growth experiment? In order to answer questions of this type, the overall Gibbs free energies of the appropriate reactions need to be calculated at the temperature, pressure, and chemical composition that obtain in the system of interest. In this section, we present and discuss the standard and overall Gibbs free energies of compounds and reactions in autotrophic and heterotrophic microbial metabolism. Because some prefer to think of reaction energetics in terms of standard potentials, relations between standard Gibbs free energies and standard potentials for oxidation–reduction reactions are also discussed (see Appendix). The focus in this study is on thermophilic Archaea and Bacteria, and thus the thermodynamic properties are computed as a function of temperature. Although the thermodynamic properties for all compounds and reactions given in this review can also be calculated as functions of pressure, those included here are limited to PSAT, unless mentioned otherwise.

In figures depicting solubility and dissociation reactions, temperature is continuous from 0–200°C. However, in most figures and tables, we report values of ΔG° and ΔGr° at representative temperatures, which were chosen as follows: 2°C, the average temperature of the world’s oceans; 18°C, the average temperature of surface ocean waters; 25°C, the accepted standard reference temperature; 37°C, the average body temperature of humans and a temperature at which many thermodynamic properties are measured; 45, 55, and 70°C, three representative growth temperatures in thermophiles; 85, 100, and 115°C, three representative growth temperatures in hyperthermophiles, the last being near the current upper temperature limit for a pure isolate in the laboratory; 150 and 200°C, two temperatures at which hyperthermophilic life may be thriving, although clear laboratory results have yet to confirm this. Values of ΔG° or ΔGr° at temperatures other than those listed in the present tables can be readily determined to high precision by interpolation. Using finite difference derivatives between the two points on either side of the desired temperature will introduce errors in ΔG° on the order of 250 J mol−1 or less, which is well within the uncertainties of the accepted values (see also Fig. 5). Extrapolation below 2°C or above 200°C should be avoided, however, as it may yield values of ΔG° that differ significantly from those computed with revised HKF equations of state. Thermodynamic calculations at temperatures <2 or >200°C can be carried out with the software package SUPCRT92 [73] or ORGANOBIOGEOTHERM.

This section is further divided into subsections. We start with the energetics of overall metabolic processes in the chemical system H–O and note some of the microbes known to catalyze these specific processes (Section 5.1). Section 5.2 deals with compounds and reactions in the chemical system H–O–N, followed sequentially in further subsections by the systems H–O–S, H–O–N–S, H–O–Cinorganic, H–O–C, H–O–N–C, H–O–S–C, H–O–N–S–Camino acid, and H–O–S–C–metals/minerals. Section 5.8 covers the inorganic aqueous chemistry in the H–O–P system and demonstrates the need for thermodynamic data as a function of temperature for organo-phosphate compounds. Finally, although various microorganisms gain metabolic energy from Cl-redox reactions, we decided not to include a discussion in the main body of the text, because there are currently no known thermophiles that mediate these processes (J.D. Coates, 1999, personal communication). Instead, we provide standard Gibbs free energies for Cl-containing (and other halogen-containing) compounds and redox reactions, and identify mesophilic microorganisms responsible for their catalysis, in the Appendix.

The H–O system

Aquifex pyrophilus, a hyperthermophile isolated from hot marine sediments at the Kolbeinsey Ridge, Iceland [82], and other species among the Aquificales gain metabolic energy by reducing oxygen (or oxidizing hydrogen) and forming water via:  

15
formula
Values of ΔGr° for this reaction can be calculated from those of ΔG° for O2, H2 and H2O listed in Table 4.1 consistent with:  
16
formula
The value of ΔGr° will depend on whether the reaction is written to include gases (H2(g), O2(g)) or aqueous species (H2(aq), O2(aq)), liquid H2O (H2O(l)), or water vapor (H2O(v)). Values of ΔG° for all of these chemical species are given in Table 4.1. Other values of ΔG° from Table 4.1 allow evaluation of ΔGr° with Eq. 16 for the dissociation of H2O (Reaction 2), as well as reactions (A1) and (A2) in Table 4.2, and other reactions that may be of interest in microbial metabolism. Values of ΔGr° for the reactions in Table 4.2, calculated with Eq. 16 and consistent with data in Table 4.1 are listed in Table 4.3. These are followed, in Table 4.4, with an inventory of the microorganisms which are known to use these reactions in their overall metabolic processes. For example, besides A. pyrophilus, at least two dozen other species of microorganisms are known to gain metabolic energy by mediating Reaction 15.

Table 4.1

Values of ΔG° (kJ mol−1) at PSAT as a function of temperature for compounds in the system H–O

Compounds T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
O2(g) 4.69 1.44 −2.47 −4.12 −6.20 −9.33 −12.48 −15.64 −18.83 −26.33 −37.20 
O2(aq) 18.82 17.28 16.54 15.18 14.21 12.95 10.95 8.81 6.56 4.19 −1.74 −11.17 
H2O2(aq) −130.74 −133.01 −134.02 −135.75 −136.93 −138.40 −140.64 −142.91 −145.21 −147.54 −153.10 −161.31 
HO2 −66.61 −67.14 −67.32 −67.57 −67.71 −67.84 −67.96 −68.02 −67.99 −67.91 −67.40 −65.88 
H2O(l) −235.64 −236.70 −237.18 −238.04 −238.63 −239.39 −240.57 −241.81 −243.08 −244.41 −247.66 −252.69 
H2O(g) −223.86 −226.82 −228.13 −230.39 −231.90 −233.81 −236.69 −239.59 −243.12 −246.07 −253.04 −263.16 
OH −157.39 −157.36 −157.30 −157.14 −157.00 −156.80 −156.44 −156.02 −155.54 −154.99 −153.44 −150.48 
H+ 
H2(g) 2.98 0.91 −1.57 −2.63 −3.96 −5.97 −8.00 −10.05 −12.12 −17.00 −24.12 
H2(aq) 18.89 18.11 17.72 16.99 16.46 15.76 14.62 13.39 12.08 10.68 7.11 1.33 
Compounds T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
O2(g) 4.69 1.44 −2.47 −4.12 −6.20 −9.33 −12.48 −15.64 −18.83 −26.33 −37.20 
O2(aq) 18.82 17.28 16.54 15.18 14.21 12.95 10.95 8.81 6.56 4.19 −1.74 −11.17 
H2O2(aq) −130.74 −133.01 −134.02 −135.75 −136.93 −138.40 −140.64 −142.91 −145.21 −147.54 −153.10 −161.31 
HO2 −66.61 −67.14 −67.32 −67.57 −67.71 −67.84 −67.96 −68.02 −67.99 −67.91 −67.40 −65.88 
H2O(l) −235.64 −236.70 −237.18 −238.04 −238.63 −239.39 −240.57 −241.81 −243.08 −244.41 −247.66 −252.69 
H2O(g) −223.86 −226.82 −228.13 −230.39 −231.90 −233.81 −236.69 −239.59 −243.12 −246.07 −253.04 −263.16 
OH −157.39 −157.36 −157.30 −157.14 −157.00 −156.80 −156.44 −156.02 −155.54 −154.99 −153.44 −150.48 
H+ 
H2(g) 2.98 0.91 −1.57 −2.63 −3.96 −5.97 −8.00 −10.05 −12.12 −17.00 −24.12 
H2(aq) 18.89 18.11 17.72 16.99 16.46 15.76 14.62 13.39 12.08 10.68 7.11 1.33 
Table 4.2

Hydrogen and oxygen metabolic reactions

A1 H2(aq)+0.5O2(aq)↔H2O(l) 
A2 H2O2(aq)+H2(aq)↔2H2O(l) 
A1 H2(aq)+0.5O2(aq)↔H2O(l) 
A2 H2O2(aq)+H2(aq)↔2H2O(l) 
Table 4.3

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 4.2

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
A1 −263.94 −263.45 −263.17 −262.62 −262.20 −261.63 −260.67 −259.60 −258.44 −257.18 −253.90 −248.44 
A2 −359.43 −358.50 −358.07 −357.31 −356.80 −356.14 −355.13 −354.10 −353.03 −351.95 −349.34 −345.40 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
A1 −263.94 −263.45 −263.17 −262.62 −262.20 −261.63 −260.67 −259.60 −258.44 −257.18 −253.90 −248.44 
A2 −359.43 −358.50 −358.07 −357.31 −356.80 −356.14 −355.13 −354.10 −353.03 −351.95 −349.34 −345.40 
Table 4.4

Microorganisms that use the hydrogen and oxygen reactions specified in Table 4.2

Reaction  
A1 Acidovorax delafieldii, Acidovorax facilis, Alcaligenes xylosoxidans, Ancylobacter aquaticus, Hydrogenophaga palleronii, Pseudomonas hydrogenovora, Xanthobacter autotrophicus[379], P. fumarii[9],Sulfolobus acidocaldarius, Sulfolobus solfataricus, Sulfolobus shibatae, A. brierleyi, A. infernus, M. sedula[293],Bacillus schlegelii[189],Hydrogenobacter halophilus[225],Hydrogenophilus thermoluteolus [228, 229] Calderobacterium hydrogenophilum[195], M. prunae[296], Hydrogenobacter thermophilus[226], P. aerophilum[345], A. pyrophilus[82], Hydrogenobacter acidophilus[224], Sulfurospirillum arcachonense[380] 
A2 Acetobacter peroxidans[381] 
Reaction  
A1 Acidovorax delafieldii, Acidovorax facilis, Alcaligenes xylosoxidans, Ancylobacter aquaticus, Hydrogenophaga palleronii, Pseudomonas hydrogenovora, Xanthobacter autotrophicus[379], P. fumarii[9],Sulfolobus acidocaldarius, Sulfolobus solfataricus, Sulfolobus shibatae, A. brierleyi, A. infernus, M. sedula[293],Bacillus schlegelii[189],Hydrogenobacter halophilus[225],Hydrogenophilus thermoluteolus [228, 229] Calderobacterium hydrogenophilum[195], M. prunae[296], Hydrogenobacter thermophilus[226], P. aerophilum[345], A. pyrophilus[82], Hydrogenobacter acidophilus[224], Sulfurospirillum arcachonense[380] 
A2 Acetobacter peroxidans[381] 

Combining values of ΔGr° from Table 4.3 with those of Qr, calculated with compositional constraints on the reactants and products from natural systems or laboratory experiments, allows evaluation of ΔGr in accord with Eq. 5, which corresponds to the amount of energy available from the environment for the overall reaction used in metabolism. In the case of A. pyrophilus, concentration data on H2 and O2 allow evaluation of ΔGr for Reaction A1. If these data are from the gas phase, then values of ΔGr° for the reaction involving gases will need to be calculated from data in Table 4.1, or values of ΔGr° for the solubility reactions for H2 and O2 from Tables A.3 and A.4 in the Appendix will need to be included with the values of ΔGr° for Reaction A1 in Table 4.3.

Table A.3

Gas solubility reactions

G1 H2(g)↔H2(aq) 
G2 O2(g)↔O2(aq) 
G3 NO(g)↔NO(aq) 
G4 N2O(g)↔N2O(aq) 
G5 N2(g)↔N2(aq) 
G6 NH3(g)↔NH3(aq) 
G7 SO2(g)↔SO2(aq) 
G8 H2S(g)↔H2S(aq) 
G9 CO2(g)↔CO2(aq) 
G10 CH4(g)↔CH4(aq) 
G11 CO(g)↔CO(aq) 
G1 H2(g)↔H2(aq) 
G2 O2(g)↔O2(aq) 
G3 NO(g)↔NO(aq) 
G4 N2O(g)↔N2O(aq) 
G5 N2(g)↔N2(aq) 
G6 NH3(g)↔NH3(aq) 
G7 SO2(g)↔SO2(aq) 
G8 H2S(g)↔H2S(aq) 
G9 CO2(g)↔CO2(aq) 
G10 CH4(g)↔CH4(aq) 
G11 CO(g)↔CO(aq) 
Table A.4

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for the reactions given in Table A.3

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
G1 15.91 17.20 17.72 18.56 19.09 19.72 20.59 21.40 22.13 22.79 24.11 25.46 
G2 14.12 15.85 16.54 17.65 18.34 19.15 20.27 21.28 22.20 23.02 24.59 26.04 
G3a 13.18 14.83 15.49 16.54 17.20 17.96 18.99 19.92 20.75 21.49 22.93 24.39 
G4a 6.62 8.45 9.18 10.35 11.08 11.93 13.09 14.13 15.05 15.87 17.42 18.90 
G5 15.77 17.50 18.18 19.29 19.97 20.78 21.89 22.90 23.82 24.63 26.19 27.63 
G6 −12.24 −10.85 −10.26 −9.25 −8.59 −7.78 −6.59 −5.43 −4.30 −3.19 −0.72 2.59 
G7 −3.12 −1.59 −0.97 0.03 0.66 1.41 2.46 3.44 4.34 5.18 6.88 8.76 
G8 3.65 5.06 5.64 6.56 7.15 7.85 8.82 9.71 10.54 11.29 12.80 14.42 
G9 5.96 7.69 8.38 9.49 10.18 10.99 12.12 13.14 14.07 14.91 16.57 18.29 
G10 13.76 15.56 16.27 17.39 18.08 18.89 20.00 20.98 21.85 22.61 24.02 25.18 
G11 14.73 16.47 17.16 18.25 18.91 19.69 20.74 21.67 22.48 23.19 24.45 25.34 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
G1 15.91 17.20 17.72 18.56 19.09 19.72 20.59 21.40 22.13 22.79 24.11 25.46 
G2 14.12 15.85 16.54 17.65 18.34 19.15 20.27 21.28 22.20 23.02 24.59 26.04 
G3a 13.18 14.83 15.49 16.54 17.20 17.96 18.99 19.92 20.75 21.49 22.93 24.39 
G4a 6.62 8.45 9.18 10.35 11.08 11.93 13.09 14.13 15.05 15.87 17.42 18.90 
G5 15.77 17.50 18.18 19.29 19.97 20.78 21.89 22.90 23.82 24.63 26.19 27.63 
G6 −12.24 −10.85 −10.26 −9.25 −8.59 −7.78 −6.59 −5.43 −4.30 −3.19 −0.72 2.59 
G7 −3.12 −1.59 −0.97 0.03 0.66 1.41 2.46 3.44 4.34 5.18 6.88 8.76 
G8 3.65 5.06 5.64 6.56 7.15 7.85 8.82 9.71 10.54 11.29 12.80 14.42 
G9 5.96 7.69 8.38 9.49 10.18 10.99 12.12 13.14 14.07 14.91 16.57 18.29 
G10 13.76 15.56 16.27 17.39 18.08 18.89 20.00 20.98 21.85 22.61 24.02 25.18 
G11 14.73 16.47 17.16 18.25 18.91 19.69 20.74 21.67 22.48 23.19 24.45 25.34 

aValues from Plyasunov et al. (2001) [452]

The following example should help to illustrate this point, which may be useful for converting values of ΔGr° listed in these tables to values appropriate for a specific application. Converting ΔGr° from Table 4.3 for Reaction A1:  

A1
formula
to that for:  
17
formula
is accomplished by adding  
formula
for:  
G2
formula
and ΔGr° for:  
G1
formula
from Table A.4 in the Appendix. Therefore, using values of ΔGr° from the tables in this review:  
18
formula
At 100°C, ΔGA1° from Table 4.3 is −258.44 kJ mol−1, those for Reactions G2 and G1 from Table A.4 are 22.13 kJ mol−1 and 22.20 kJ mol−1, respectively, and the corresponding value for Reaction 17 is −225.2 kJ mol−1, which can also be calculated directly with the values in Table 4.1 (thereby illustrating a point about internal consistency of data).

In continental or shallow submarine hot springs where species of Aquifex are found, concentrations of H2(aq) and O2(aq) can be at or below the equilibrium saturation values. Activities consistent with these concentrations in near-surface environments are likely to fall in the ranges used to construct the plots in Fig. 7, which show contours of the overall Gibbs free energy for Reaction A1GA1) at 25, 55, 100, and 150°C. The slopes of these contours are dictated by the stoichiometry of Reaction A1. By comparing these four plots it can be seen that the value of ΔGA1 becomes less negative with increasing temperature if the activities of H2 and O2 are held constant.

Figure 7

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction A1 as a function of log aO2 and log aH2. The activity of H2O(l) is taken to be unity.

Figure 7

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction A1 as a function of log aO2 and log aH2. The activity of H2O(l) is taken to be unity.

As an example, we can calculate the value of ΔGA1 with Eq. 5 for a shallow hot spring in the Baia di Levante on the island of Vulcano, Italy, close to the site of isolation for Aquifex aeolicus[83]. The reported temperature and partial pressure of hydrogen gas (PH2) of this spring are 98°C and 4.8×10−5 bar, respectively [81]. The corresponding activity of H2 (3.80×10−8), required to evaluate QA1, was computed from the equilibrium constant at 98°C and 1 bar of the H2 dissolution Reaction G1; the activity of O2 (1.64×10−4) was assumed to be in equilibrium with O2(g) in the atmosphere. The value of QA1 (2.05×109) determined with Eq. 6 was combined in Eq. 5 with the value of ΔGA1° (−258.60 kJ mol−1) at 98°C and 1 bar to yield ΔGA1 (−192.44 kJ mol−1). This calculation shows that 192.44 kJ per mol of H2(g) consumed is the maximum amount of energy available to A. aeolicus or any other hyperthermophile catalyzing the knallgas reaction in this hot spring on Vulcano.

The H–O–N system

In the absence of sufficient free oxygen, denitrifiers, including the thermophiles A. pyrophilus, Thermothrix thiopara, and Pyrobaculum aerophilum, as well as other groups of facultative anaerobes may switch from aerobic to anaerobic respiration using NO3 as the terminal electron acceptor. Other microbes carrying out NO3 reduction are obligate anaerobes, unable to pursue aerobic respiration. However, NO3 is not the only N-bearing compound involved in microbial metabolism. The biochemical cycling of nitrogen among its various inorganic forms involves +5, +3, +2, +1, 0, and −3 oxidation states more familiar as NO3, NO2, NO, N2O, N2, and NH3. Values of ΔG° at various temperatures between 0 and 200°C for these compounds as gases or dissolved ions and associated forms, as appropriate, are listed in Table 5.1. Eleven reactions known to be involved in microbial metabolism are listed in Table 5.2, and the locations of each of these reactions in the biogeochemical cycle of nitrogen are shown in Fig. 8. It can be seen in this figure that five of the overall reactions (B1, B4, B5, B7, and B8) involve the transfer of only one or two electrons, but the others involve the transfer of as many as three (Reactions B6, B9, and B11), five (Reaction B2), six (Reaction B10), and even eight electrons (Reaction B3). Values of ΔGr° as a function of temperature for these reactions are listed in Table 5.3.

Table 5.1

Values of ΔG° (kJ mol−1) at PSAT as a function of temperature for compounds in the system H–O–N

Compounds T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
NO3 −107.45 −109.87 −110.91 −112.66 −113.81 −115.24 −117.35 −119.44 −121.49 −123.52 −128.14 −134.30 
HNO3(aq) −99.44 −102.23 −103.47 −105.64 −107.10 −108.94 −111.75 −114.61 −117.52 −120.47 −127.53 −138.03 
NO2 −29.28 −31.35 −32.22 −33.67 −34.62 −35.79 −37.49 −39.15 −40.77 −42.35 −45.84 −50.29 
HNO2(aq) −47.53 −49.68 −50.63 −52.26 −53.36 −54.74 −56.84 −58.95 −61.09 −63.26 −68.40 −75.98 
NO(g)a 91.39 88.04 86.57 84.03 82.33 80.20 76.99 73.75 70.50 67.23 59.53 48.38 
NO(aq)b 104.56 102.87 102.06 100.58 99.53 98.15 95.98 93.67 91.25 88.72 82.46 72.77 
N2O(g)a 109.22 105.73 104.20 101.55 99.78 97.55 94.18 90.78 87.36 83.91 75.78 63.94 
N2O(aq)c 115.84 114.18 113.38 111.90 110.86 109.48 107.27 104.91 102.41 99.78 93.20 82.83 
N2(g) 4.38 1.34 −2.31 −3.85 −5.79 −8.72 −11.66 −14.63 −17.61 −24.63 −34.82 
N2(aq) 20.15 18.84 18.18 16.98 16.12 14.99 13.18 11.24 9.19 7.02 1.55 −7.19 
NH3(g) −12.06 −15.11 −16.45 −18.77 −20.33 −22.28 −25.23 −28.20 −31.20 −34.23 −41.36 −51.76 
NH3(aq) −24.30 −25.96 −26.71 −28.02 −28.92 −30.06 −31.82 −33.63 −35.50 −37.42 −42.08 −49.17 
NH4+ −76.96 −78.68 −79.45 −80.81 −81.72 −82.89 −84.68 −86.50 −88.37 −90.28 −94.86 −101.70 
Compounds T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
NO3 −107.45 −109.87 −110.91 −112.66 −113.81 −115.24 −117.35 −119.44 −121.49 −123.52 −128.14 −134.30 
HNO3(aq) −99.44 −102.23 −103.47 −105.64 −107.10 −108.94 −111.75 −114.61 −117.52 −120.47 −127.53 −138.03 
NO2 −29.28 −31.35 −32.22 −33.67 −34.62 −35.79 −37.49 −39.15 −40.77 −42.35 −45.84 −50.29 
HNO2(aq) −47.53 −49.68 −50.63 −52.26 −53.36 −54.74 −56.84 −58.95 −61.09 −63.26 −68.40 −75.98 
NO(g)a 91.39 88.04 86.57 84.03 82.33 80.20 76.99 73.75 70.50 67.23 59.53 48.38 
NO(aq)b 104.56 102.87 102.06 100.58 99.53 98.15 95.98 93.67 91.25 88.72 82.46 72.77 
N2O(g)a 109.22 105.73 104.20 101.55 99.78 97.55 94.18 90.78 87.36 83.91 75.78 63.94 
N2O(aq)c 115.84 114.18 113.38 111.90 110.86 109.48 107.27 104.91 102.41 99.78 93.20 82.83 
N2(g) 4.38 1.34 −2.31 −3.85 −5.79 −8.72 −11.66 −14.63 −17.61 −24.63 −34.82 
N2(aq) 20.15 18.84 18.18 16.98 16.12 14.99 13.18 11.24 9.19 7.02 1.55 −7.19 
NH3(g) −12.06 −15.11 −16.45 −18.77 −20.33 −22.28 −25.23 −28.20 −31.20 −34.23 −41.36 −51.76 
NH3(aq) −24.30 −25.96 −26.71 −28.02 −28.92 −30.06 −31.82 −33.63 −35.50 −37.42 −42.08 −49.17 
NH4+ −76.96 −78.68 −79.45 −80.81 −81.72 −82.89 −84.68 −86.50 −88.37 −90.28 −94.86 −101.70 

aSee Table A.2 in the Appendix for thermodynamic properties.

bObtained using the ΔGr° values for NO(g)↔NO(aq) from Plyasunov et al. (2000) [382] together with the value of ΔG° for NO(g) tabulated here.

cObtained using the ΔGr° values for N2O(g)↔N2O(aq) from Plyasunov et al. (2000) [382] together with the value of ΔG° for N2O(g) tabulated here.

Table 5.2

Inorganic nitrogen metabolic reactions

B1 NO3+H2(aq)↔NO2+H2O(l) 
B2 NO3+2.5H2(aq)+H+↔0.5N2(aq)+3H2O(l) 
B3 NO3+4H2(aq)+H+↔NH3(aq)+3H2O(l) 
B4 NO2+0.5O2(aq)↔NO3 
B5 NO2+0.5H2(aq)+H+↔NO(aq)+H2O(l) 
B6 NO2+1.5H2(aq)+H+↔0.5N2(aq)+2H2O(l) 
B7 NO(aq)+0.5H2(aq)↔0.5N2O(aq)+0.5H2O(l) 
B8 0.5N2O(aq)+0.5H2(aq)↔0.5N2(aq)+0.5H2O(l) 
B9 0.5N2(aq)+1.5H2(aq)↔NH3(aq) 
B10a NH3(aq)+1.5O2(aq)↔H++NO2+H2O(l) 
B11 NH3(aq)+NO2+H+↔N2(aq)+2H2O(l) 
B1 NO3+H2(aq)↔NO2+H2O(l) 
B2 NO3+2.5H2(aq)+H+↔0.5N2(aq)+3H2O(l) 
B3 NO3+4H2(aq)+H+↔NH3(aq)+3H2O(l) 
B4 NO2+0.5O2(aq)↔NO3 
B5 NO2+0.5H2(aq)+H+↔NO(aq)+H2O(l) 
B6 NO2+1.5H2(aq)+H+↔0.5N2(aq)+2H2O(l) 
B7 NO(aq)+0.5H2(aq)↔0.5N2O(aq)+0.5H2O(l) 
B8 0.5N2O(aq)+0.5H2(aq)↔0.5N2(aq)+0.5H2O(l) 
B9 0.5N2(aq)+1.5H2(aq)↔NH3(aq) 
B10a NH3(aq)+1.5O2(aq)↔H++NO2+H2O(l) 
B11 NH3(aq)+NO2+H+↔N2(aq)+2H2O(l) 

aDrozd (1976) [383] and Suzuki et al. (1974) [384] note that NH3, rather than NH4+, may be the substrate transferred across the cellular membranes.

Figure 8

Schematic of the microbial nitrogen redox cycle. The numbers in parentheses next to the species represent the oxidation state of N; the labels next to the reaction arrows denote the reaction listed in Table 5.2 and the number of electrons transferred in the process.

Figure 8

Schematic of the microbial nitrogen redox cycle. The numbers in parentheses next to the species represent the oxidation state of N; the labels next to the reaction arrows denote the reaction listed in Table 5.2 and the number of electrons transferred in the process.

Table 5.3

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 5.2

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
B1 −176.36 −176.29 −176.21 −176.05 −175.90 −175.70 −175.34 −174.92 −174.44 −173.91 −172.49 −170.01 
B2 −636.62 −636.09 −635.85 −635.45 −635.18 −634.84 −634.34 −633.84 −633.35 −632.88 −631.86 −630.69 
B3 −699.32 −698.63 −698.23 −697.44 −696.85 −696.03 −694.68 −693.18 −691.56 −689.82 −685.39 −678.26 
B4 −87.58 −87.17 −86.96 −86.57 −86.30 −85.92 −85.33 −84.68 −84.00 −83.27 −81.42 −78.43 
B5 −111.24 −111.53 −111.76 −112.28 −112.71 −113.33 −114.41 −115.68 −117.10 −118.68 −122.92 −130.30 
B6 −460.25 −459.80 −459.64 −459.40 −459.27 −459.14 −459.00 −458.92 −458.91 −458.97 −459.37 −460.68 
B7 −173.90 −173.19 −172.82 −172.15 −171.65 −170.98 −169.95 −168.82 −167.63 −166.37 −163.25 −158.36 
B8 −175.11 −175.08 −175.05 −174.98 −174.92 −174.82 −174.65 −174.44 −174.19 −173.92 −173.21 −172.02 
B9 −62.70 −62.55 −62.38 −61.99 −61.67 −61.19 −60.34 −59.34 −58.21 −56.94 −53.53 −47.57 
B10 −268.85 −268.01 −267.50 −266.46 −265.66 −264.55 −262.66 −260.54 −258.19 −255.63 −248.81 −237.06 
B11 −397.55 −397.25 −397.25 −397.40 −397.60 −397.95 −398.66 −399.58 −400.71 −402.03 −405.85 −413.11 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
B1 −176.36 −176.29 −176.21 −176.05 −175.90 −175.70 −175.34 −174.92 −174.44 −173.91 −172.49 −170.01 
B2 −636.62 −636.09 −635.85 −635.45 −635.18 −634.84 −634.34 −633.84 −633.35 −632.88 −631.86 −630.69 
B3 −699.32 −698.63 −698.23 −697.44 −696.85 −696.03 −694.68 −693.18 −691.56 −689.82 −685.39 −678.26 
B4 −87.58 −87.17 −86.96 −86.57 −86.30 −85.92 −85.33 −84.68 −84.00 −83.27 −81.42 −78.43 
B5 −111.24 −111.53 −111.76 −112.28 −112.71 −113.33 −114.41 −115.68 −117.10 −118.68 −122.92 −130.30 
B6 −460.25 −459.80 −459.64 −459.40 −459.27 −459.14 −459.00 −458.92 −458.91 −458.97 −459.37 −460.68 
B7 −173.90 −173.19 −172.82 −172.15 −171.65 −170.98 −169.95 −168.82 −167.63 −166.37 −163.25 −158.36 
B8 −175.11 −175.08 −175.05 −174.98 −174.92 −174.82 −174.65 −174.44 −174.19 −173.92 −173.21 −172.02 
B9 −62.70 −62.55 −62.38 −61.99 −61.67 −61.19 −60.34 −59.34 −58.21 −56.94 −53.53 −47.57 
B10 −268.85 −268.01 −267.50 −266.46 −265.66 −264.55 −262.66 −260.54 −258.19 −255.63 −248.81 −237.06 
B11 −397.55 −397.25 −397.25 −397.40 −397.60 −397.95 −398.66 −399.58 −400.71 −402.03 −405.85 −413.11 

Among the thermophilic microbes, A. pyrophilus, which can gain metabolic energy from the knallgas reaction as discussed above, also mediates the reduction of NO3 and NO2 represented by Reactions (B1), (B2), and (B6) [82]. Similarly, the anaerobic hyperthermophile Ferroglobus placidus, isolated from a shallow submarine hydrothermal system on the island of Vulcano, Italy, catalyzes the conversion of NO3 to NO2 (Reaction B1) and NO2 to NO (Reaction B5) [84]. Several other microbes responsible for mediating the reactions given in Table 5.2 are listed in Table 5.4.

Table 5.4

Microorganisms that use the nitrogen reactions specified in Table 5.2

Reaction  
B1 As written: F. placidus[84], A. pyrophilus[82], Veillonella alcalescens, Micrococcus denitrificans, Thiobacillus denitrificans[6] 
 Inferred: B. schlegelii[189],C. hydrogenophilum[195] 
 Hydrogen from an organic source:Pseudomonas strain MT-1 [385], Silicibacter lacuscaerulensis[386], P. aerophilum[345], Thermothrix thioparus [277, 278], Clostridium perfringens, Aerobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa, Pseudomonas denitrificans, Spirillum itersoni, Selenomonas ruminantium[6] 
B2 As written:A. pyrophilus[82], M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:P. aerophilum[345], T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B3 As written:Ammonifex degensii[187], P. fumarii ([9], V. alcalescens[6] 
B4 As written:Nitrobacter, Nitrospina, Nitrococcus[387] 
B5 As written:F. placidus[84], M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B6 As written:A. pyrophilus[82], M. denitrificans, T. denitrificans[6]
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B7 As written:M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B8 As written:M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B9 As written:Methanosarcina barkeri[388], Desulfovibrio gigas, Desulfovibrio vulgaris, Desulfovibrio desulfuricans, Desulfovibrio salexigens[389], Desulfovibrio africanus [389, 390], Desulfovibrio baculatus[390] 
B10 As written:Nitrosococcus, Nitrosomonas, Nitrosospira, Nitrosovibrio[387], Nitrosolobus[391] 
B11 As written:Planctomycete [85, 86, 392
Reaction  
B1 As written: F. placidus[84], A. pyrophilus[82], Veillonella alcalescens, Micrococcus denitrificans, Thiobacillus denitrificans[6] 
 Inferred: B. schlegelii[189],C. hydrogenophilum[195] 
 Hydrogen from an organic source:Pseudomonas strain MT-1 [385], Silicibacter lacuscaerulensis[386], P. aerophilum[345], Thermothrix thioparus [277, 278], Clostridium perfringens, Aerobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa, Pseudomonas denitrificans, Spirillum itersoni, Selenomonas ruminantium[6] 
B2 As written:A. pyrophilus[82], M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:P. aerophilum[345], T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B3 As written:Ammonifex degensii[187], P. fumarii ([9], V. alcalescens[6] 
B4 As written:Nitrobacter, Nitrospina, Nitrococcus[387] 
B5 As written:F. placidus[84], M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B6 As written:A. pyrophilus[82], M. denitrificans, T. denitrificans[6]
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B7 As written:M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B8 As written:M. denitrificans, T. denitrificans[6] 
 Hydrogen from an organic source:T. thioparus [277, 278], C. perfringens, P. aeruginosa, P. denitrificans[6] 
B9 As written:Methanosarcina barkeri[388], Desulfovibrio gigas, Desulfovibrio vulgaris, Desulfovibrio desulfuricans, Desulfovibrio salexigens[389], Desulfovibrio africanus [389, 390], Desulfovibrio baculatus[390] 
B10 As written:Nitrosococcus, Nitrosomonas, Nitrosospira, Nitrosovibrio[387], Nitrosolobus[391] 
B11 As written:Planctomycete [85, 86, 392

Analogous to the approach described for the H–O system above, values of ΔGr in the H–O–N system can be evaluated by combining values of ΔGr° from Table 5.3 with those of Qr calculated with compositional data on the reactants and products in the geochemical or laboratory environment of interest. Activities of NO3, NO2, and H2 likely to be encountered in hot springs where A. pyrophilus and F. placidus can be found are in the ranges depicted in Figs. 9–11. In order to accommodate the three compositional variables (H2, NO3, and NO2) in two-dimensional plots, three sets of figures at four temperatures (25, 55, 100, and 150°C) were constructed, each set evaluated at a different value of H2 activity (10−3 in Fig. 9, 10−5 in Fig. 10, and 10−7 in Fig. 11). In these figures, values of ΔGB1 at the four temperatures are shown as contours. As in the example for the knallgas reaction discussed above, the slopes of the contour lines in Figs. 9–11 are set by the stoichiometry of reaction (B1). It can be seen in these figures that ΔGB1 increases with increasing temperature at constant activities of NO3, NO2, and H2.

Figure 9

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction (B1) as a function of log aNO2− and log aNO3−. The activity of H2(aq) is set at 10−3, and the activity of H2O(l) is taken to be unity.

Figure 9

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction (B1) as a function of log aNO2− and log aNO3−. The activity of H2(aq) is set at 10−3, and the activity of H2O(l) is taken to be unity.

Figure 10

Same as for Fig. 9, except that the activity of H2(aq) is set at 10−5.

Figure 10

Same as for Fig. 9, except that the activity of H2(aq) is set at 10−5.

Figure 11

Same as for Fig. 9, except that the activity of H2(aq) is set at 10−7.

Figure 11

Same as for Fig. 9, except that the activity of H2(aq) is set at 10−7.

The reactions listed in Table 5.2 are limited to those that can be linked to specific microorganisms. Thus, this table is limited by our ignorance about novel metabolic pathways rather than by reactions that are thermodynamically and geochemically plausible as energy sources for thermophiles and hyperthermophiles. As an example, many hot springs have concentrations of ammonium and nitrate that are out of equilibrium with respect to the reaction:  

19
formula
It follows that it is plausible that an organism may exist that can obtain metabolic energy by combining ammonium and nitrate to form nitrogen. If so, this metabolism would also tend to acidify the environment, or be affected by changes in pH brought about by other coexisting organisms. In fact, Reaction 19 was proposed more than two decades ago as a metabolic process in chemosynthetic microbes [85], but it has never been observed. Recently, Strous et al. (1999) [86], described the cultivation of an organism able to metabolize a process very similar to Reaction 19, namely the anaerobic oxidation of ammonia to nitrogen using nitrite as the electron acceptor (reaction B11). This reaction too had been expected but went undetected for decades.

The H–O–S system

The ghastly stench of hydrogen sulfide is instantly familiar to anyone who has ever stepped foot on the island of Vulcano, north of Sicily or visited the Phlegrean solfatara near Naples, Italy. It is also unforgettable to anyone who has ever cultured a sulfur reducer such as Pyrodictium, Acidianus, Thermococcus, Pyrococcus, or Desulfurococcus, to name only a few. H2S, in which sulfur is in the −2 oxidation state (Sox), is only one of several familiar forms of inorganic sulfur. The others include SO42−, SO32−, and S, in which Sox equals +6, +4, and 0, respectively. In addition, less common sulfur compounds exhibit a wide variety of other oxidation states. Of note in this regard are sulfur compounds with two or more S atoms, some of which have fractional nominal oxidation states. These compounds include the following, in decreasing order of Sox, as well as their associated protonated forms: S2O82− (Sox=+7), S2O62− (Sox=+5), S2O52− (Sox=+4), S3O62− (Sox=+3⅓), S2O42− (Sox=+3), S4O62− (Sox=+23½), S2O32− (Sox=+2), S5O62− (Sox=+2), S52− (Sox=−3⅖), S42− (Sox=−3½), S32− (Sox=−3⅔), S22− (Sox=−1). This wealth of oxidation state possibilities is represented by the 27 sulfur compounds for which values of ΔG° are listed in Table 6.1, and leads to a complex inorganic sulfur cycle much of which is mediated by microbes. As an example, 22 reactions known to be conducted by microbes are listed in Table 6.2, and corresponding values of ΔGr° are given in Table 6.3. It should be recognized that hundreds of other sulfur redox reactions are possible.

Table 6.1

Values of ΔG° (kJ mol−1) at PSAT as a function of temperature for compounds in the system H–O–S

Compound T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
SO42− −743.74 −744.30 −744.46 −744.63 −744.68 −744.68 −744.56 −744.32 −743.94 −743.44 −741.72 −737.75 
HSO4 −752.89 −754.88 −755.76 −757.27 −758.29 −759.56 −761.49 −763.43 −765.38 −767.33 −771.89 −778.22 
SO32− −486.98 −486.78 −486.60 −486.18 −485.84 −485.35 −484.48 −483.47 −482.30 −481.00 −477.35 −470.48 
HSO3 −524.50 −526.75 −527.73 −529.41 −530.52 −531.92 −534.02 −536.12 −538.21 −540.31 −545.13 −551.79 
SO2(aq) −297.64 −300.05 −301.17 −303.16 −304.53 −306.29 −309.03 −311.88 −314.83 −317.88 −325.32 −336.72 
SO2(g) −294.52 −298.46 −300.19 −303.18 −305.19 −307.70 −311.49 −315.32 −319.17 −323.05 −332.19 −345.49 
S2O32− −520.79 −522.10 −522.59 −523.33 −523.78 −524.28 −524.92 −525.44 −525.83 −526.10 −526.21 −524.89 
HS2O3 −529.28 −531.31 −532.21 −533.74 −534.77 −536.06 −538.01 −539.97 −541.93 −543.89 −548.46 −554.80 
H2S2O3(aq) −531.33 −534.25 −535.56 −537.84 −539.39 −541.37 −544.38 −547.47 −550.61 −553.83 −561.55 −573.14 
S2O42− −598.07 −599.74 −600.41 −601.46 −602.12 −602.89 −603.96 −604.91 −605.76 −606.49 −607.74 −608.17 
HS2O4 −611.17 −613.57 −614.63 −616.48 −617.73 −619.29 −621.68 −624.10 −626.54 −629.01 −634.80 −643.04 
H2S2O4(aq) −611.97 −615.24 −616.73 −619.32 −621.09 −623.34 −626.80 −630.34 −633.97 −637.68 −646.64 −660.13 
S2O52− −788.16 −790.03 −790.78 −791.99 −792.75 −793.65 −794.91 −796.07 −797.13 −798.07 −799.83 −801.01 
S2O62− −963.42 −965.61 −966.51 −967.97 −968.91 −970.03 −971.62 −973.12 −974.52 −975.82 −978.41 −980.85 
S2O82− −1109.30 −1113.30 −1115.00 −1118.00 −1119.90 −1122.20 −1125.80 −1129.20 −1132.60 −1135.90 −1143.40 −1153.20 
S3O62− −954.77 −957.16 −958.14 −959.76 −960.79 −962.04 −963.84 −965.54 −967.15 −968.66 −971.76 −974.96 
S4O62− −1034.50 −1038.80 −1040.60 −1043.60 −1045.70 −1048.10 −1051.80 −1055.50 −1059.10 −1062.60 −1070.50 −1080.90 
S5O62− −954.12 −956.96 −958.14 −960.11 −961.39 −962.95 −965.21 −967.39 −969.48 −971.48 −975.77 −980.73 
S(s) 0.71 0.22 −0.39 −0.65 −0.99 −1.51 −2.04 −2.59 −3.17 −4.70 −7.08 
HS 13.63 12.45 11.97 11.17 10.66 10.04 9.16 8.33 7.55 6.82 5.33 3.85 
H2S(aq) −25.21 −27.06 −27.92 −29.47 −30.55 −31.94 −34.12 −36.39 −38.76 −41.23 −47.30 −56.69 
H2S(g) −28.86 −32.12 −33.56 −36.04 −37.70 −39.79 −42.93 −46.10 −49.30 −52.51 −60.10 −71.12 
S2(g) 84.52 80.89 79.30 76.55 74.71 72.40 68.92 65.42 61.90 58.35 50.00 37.90 
S22− 80.43 79.72 79.50 79.22 79.09 79.00 78.99 79.12 79.38 79.78 81.30 85.08 
S32− 75.41 74.12 73.63 72.90 72.46 71.97 71.35 70.85 70.47 70.22 70.16 71.56 
S42− 71.63 69.77 69.03 67.84 67.09 66.21 64.98 63.86 62.85 61.96 60.33 59.37 
S52− 69.11 66.68 65.68 64.04 62.98 61.71 59.87 58.13 56.49 54.94 51.76 48.44 
Compound T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
SO42− −743.74 −744.30 −744.46 −744.63 −744.68 −744.68 −744.56 −744.32 −743.94 −743.44 −741.72 −737.75 
HSO4 −752.89 −754.88 −755.76 −757.27 −758.29 −759.56 −761.49 −763.43 −765.38 −767.33 −771.89 −778.22 
SO32− −486.98 −486.78 −486.60 −486.18 −485.84 −485.35 −484.48 −483.47 −482.30 −481.00 −477.35 −470.48 
HSO3 −524.50 −526.75 −527.73 −529.41 −530.52 −531.92 −534.02 −536.12 −538.21 −540.31 −545.13 −551.79 
SO2(aq) −297.64 −300.05 −301.17 −303.16 −304.53 −306.29 −309.03 −311.88 −314.83 −317.88 −325.32 −336.72 
SO2(g) −294.52 −298.46 −300.19 −303.18 −305.19 −307.70 −311.49 −315.32 −319.17 −323.05 −332.19 −345.49 
S2O32− −520.79 −522.10 −522.59 −523.33 −523.78 −524.28 −524.92 −525.44 −525.83 −526.10 −526.21 −524.89 
HS2O3 −529.28 −531.31 −532.21 −533.74 −534.77 −536.06 −538.01 −539.97 −541.93 −543.89 −548.46 −554.80 
H2S2O3(aq) −531.33 −534.25 −535.56 −537.84 −539.39 −541.37 −544.38 −547.47 −550.61 −553.83 −561.55 −573.14 
S2O42− −598.07 −599.74 −600.41 −601.46 −602.12 −602.89 −603.96 −604.91 −605.76 −606.49 −607.74 −608.17 
HS2O4 −611.17 −613.57 −614.63 −616.48 −617.73 −619.29 −621.68 −624.10 −626.54 −629.01 −634.80 −643.04 
H2S2O4(aq) −611.97 −615.24 −616.73 −619.32 −621.09 −623.34 −626.80 −630.34 −633.97 −637.68 −646.64 −660.13 
S2O52− −788.16 −790.03 −790.78 −791.99 −792.75 −793.65 −794.91 −796.07 −797.13 −798.07 −799.83 −801.01 
S2O62− −963.42 −965.61 −966.51 −967.97 −968.91 −970.03 −971.62 −973.12 −974.52 −975.82 −978.41 −980.85 
S2O82− −1109.30 −1113.30 −1115.00 −1118.00 −1119.90 −1122.20 −1125.80 −1129.20 −1132.60 −1135.90 −1143.40 −1153.20 
S3O62− −954.77 −957.16 −958.14 −959.76 −960.79 −962.04 −963.84 −965.54 −967.15 −968.66 −971.76 −974.96 
S4O62− −1034.50 −1038.80 −1040.60 −1043.60 −1045.70 −1048.10 −1051.80 −1055.50 −1059.10 −1062.60 −1070.50 −1080.90 
S5O62− −954.12 −956.96 −958.14 −960.11 −961.39 −962.95 −965.21 −967.39 −969.48 −971.48 −975.77 −980.73 
S(s) 0.71 0.22 −0.39 −0.65 −0.99 −1.51 −2.04 −2.59 −3.17 −4.70 −7.08 
HS 13.63 12.45 11.97 11.17 10.66 10.04 9.16 8.33 7.55 6.82 5.33 3.85 
H2S(aq) −25.21 −27.06 −27.92 −29.47 −30.55 −31.94 −34.12 −36.39 −38.76 −41.23 −47.30 −56.69 
H2S(g) −28.86 −32.12 −33.56 −36.04 −37.70 −39.79 −42.93 −46.10 −49.30 −52.51 −60.10 −71.12 
S2(g) 84.52 80.89 79.30 76.55 74.71 72.40 68.92 65.42 61.90 58.35 50.00 37.90 
S22− 80.43 79.72 79.50 79.22 79.09 79.00 78.99 79.12 79.38 79.78 81.30 85.08 
S32− 75.41 74.12 73.63 72.90 72.46 71.97 71.35 70.85 70.47 70.22 70.16 71.56 
S42− 71.63 69.77 69.03 67.84 67.09 66.21 64.98 63.86 62.85 61.96 60.33 59.37 
S52− 69.11 66.68 65.68 64.04 62.98 61.71 59.87 58.13 56.49 54.94 51.76 48.44 
Table 6.2

Inorganic sulfur metabolic reactions

C1 SO42−+4H2(aq)+2H+↔H2S(aq)+4H2O(l) 
C2 4SO32−+2H+↔3SO42−+H2S(aq) 
C3 SO32−+3H2(aq)+2H+↔H2S(aq)+3H2O(l) 
C4 SO2(aq)+H2O(l)+S(s)↔H2S2O3(aq) 
C5 S2O32−+2O2(aq)+H2O(l)↔2SO42−+2H+ 
C6 6S2O32−+5O2(aq)↔4SO42−+2S4O62− 
C7 5S2O32−+H2O(l)+4O2(aq)↔6SO42−+2H++4S(s) 
C8 S2O32−+H2O(l)↔SO42−+H2S(aq) 
C9 S2O32−↔SO32−+S(s) 
C10 S2O32−+2H++4H2(aq)↔2H2S(aq)+3H2O(l) 
C11 4S2O42−+4H2O(l)↔3H2S(aq)+5SO42−+2H+ 
C12 S3O62−+2O2(aq)+2H2O(l)↔3SO42−+4H+ 
C13 S3O62−+H2O(l)=SO42−+S2O32−+2H+ 
C14 2S4O62−+6H2O(l)+7O2(aq)↔8SO42−+12H+ 
C15 S4O62−+H2(aq)↔2S2O32−+2H+ 
C16 S(s)+1.5O2(aq)+H2O(l)↔SO42−+2H+ 
C17 4S(s)+4H2O(l)↔SO42−+3H2S(aq)+2H+ 
C18 S(s)+O2(aq)+H2O(l)↔H++HSO3 
C19 S(s)+H2(aq)↔H2S(aq) 
C20 H2S(aq)+2O2(aq)↔SO42−+2H+ 
C21 2H2S(aq)+2O2(aq)↔S2O32−+H2O(l)+2H+ 
C22 H2S(aq)+0.5O2(aq)↔S(s)+H2O(l) 
C1 SO42−+4H2(aq)+2H+↔H2S(aq)+4H2O(l) 
C2 4SO32−+2H+↔3SO42−+H2S(aq) 
C3 SO32−+3H2(aq)+2H+↔H2S(aq)+3H2O(l) 
C4 SO2(aq)+H2O(l)+S(s)↔H2S2O3(aq) 
C5 S2O32−+2O2(aq)+H2O(l)↔2SO42−+2H+ 
C6 6S2O32−+5O2(aq)↔4SO42−+2S4O62− 
C7 5S2O32−+H2O(l)+4O2(aq)↔6SO42−+2H++4S(s) 
C8 S2O32−+H2O(l)↔SO42−+H2S(aq) 
C9 S2O32−↔SO32−+S(s) 
C10 S2O32−+2H++4H2(aq)↔2H2S(aq)+3H2O(l) 
C11 4S2O42−+4H2O(l)↔3H2S(aq)+5SO42−+2H+ 
C12 S3O62−+2O2(aq)+2H2O(l)↔3SO42−+4H+ 
C13 S3O62−+H2O(l)=SO42−+S2O32−+2H+ 
C14 2S4O62−+6H2O(l)+7O2(aq)↔8SO42−+12H+ 
C15 S4O62−+H2(aq)↔2S2O32−+2H+ 
C16 S(s)+1.5O2(aq)+H2O(l)↔SO42−+2H+ 
C17 4S(s)+4H2O(l)↔SO42−+3H2S(aq)+2H+ 
C18 S(s)+O2(aq)+H2O(l)↔H++HSO3 
C19 S(s)+H2(aq)↔H2S(aq) 
C20 H2S(aq)+2O2(aq)↔SO42−+2H+ 
C21 2H2S(aq)+2O2(aq)↔S2O32−+H2O(l)+2H+ 
C22 H2S(aq)+0.5O2(aq)↔S(s)+H2O(l) 
Table 6.3

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 6.2

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
C1 −299.58 −302.00 −303.08 −304.96 −306.24 −307.85 −310.33 −312.86 −315.46 −318.13 −324.67 −335.03 
C2 −308.53 −312.86 −314.91 −318.62 −321.21 −324.58 −329.89 −335.49 −341.39 −347.55 −363.05 −388.02 
C3 −301.82 −304.71 −306.04 −308.38 −309.98 −312.04 −315.22 −318.52 −321.94 −325.48 −334.27 −348.28 
C4 1.23 2.28 2.79 3.74 4.42 5.31 6.73 8.26 9.90 11.63 16.13 23.35 
C5 −768.68 −764.38 −762.23 −758.24 −755.38 −751.59 −745.53 −739.02 −732.09 −724.75 −706.09 −675.58 
C6 −2013.30 −2008.60 −2006.20 −2001.70 −1998.40 −1994.10 −1987.10 −1979.70 −1971.70 −1963.30 −1941.90 −1907.60 
C7 −1695.30 −1686.90 −1682.80 −1675.30 −1670.00 −1663.10 −1652.00 −1640.30 −1628.00 −1615.20 −1583.50 −1533.00 
C8 −12.52 −12.57 −12.61 −12.72 −12.82 −12.95 −13.19 −13.47 −13.80 −14.16 −15.15 −16.87 
C9 34.53 35.53 35.98 36.76 37.28 37.94 38.93 39.93 40.93 41.93 44.15 47.33 
C10 −312.10 −314.57 −315.70 −317.69 −319.06 −320.80 −323.52 −326.33 −329.26 −332.29 −339.82 −351.90 
C11 −459.50 −456.93 −455.71 −453.53 −452.01 −450.07 −447.05 −443.91 −440.65 −437.28 −428.89 −415.39 
C12 −842.80 −836.93 −833.95 −828.40 −824.41 −819.11 −810.60 −801.42 −791.63 −781.22 −754.59 −710.57 
C13 −74.12 −72.54 −71.72 −70.17 −69.03 −67.52 −65.07 −62.41 −59.54 −56.47 −48.51 −34.99 
C14 −2598.70 −2577.70 −2567.20 −2547.80 −2533.80 −2515.50 −2486.00 −2454.40 −2420.80 −2385.30 −2294.60 −2145.90 
C15 −25.94 −23.55 −22.32 −20.03 −18.37 −16.17 −12.62 −8.78 −4.68 −0.30 10.97 29.78 
C16 −537.03 −533.75 −532.09 −528.97 −526.72 −523.73 −518.90 −513.69 −508.10 −502.14 −486.75 −461.23 
C17 120.37 120.44 120.51 120.67 120.82 121.03 121.41 121.89 122.47 123.20 125.84 131.23 
C18 −308.39 −307.55 −307.09 −306.16 −305.46 −304.49 −302.88 −301.08 −299.09 −296.91 −291.03 −280.86 
C19 −44.81 −45.39 −45.64 −46.07 −46.35 −46.71 −47.23 −47.74 −48.25 −48.73 −49.71 −50.95 
C20 −756.16 −751.81 −749.62 −745.51 −742.56 −738.64 −732.34 −725.54 −718.29 −710.59 −690.94 −658.72 
C21 −743.64 −739.24 −737.00 −732.79 −729.74 −725.69 −719.15 −712.07 −704.49 −696.43 −675.79 −641.85 
C22 −219.13 −218.06 −217.53 −216.55 −215.84 −214.92 −213.44 −211.86 −210.19 −208.45 −204.20 −197.48 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
C1 −299.58 −302.00 −303.08 −304.96 −306.24 −307.85 −310.33 −312.86 −315.46 −318.13 −324.67 −335.03 
C2 −308.53 −312.86 −314.91 −318.62 −321.21 −324.58 −329.89 −335.49 −341.39 −347.55 −363.05 −388.02 
C3 −301.82 −304.71 −306.04 −308.38 −309.98 −312.04 −315.22 −318.52 −321.94 −325.48 −334.27 −348.28 
C4 1.23 2.28 2.79 3.74 4.42 5.31 6.73 8.26 9.90 11.63 16.13 23.35 
C5 −768.68 −764.38 −762.23 −758.24 −755.38 −751.59 −745.53 −739.02 −732.09 −724.75 −706.09 −675.58 
C6 −2013.30 −2008.60 −2006.20 −2001.70 −1998.40 −1994.10 −1987.10 −1979.70 −1971.70 −1963.30 −1941.90 −1907.60 
C7 −1695.30 −1686.90 −1682.80 −1675.30 −1670.00 −1663.10 −1652.00 −1640.30 −1628.00 −1615.20 −1583.50 −1533.00 
C8 −12.52 −12.57 −12.61 −12.72 −12.82 −12.95 −13.19 −13.47 −13.80 −14.16 −15.15 −16.87 
C9 34.53 35.53 35.98 36.76 37.28 37.94 38.93 39.93 40.93 41.93 44.15 47.33 
C10 −312.10 −314.57 −315.70 −317.69 −319.06 −320.80 −323.52 −326.33 −329.26 −332.29 −339.82 −351.90 
C11 −459.50 −456.93 −455.71 −453.53 −452.01 −450.07 −447.05 −443.91 −440.65 −437.28 −428.89 −415.39 
C12 −842.80 −836.93 −833.95 −828.40 −824.41 −819.11 −810.60 −801.42 −791.63 −781.22 −754.59 −710.57 
C13 −74.12 −72.54 −71.72 −70.17 −69.03 −67.52 −65.07 −62.41 −59.54 −56.47 −48.51 −34.99 
C14 −2598.70 −2577.70 −2567.20 −2547.80 −2533.80 −2515.50 −2486.00 −2454.40 −2420.80 −2385.30 −2294.60 −2145.90 
C15 −25.94 −23.55 −22.32 −20.03 −18.37 −16.17 −12.62 −8.78 −4.68 −0.30 10.97 29.78 
C16 −537.03 −533.75 −532.09 −528.97 −526.72 −523.73 −518.90 −513.69 −508.10 −502.14 −486.75 −461.23 
C17 120.37 120.44 120.51 120.67 120.82 121.03 121.41 121.89 122.47 123.20 125.84 131.23 
C18 −308.39 −307.55 −307.09 −306.16 −305.46 −304.49 −302.88 −301.08 −299.09 −296.91 −291.03 −280.86 
C19 −44.81 −45.39 −45.64 −46.07 −46.35 −46.71 −47.23 −47.74 −48.25 −48.73 −49.71 −50.95 
C20 −756.16 −751.81 −749.62 −745.51 −742.56 −738.64 −732.34 −725.54 −718.29 −710.59 −690.94 −658.72 
C21 −743.64 −739.24 −737.00 −732.79 −729.74 −725.69 −719.15 −712.07 −704.49 −696.43 −675.79 −641.85 
C22 −219.13 −218.06 −217.53 −216.55 −215.84 −214.92 −213.44 −211.86 −210.19 −208.45 −204.20 −197.48 

In addition to simple redox reactions among pairs of compounds, several of the reactions listed in Table 6.2 involve disproportionation of sulfur among various oxidation states. As an example, thiosulfate, S2O32−, can disproportionate to SO42− and H2S (reaction C8). As long as the products are produced in equal proportions, the overall oxidation state of sulfur does not change during the reaction. However, the nominal oxidation state of each of the sulfur atoms in S2O32− (Sox=+2) changes to +6 (SO42−) or −2 (H2S) as the reaction proceeds. Although Reaction (C8) does not contain H2 or O2, both reduction and oxidation occur as the reaction proceeds. Other sulfur disproportionation reactions listed in Table 6.2 include (C2), (C4), (C6), (C7), (C9), (C11), (C13), and (C17). Many of the microorganisms known to catalyze the reactions listed in Table 6.2 are given in Table 6.4.

Table 6.4

Microorganisms that use the sulfur reactions specified in Table 6.2

Reaction  
C1 As written:Archaeoglobus lithotrophicus[37], Desulfotomaculum auripigmentum[393], Desulfacinum infernum[206], Desulfonatronum lacustre[394], Thermodesulfobacterium mobile[265], Thermodesulfobacterium commune[263], Desulfotomaculum putei[175], Desulfotomaculum luciae [175, 208], Archaeoglobus profundus[331], Thermodesulfovibrio yellowstonii[267], Desulfotomaculum kuznetsovii[207], Desulfotomaculum geothermicum[35], Desulfonatronovibrio hydrogenovorans[395], Desulfotomaculum thermocisternum[180], Desulfotomaculum thermosapovorans[212], A. degensii[187], Desulfotomaculum australicum[170], Desulfotomaculum halophilum[178], Desulfobulbus rhabdoformis[396], D. desulfuricans[381], Desulfotomaculum thermoacetoxidans[210] 
 Hydrogen from an organic source:Archaeoglobus fulgidus [328–330], Thermocladium modestius[259] 
C2 As written:Desulfovibrio sulfodismutans [397, 398], Desulfocapsa sulfoexigens[399], Desulfocapsa thiozymogenes[400] 
C3 As written:D. desulfuricans[381], D. infernum[206], D. lacustre[394], A. veneficus[295], D. putei[175], A. profundus[331], T. yellowstonii[267], D. kuznetsovii[207], D. hydrogenovorans[395], D. thermocisternum[180], D. thermosapovorans[212], D. halophilum[178], D. rhabdoformis[396], Desulfurobacterium thermolithotrophum[216], Pyrodictium brockii[352] 
 Hydrogen from an organic source:A. fulgidus [328–330], Pyrobaculum islandicum[346] 
C4 As written:Thiobacillus thiooxidans, T. thioparus[381] 
C5 As written:Thiobacillus novellus[381], A. pyrophilus[82], P. aerophilum[345], Thermothrix azorensis[276], T. thiopara [277, 278], Thiobacillus hydrothermalis[401], Thiomicrospira crunogena[402], Thiomicrospira chilensis[403] 
C6 As written:Thiobacillus neapolitanus[381] 
C7 As written:T. thioparus[381] 
C8 As written:D. sulfodismutans [397, 398], D. sulfoexigens[399], D. thiozymogenes[400], D. hydrogenovorans[395] 
C9 As written: purple and green photosynthetic Bacteria [404] 
C10 As written:A. fulgidus[329], D. infernum[206], F. placidus[84], D. lacustre[394], P. occultum[352], A. veneficus[295], D. putei[175], D. luciae [175, 208], A. profundus[331], T. yellowstonii[267], D. kuznetsovii[207], D. thermocisternum[180], D. thermosapovorans[212], D. thermolithotrophum[216], D. australicum[178], D. rhabdoformis[396], Thermotoga subterranea[281] 
 Hydrogen from an organic source:T. modestius[259], P. islandicum[346], Pyrodictium abyssi[352], Thermotoga elfii[279], Thermotoga hypogea[280] 
C11 As written:D. sulfodismutans [397, 398
C12 As written:Thiobacillus tepidarius, T. neapolitanus[87] 
C13 As written:T. tepidarius, T. neapolitanus[87] 
C14 As written:T. neapolitanus[381], T. chilensis[403], T. hydrothermalis[401], T. azorensis[276], Sulfolobus hakonensis[316], T. tepidarius[87] 
C15 Hydrogen from an organic source:Bacterium paratyphosum B [405] 
C16 As written:T. thioparus[381], T. thiooxidans, T. ferrooxidans[387], A. pyrophilus[82], A. infernus, A. brierleyi[292], Acidianus ambivalens [289–291], M. sedula[297], M. prunae[296], S. acidocaldarius[313], S. solfataricus[320], S. metallicus[317], Sulfolobacillus thermosulfidooxidans[246], Sulfobacillus acidophilus[245], S. shibatae [318, 319], S. hakonensis[316], S. yellowstonii[322], Sulfurococcus mirabilis[321], T. thiopara [277, 278], T. azorensis[276], T. prosperus[406], T. hydrothermalis[401], T. chilensis[403], T. crunogena[402], Beggiatoa [407–409], Thiovulum[409] 
C17 As written:D. sulfoexigens[399], D. thiozymogenes, Desulfobulbus propionicus[400] 
C18 As written:T. thiooxidans, T. thioparus[381] 
C19 As written:P. occultum, P. brockii[353], A. infernus, A. brierleyi[292], A. degensii[187], T. tenax [375, 377], Thermoproteus neutrophilus, T. maritimus[375], P. islandicum[346], A. pyrophilus[82], A. ambivalens [289–291], Desulfurella kamchatkensis, Desulfurella propionica[214], D. thermolithotrophum[216], Hyperthermus butylicus[338], Stetteria hydrogenophila[355],Stygiolobus azoricus[312], S. arcachonense[380] 
 Hydrogen from an organic source:Thermococcus litoralis [368, 369], Thermococcus zilligii [323, 324], Thermococcus alcaliphilus[360], Pyrobaculum organotrophum[346], Thermoproteus uzoniensis[378], Thermoplasma acidophilum, T. volcanium[325], Thermofilum pendens[376], Pyrococcus woesei[351], Thermococcus profundus[371], Thermococcus celer[363], Desulfurococcus mucosus, Desulfurococcus mobilis[337], Thermococcus stetteri[373], Pyrococcus abyssi[347], Pyrococcus furiosus[349], Pyrococcus horikoshii[350], P. abyssi[352], T. modestius[259], Thermococcus acidaminovorans[358], Thermococcus guaymasensis, Thermococcus aggregans[359], Thermococcus chitonophagus[364], Thermococcus barossii[362], Thermococcus fumicolans[365], Thermococcus gorgonarius[366], Thermococcus hydrothermalis[367], Thermococcus pacificus[214], Thermococcus siculi[372], Thermosipho africanus[273], T. maritima[287], Thermotoga neapolitana[288], Desulfurococcus amylolyticus[336], Staphylothermus marinus[354] 
C20 As written:Thiovulum, Beggiatoa[409], T. chilensis[403], T. hydrothermalis[401], Thiobacillus propserus[406], T. crunogena[402], T. azorensis[276], S. hakonensis[316], T. thioparus[410] 
C21 As written:T. thioparus[410] 
C22 As written:T. thioparus[410], Thiovulum[409], Beggiatoa [407–409
Reaction  
C1 As written:Archaeoglobus lithotrophicus[37], Desulfotomaculum auripigmentum[393], Desulfacinum infernum[206], Desulfonatronum lacustre[394], Thermodesulfobacterium mobile[265], Thermodesulfobacterium commune[263], Desulfotomaculum putei[175], Desulfotomaculum luciae [175, 208], Archaeoglobus profundus[331], Thermodesulfovibrio yellowstonii[267], Desulfotomaculum kuznetsovii[207], Desulfotomaculum geothermicum[35], Desulfonatronovibrio hydrogenovorans[395], Desulfotomaculum thermocisternum[180], Desulfotomaculum thermosapovorans[212], A. degensii[187], Desulfotomaculum australicum[170], Desulfotomaculum halophilum[178], Desulfobulbus rhabdoformis[396], D. desulfuricans[381], Desulfotomaculum thermoacetoxidans[210] 
 Hydrogen from an organic source:Archaeoglobus fulgidus [328–330], Thermocladium modestius[259] 
C2 As written:Desulfovibrio sulfodismutans [397, 398], Desulfocapsa sulfoexigens[399], Desulfocapsa thiozymogenes[400] 
C3 As written:D. desulfuricans[381], D. infernum[206], D. lacustre[394], A. veneficus[295], D. putei[175], A. profundus[331], T. yellowstonii[267], D. kuznetsovii[207], D. hydrogenovorans[395], D. thermocisternum[180], D. thermosapovorans[212], D. halophilum[178], D. rhabdoformis[396], Desulfurobacterium thermolithotrophum[216], Pyrodictium brockii[352] 
 Hydrogen from an organic source:A. fulgidus [328–330], Pyrobaculum islandicum[346] 
C4 As written:Thiobacillus thiooxidans, T. thioparus[381] 
C5 As written:Thiobacillus novellus[381], A. pyrophilus[82], P. aerophilum[345], Thermothrix azorensis[276], T. thiopara [277, 278], Thiobacillus hydrothermalis[401], Thiomicrospira crunogena[402], Thiomicrospira chilensis[403] 
C6 As written:Thiobacillus neapolitanus[381] 
C7 As written:T. thioparus[381] 
C8 As written:D. sulfodismutans [397, 398], D. sulfoexigens[399], D. thiozymogenes[400], D. hydrogenovorans[395] 
C9 As written: purple and green photosynthetic Bacteria [404] 
C10 As written:A. fulgidus[329], D. infernum[206], F. placidus[84], D. lacustre[394], P. occultum[352], A. veneficus[295], D. putei[175], D. luciae [175, 208], A. profundus[331], T. yellowstonii[267], D. kuznetsovii[207], D. thermocisternum[180], D. thermosapovorans[212], D. thermolithotrophum[216], D. australicum[178], D. rhabdoformis[396], Thermotoga subterranea[281] 
 Hydrogen from an organic source:T. modestius[259], P. islandicum[346], Pyrodictium abyssi[352], Thermotoga elfii[279], Thermotoga hypogea[280] 
C11 As written:D. sulfodismutans [397, 398
C12 As written:Thiobacillus tepidarius, T. neapolitanus[87] 
C13 As written:T. tepidarius, T. neapolitanus[87] 
C14 As written:T. neapolitanus[381], T. chilensis[403], T. hydrothermalis[401], T. azorensis[276], Sulfolobus hakonensis[316], T. tepidarius[87] 
C15 Hydrogen from an organic source:Bacterium paratyphosum B [405] 
C16 As written:T. thioparus[381], T. thiooxidans, T. ferrooxidans[387], A. pyrophilus[82], A. infernus, A. brierleyi[292], Acidianus ambivalens [289–291], M. sedula[297], M. prunae[296], S. acidocaldarius[313], S. solfataricus[320], S. metallicus[317], Sulfolobacillus thermosulfidooxidans[246], Sulfobacillus acidophilus[245], S. shibatae [318, 319], S. hakonensis[316], S. yellowstonii[322], Sulfurococcus mirabilis[321], T. thiopara [277, 278], T. azorensis[276], T. prosperus[406], T. hydrothermalis[401], T. chilensis[403], T. crunogena[402], Beggiatoa [407–409], Thiovulum[409] 
C17 As written:D. sulfoexigens[399], D. thiozymogenes, Desulfobulbus propionicus[400] 
C18 As written:T. thiooxidans, T. thioparus[381] 
C19 As written:P. occultum, P. brockii[353], A. infernus, A. brierleyi[292], A. degensii[187], T. tenax [375, 377], Thermoproteus neutrophilus, T. maritimus[375], P. islandicum[346], A. pyrophilus[82], A. ambivalens [289–291], Desulfurella kamchatkensis, Desulfurella propionica[214], D. thermolithotrophum[216], Hyperthermus butylicus[338], Stetteria hydrogenophila[355],Stygiolobus azoricus[312], S. arcachonense[380] 
 Hydrogen from an organic source:Thermococcus litoralis [368, 369], Thermococcus zilligii [323, 324], Thermococcus alcaliphilus[360], Pyrobaculum organotrophum[346], Thermoproteus uzoniensis[378], Thermoplasma acidophilum, T. volcanium[325], Thermofilum pendens[376], Pyrococcus woesei[351], Thermococcus profundus[371], Thermococcus celer[363], Desulfurococcus mucosus, Desulfurococcus mobilis[337], Thermococcus stetteri[373], Pyrococcus abyssi[347], Pyrococcus furiosus[349], Pyrococcus horikoshii[350], P. abyssi[352], T. modestius[259], Thermococcus acidaminovorans[358], Thermococcus guaymasensis, Thermococcus aggregans[359], Thermococcus chitonophagus[364], Thermococcus barossii[362], Thermococcus fumicolans[365], Thermococcus gorgonarius[366], Thermococcus hydrothermalis[367], Thermococcus pacificus[214], Thermococcus siculi[372], Thermosipho africanus[273], T. maritima[287], Thermotoga neapolitana[288], Desulfurococcus amylolyticus[336], Staphylothermus marinus[354] 
C20 As written:Thiovulum, Beggiatoa[409], T. chilensis[403], T. hydrothermalis[401], Thiobacillus propserus[406], T. crunogena[402], T. azorensis[276], S. hakonensis[316], T. thioparus[410] 
C21 As written:T. thioparus[410] 
C22 As written:T. thioparus[410], Thiovulum[409], Beggiatoa [407–409

As noted above, numerous thermophiles and hyperthermophiles gain metabolic energy by oxidizing or reducing sulfur compounds. One of these is Pyrodictium occultum, a hyperthermophilic chemolithoautotrophic Archaeon isolated from shallow marine hot springs in the Baia di Levante on Vulcano, Italy [47]. P. occultum was the first organism in pure culture able to grow at temperatures above 100°C, gaining metabolic energy by reducing elemental sulfur with H2 and producing H2S (Reaction C19). Several other genera of thermophiles and hyperthermophiles (see Table 6.4), both autotrophic and heterotrophic, include species that are known to catalyze this reduction reaction, including Acidianus, Thermococcus, Pyrococcus, Hyperthermus, Pyrobaculum, Thermoplasma, and Staphylothermus.

Values of ΔGC19 as functions of aH2 and aH2S representative of many hydrothermal systems are shown in Fig. 12. These values were calculated at 25, 55, 100, and 150°C with Eq. 5 as described above. It can be seen in Fig. 12 that at constant values of aH2S, values of ΔGC19 decrease with increasing values of aH2 at any temperature investigated; the decrease of ΔGC19 is more precipitous at high rather than at low temperatures. In other words, values of ΔGC19 increase with increasing temperature at low values of aH2, but decrease with increasing temperature at higher values of aH2. Conversely, at constant values of aH2, values of ΔGC19 increase with increasing values of aH2S at any temperature investigated, increasing more dramatically at high than at low temperatures. The net effect of the complex dependence of ΔGC19 on temperature, aH2, and aH2S is that organisms such as P. occultum can obtain the most metabolic energy from Reaction (C19) at high temperatures, high activities of H2, and low activities of H2S. The lowest amount of energy is available at high temperatures, high activities of H2S, and low activities of H2. Observations of this type, coupled with appropriate chemical analyses, should help to explain the occurrence of P. occultum in some hydrothermal systems but not in others.

Figure 12

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction (C19) as a function of log aH2S and log aH2. The activity of H2O(l) is taken to be unity.

Figure 12

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction (C19) as a function of log aH2S and log aH2. The activity of H2O(l) is taken to be unity.

The H–O–N–S system

Metabolic processes are discussed above in which the reduction (by H2) and oxidation (by O2) of various nitrogen (Table 5.2) or sulfur compounds (Table 6.2) provide energy for microorganisms. Additional metabolic processes are known in which the oxidation of sulfur is coupled to the reduction of nitrogen. Five such reactions in which NO3 serves as the electron acceptor and thiosulfate, sulfur, or sulfide as the electron donor are listed in Table 6.5; the corresponding values of ΔGr° as a function of temperature are reported in Table 6.6. All five of these reactions are known to be carried out by thermophiles or hyperthermophiles, including, for example, T. thiopara, a facultatively anaerobic facultative chemolithoautotroph isolated from a pH-neutral, sulfide-rich, 74°C hot spring in New Mexico. In the laboratory under anaerobic conditions at temperatures between 62 and 77°C, T. thiopara can gain metabolic energy from Reactions (C23) and (C25)–(C27). Other microbes experimentally verified to mediate the sulfur–nitrogen redox couples shown in Table 6.5 are listed in Table 6.7, including the hyperthermophiles Pyrobaculum, Aquifex, and Ferroglobus. Given the substantial variety in oxidation states of inorganic sulfur and nitrogen compounds, it is very likely that the reactions listed in Table 6.5 are only a subset of the sulfur–nitrogen redox reactions used by microorganisms.

Table 6.5

Mixed metabolic reactions involving S, N, H and O compounds

C23 5S2O32−+8NO3+H2O(l)↔10SO42−+4N2(aq)+2H+ 
C24 5S(s)+6NO3+2H2O(l)↔5SO42−+3N2(aq)+4H+ 
C25 NO3+H2S(aq)↔NO2+H2O(l)+S(s) 
C26 2NO3+5H2S(aq)+2H+↔N2(aq)+5S(s)+6H2O(l) 
C27 8NO3+5H2S(aq)↔4N2(aq)+5SO42−+4H2O(l)+2H+ 
C23 5S2O32−+8NO3+H2O(l)↔10SO42−+4N2(aq)+2H+ 
C24 5S(s)+6NO3+2H2O(l)↔5SO42−+3N2(aq)+4H+ 
C25 NO3+H2S(aq)↔NO2+H2O(l)+S(s) 
C26 2NO3+5H2S(aq)+2H+↔N2(aq)+5S(s)+6H2O(l) 
C27 8NO3+5H2S(aq)↔4N2(aq)+5SO42−+4H2O(l)+2H+ 
Table 6.6

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 6.5

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
C23 −3657.59 −3641.55 −3634.49 −3622.38 −3614.29 −3604.17 −3588.98 −3573.76 −3558.52 −3543.23 −3507.25 −3454.68 
C24 −2545.80 −2533.47 −2527.93 −2518.22 −2511.64 −2503.29 −2490.51 −2477.45 −2464.06 −2450.32 −2416.33 −2363.73 
C25 −131.56 −130.90 −130.57 −129.98 −129.55 −128.99 −128.11 −127.17 −126.19 −125.18 −122.78 −119.06 
C26 −1049.22 −1045.22 −1043.48 −1040.52 −1038.60 −1036.14 −1032.50 −1028.97 −1025.48 −1022.12 −1015.15 −1006.61 
C27 −3595.02 −3578.69 −3571.40 −3558.75 −3550.24 −3539.43 −3523.02 −3506.42 −3489.54 −3472.43 −3431.48 −3370.35 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
C23 −3657.59 −3641.55 −3634.49 −3622.38 −3614.29 −3604.17 −3588.98 −3573.76 −3558.52 −3543.23 −3507.25 −3454.68 
C24 −2545.80 −2533.47 −2527.93 −2518.22 −2511.64 −2503.29 −2490.51 −2477.45 −2464.06 −2450.32 −2416.33 −2363.73 
C25 −131.56 −130.90 −130.57 −129.98 −129.55 −128.99 −128.11 −127.17 −126.19 −125.18 −122.78 −119.06 
C26 −1049.22 −1045.22 −1043.48 −1040.52 −1038.60 −1036.14 −1032.50 −1028.97 −1025.48 −1022.12 −1015.15 −1006.61 
C27 −3595.02 −3578.69 −3571.40 −3558.75 −3550.24 −3539.43 −3523.02 −3506.42 −3489.54 −3472.43 −3431.48 −3370.35 
Table 6.7

Microorganisms that use the reactions specified in Table 6.5

Reaction  
C23 T. denitrificans[381], P. aerophilum[345], A. pyrophilus[82], T. thioparus [277, 278
C24 T. denitrificans[381], A. pyrophilus[82], Thioploca chileae, Thioploca araucae[411] 
C25 F. placidus[84], T. thioparus [277, 278
C26 T. chileae, T. araucae[411], T. thioparus [277, 278
C27 T. chileae, T. araucae[411], T. thioparus [277, 278
Reaction  
C23 T. denitrificans[381], P. aerophilum[345], A. pyrophilus[82], T. thioparus [277, 278
C24 T. denitrificans[381], A. pyrophilus[82], Thioploca chileae, Thioploca araucae[411] 
C25 F. placidus[84], T. thioparus [277, 278
C26 T. chileae, T. araucae[411], T. thioparus [277, 278
C27 T. chileae, T. araucae[411], T. thioparus [277, 278

The H–O–Cinorganic system

For the purpose of this review, we have grouped several carbon compounds that can have abiotic sources in the H–O–Cinorganic system including CH4 and hydrogen cyanide (HCN). Values of ΔG° as a function of temperature for ‘inorganic’ carbon species, including several containing N or S, are given in Table 7.1. Nine Reactions among these molecules known to be mediated by microorganisms and values of ΔGr° as a function of temperature for these Reactions are given in Tables 7.2 and 7.3, respectively.

Table 7.1

Values of ΔG° (kJ mol−1) at PSAT as a function of temperature for inorganic compounds in the system H–O–N–S–Cinorganic

Compounds T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
CO2(g) −389.48 −392.87 −394.36 −396.93 −398.66 −400.83 −404.10 −407.40 −410.73 −414.08 −421.99 −433.51 
CO2(aq) −383.51 −385.17 −385.98 −387.44 −388.48 −389.84 −391.99 −394.26 −396.66 −399.17 −405.42 −415.22 
CO3−2 −528.83 −528.31 −527.98 −527.32 −526.81 −526.10 −524.91 −523.56 −522.07 −520.43 −515.98 −507.92 
HCO3 −584.63 −586.25 −586.94 −588.12 −588.89 −589.86 −591.29 −592.71 −594.11 −595.49 −598.61 −602.71 
COS(g) −160.36 −164.03 −165.64 −168.43 −170.30 −172.65 −176.20 −179.77 −183.38 −187.01 −195.59 −208.07 
CO(g) −132.65 −135.79 −137.17 −139.55 −141.14 −143.14 −146.16 −149.19 −152.25 −155.32 −162.56 −173.04 
CO(aq) −117.91 −119.31 −120.01 −121.30 −122.23 −123.45 −125.42 −127.52 −129.76 −132.13 −138.11 −147.70 
CN 174.63 173.04 172.38 171.26 170.54 169.65 168.34 167.06 165.82 164.62 161.95 158.65 
HCN(aq) 122.36 120.52 119.66 118.12 117.06 115.68 113.54 111.30 108.97 106.57 100.65 91.55 
OCN −94.88 −96.65 −97.41 −98.67 −99.50 −100.52 −102.04 −103.52 −104.96 −106.38 −109.55 −113.62 
SCN 96.08 93.73 92.71 90.99 89.85 88.43 86.32 84.22 82.14 80.08 75.36 68.97 
CH4(g) −46.47 −49.42 −50.72 −52.97 −54.47 −56.36 −59.22 −62.10 −65.02 −67.95 −74.89 −85.01 
CH4(aq) −32.71 −33.87 −34.46 −35.57 −36.38 −37.47 −39.23 −41.12 −43.17 −45.34 −50.87 −59.83 
Compounds T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
CO2(g) −389.48 −392.87 −394.36 −396.93 −398.66 −400.83 −404.10 −407.40 −410.73 −414.08 −421.99 −433.51 
CO2(aq) −383.51 −385.17 −385.98 −387.44 −388.48 −389.84 −391.99 −394.26 −396.66 −399.17 −405.42 −415.22 
CO3−2 −528.83 −528.31 −527.98 −527.32 −526.81 −526.10 −524.91 −523.56 −522.07 −520.43 −515.98 −507.92 
HCO3 −584.63 −586.25 −586.94 −588.12 −588.89 −589.86 −591.29 −592.71 −594.11 −595.49 −598.61 −602.71 
COS(g) −160.36 −164.03 −165.64 −168.43 −170.30 −172.65 −176.20 −179.77 −183.38 −187.01 −195.59 −208.07 
CO(g) −132.65 −135.79 −137.17 −139.55 −141.14 −143.14 −146.16 −149.19 −152.25 −155.32 −162.56 −173.04 
CO(aq) −117.91 −119.31 −120.01 −121.30 −122.23 −123.45 −125.42 −127.52 −129.76 −132.13 −138.11 −147.70 
CN 174.63 173.04 172.38 171.26 170.54 169.65 168.34 167.06 165.82 164.62 161.95 158.65 
HCN(aq) 122.36 120.52 119.66 118.12 117.06 115.68 113.54 111.30 108.97 106.57 100.65 91.55 
OCN −94.88 −96.65 −97.41 −98.67 −99.50 −100.52 −102.04 −103.52 −104.96 −106.38 −109.55 −113.62 
SCN 96.08 93.73 92.71 90.99 89.85 88.43 86.32 84.22 82.14 80.08 75.36 68.97 
CH4(g) −46.47 −49.42 −50.72 −52.97 −54.47 −56.36 −59.22 −62.10 −65.02 −67.95 −74.89 −85.01 
CH4(aq) −32.71 −33.87 −34.46 −35.57 −36.38 −37.47 −39.23 −41.12 −43.17 −45.34 −50.87 −59.83 
Table 7.2

Inorganic carbon metabolic reactions

D1 CO2(aq)+4H2(aq)↔CH4(aq)+2H2O(l) 
D2 COS(g)+2O2(aq)+H2O(l)↔SO42−+CO2(aq)+2H+ 
D3 COS(g)+H2O(l)↔CO2(aq)+H2S(aq) 
D4 CO(aq)+0.5O2(aq)↔CO2(aq) 
D5 4CO(aq)+2H2O(l)↔CH4(aq)+3CO2(aq) 
D6 CO(aq)+3H2(aq)↔CH4(aq)+H2O(l) 
D7 SCN+2O2(aq)+2H2O(l)↔SO42−+CO2(aq)+NH4+ 
D8 SCN+H2O(l)↔H2S(aq)+OCN 
D9 CH4(aq)+2O2(aq)↔CO2(aq)+2H2O(l) 
D1 CO2(aq)+4H2(aq)↔CH4(aq)+2H2O(l) 
D2 COS(g)+2O2(aq)+H2O(l)↔SO42−+CO2(aq)+2H+ 
D3 COS(g)+H2O(l)↔CO2(aq)+H2S(aq) 
D4 CO(aq)+0.5O2(aq)↔CO2(aq) 
D5 4CO(aq)+2H2O(l)↔CH4(aq)+3CO2(aq) 
D6 CO(aq)+3H2(aq)↔CH4(aq)+H2O(l) 
D7 SCN+2O2(aq)+2H2O(l)↔SO42−+CO2(aq)+NH4+ 
D8 SCN+H2O(l)↔H2S(aq)+OCN 
D9 CH4(aq)+2O2(aq)↔CO2(aq)+2H2O(l) 
Table 7.3

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 7.2

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
D1 −196.02 −194.53 −193.73 −192.17 −191.01 −189.45 −186.87 −184.04 −180.98 −177.69 −169.22 −155.32 
D2 −768.89 −763.32 −760.69 −755.96 −752.66 −748.38 −741.67 −734.62 −727.25 −719.57 −700.41 −669.86 
D3 −12.72 −11.51 −11.07 −10.44 −10.10 −9.73 −9.33 −9.08 −8.96 −8.98 −9.47 −11.15 
D4 −275.01 −274.50 −274.24 −273.73 −273.36 −272.86 −272.04 −271.14 −270.17 −269.13 −266.44 −261.93 
D5 −240.31 −238.73 −237.99 −236.62 −235.65 −234.38 −232.36 −230.21 −227.92 −225.51 −219.35 −209.28 
D6 −207.10 −205.59 −204.79 −203.28 −202.17 −200.68 −198.25 −195.59 −192.72 −189.64 −181.75 −168.81 
D7 −866.64 −863.06 −861.32 −858.14 −855.90 −852.95 −848.28 −843.31 −838.06 −832.52 −818.55 −795.92 
D8 19.47 19.26 19.14 18.91 18.73 18.50 18.11 17.68 17.22 16.72 15.45 13.40 
D9 −859.72 −859.28 −858.97 −858.31 −857.79 −857.05 −855.80 −854.36 −852.77 −851.03 −846.39 −838.43 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
D1 −196.02 −194.53 −193.73 −192.17 −191.01 −189.45 −186.87 −184.04 −180.98 −177.69 −169.22 −155.32 
D2 −768.89 −763.32 −760.69 −755.96 −752.66 −748.38 −741.67 −734.62 −727.25 −719.57 −700.41 −669.86 
D3 −12.72 −11.51 −11.07 −10.44 −10.10 −9.73 −9.33 −9.08 −8.96 −8.98 −9.47 −11.15 
D4 −275.01 −274.50 −274.24 −273.73 −273.36 −272.86 −272.04 −271.14 −270.17 −269.13 −266.44 −261.93 
D5 −240.31 −238.73 −237.99 −236.62 −235.65 −234.38 −232.36 −230.21 −227.92 −225.51 −219.35 −209.28 
D6 −207.10 −205.59 −204.79 −203.28 −202.17 −200.68 −198.25 −195.59 −192.72 −189.64 −181.75 −168.81 
D7 −866.64 −863.06 −861.32 −858.14 −855.90 −852.95 −848.28 −843.31 −838.06 −832.52 −818.55 −795.92 
D8 19.47 19.26 19.14 18.91 18.73 18.50 18.11 17.68 17.22 16.72 15.45 13.40 
D9 −859.72 −859.28 −858.97 −858.31 −857.79 −857.05 −855.80 −854.36 −852.77 −851.03 −846.39 −838.43 

Under aerobic conditions, CO and CH4 can be oxidized to CO2 (reactions D4 and D9, respectively) by a variety of organisms including members of the genera Bacillus, Pseudomonas, Alcaligenes, and Methylococcus. Reduction (reaction D6) and disproportionation (Reaction D5) of CO producing CH4 can be mediated by Methanobacterium. Some Thiobacillus thioparus and Paracoccus strains oxidize organosulfur compounds such as carbonyl sulfide or thiocyanate to sulfate and CO2 (Reactions D2 and D7, respectively) to gain metabolic energy [87]. These strains can also hydrolyze carbonyl sulfide (Reaction D3) and thiocyanate (Reaction D8) yielding H2S and either CO2 or OCN, respectively [87]. It should be noted that values of ΔGr° over the temperature range considered here (Table 7.3) for the two hydrolysis Reactions are much greater (less negative or even positive) than those of their oxidation counterparts.

Of the reactions listed in Table 7.2, autotrophic methanogenesis from CO2 and H2 (Reaction D1) is by far the most common and also one of the best characterized of all metabolic processes in thermophiles [8, 88–93]. Species belonging to at least six genera are able to carry out this mode of autotrophic methanogenesis, including a significant number of thermophiles and hyperthermophiles. As an example, Methanopyrus kandleri, isolated from heated deep sea sediments in the Guaymas Basin and from a shallow marine hydrothermal system on Iceland [94], grows on metabolic energy gained from reaction (D1) at temperatures up to 110°C. Many microorganisms responsible for conducting the reactions given in Table 7.2 are listed in Table 7.4.

Table 7.4

Microorganisms that use the carbon reactions specified in Table 7.2

Reaction  
D1 As written:Methanococcus vannielii, M. barkeri[387],Methanobacterium wolfei, Methanobacterium alcaliphilum[391], M. thermolithotrophicus[302], M. jannaschii[126],M. kandleri[94], Methanococcus CS-1 [165], Methanococcus fervens (AG86)[303, 339], Methanobacterium thermoautotrophicus[306], Methanothermus fervidus[343], Methanothermus sociabilis[344], Methanococcus igneus[340], Methanobacterium thermoalcaliphilum[300], Methanobacterium thermoaggregans[299], Methanocalculus halotolerans[412], Methanobacterium thermoflexum, Methanobacterium defluvii[298], Methanobacterium subterraneum[43], Methanococcus infernus[341], Methanococcus vulcanius[303], Methanoplanus petrolearius[413] 
D2 As written:T. thioparus, Paracoccus[87] 
D3 As written:T. thioparus, Paracoccus[87] 
D4 As written:B. schlegelii, Pseudomonas carboxydovorans, Alcaligenes carboxydus[387] 
D5 As written:Methanobacterium thermoautotrophicum[387] 
D6 As written:Methanobacterium formicicum[381] 
D7 As written:T. thioparus, Paracoccus[87] 
D8 As written:T. thioparus, Paracoccus[87] 
D9 As written:Methylococcus thermophilus[233] 
Reaction  
D1 As written:Methanococcus vannielii, M. barkeri[387],Methanobacterium wolfei, Methanobacterium alcaliphilum[391], M. thermolithotrophicus[302], M. jannaschii[126],M. kandleri[94], Methanococcus CS-1 [165], Methanococcus fervens (AG86)[303, 339], Methanobacterium thermoautotrophicus[306], Methanothermus fervidus[343], Methanothermus sociabilis[344], Methanococcus igneus[340], Methanobacterium thermoalcaliphilum[300], Methanobacterium thermoaggregans[299], Methanocalculus halotolerans[412], Methanobacterium thermoflexum, Methanobacterium defluvii[298], Methanobacterium subterraneum[43], Methanococcus infernus[341], Methanococcus vulcanius[303], Methanoplanus petrolearius[413] 
D2 As written:T. thioparus, Paracoccus[87] 
D3 As written:T. thioparus, Paracoccus[87] 
D4 As written:B. schlegelii, Pseudomonas carboxydovorans, Alcaligenes carboxydus[387] 
D5 As written:Methanobacterium thermoautotrophicum[387] 
D6 As written:Methanobacterium formicicum[381] 
D7 As written:T. thioparus, Paracoccus[87] 
D8 As written:T. thioparus, Paracoccus[87] 
D9 As written:Methylococcus thermophilus[233] 

Values of the overall Gibbs free energy for autotrophic methanogenesis from CO2GD1) were calculated in accord with Eq. 5 at 25, 55, 100, and 150°C and are shown in Figs. 13–15. In these figures, constructed for activities of H2 equal to 10−3 (Fig. 13), 10−5 (Fig. 14), and 10−7 (Fig. 15), values of ΔGD1 are depicted as contours relative to the activities of CH4 and CO2 that range from 10−10 to 0. It can be seen in these figures that ΔGD1 is negative at most conditions considered here, increasing towards less exergonic values with increasing temperature at constant activities of H2, CO2, and CH4. Reaction (D1) is endergonic only at elevated temperatures in combination with high activities of CH4 or low activities of CO2 and H2. For example, at representative activities of CH4, H2, and CO2 in hydrothermal systems equal to 10−6, 10−5, and 10−4, respectively, and at a temperature of 100°C (see Fig. 14), close to the optimum laboratory growth temperature of M. kandleri, ΔGD1 is equal to −55 kJ mol−1. Although numerous obligately autotrophic thermophiles, including M. kandleri, have been isolated from hydrothermal ecosystems, the majority of thermophiles currently in culture are obligate heterotrophs [8].

Figure 13

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction (D1) as a function of log aCH4 and log aCO2. The activity of H2(aq) is set at 10−3, and the activity of H2O(l) is taken to be unity.

Figure 13

Plots of ΔGr (represented as solid contours) at PSAT and 25, 55, 100, and 150°C for Reaction (D1) as a function of log aCH4 and log aCO2. The activity of H2(aq) is set at 10−3, and the activity of H2O(l) is taken to be unity.

Figure 14

Same as for Fig. 13, except that the activity of H2(aq) is set at 10−5.

Figure 14

Same as for Fig. 13, except that the activity of H2(aq) is set at 10−5.

Figure 15

Same as for Fig. 13, except that the activity of H2(aq) is set at 10−7.

Figure 15

Same as for Fig. 13, except that the activity of H2(aq) is set at 10−7.

The H–O–C, H–O–N–C, H–O–S–C, and H–O–N–S–Camino acid systems

In laboratory growth studies, thermophilic heterotrophs commonly utilize complex organic molecules such as proteinaceous materials and carbohydrates as carbon and energy sources. In nature, however, the molecular identities of the requisite organic compounds remain obscure. Owing to an incomplete data set for the thermodynamic properties of aqueous sugars, peptides, nucleic acid bases, and vitamins at elevated temperatures, together with an alarming shortage of organic analyses from hydrothermal systems where heterotrophic thermophiles are known to thrive, only a limited number of heterotrophic metabolic reaction types could be included in this study. It may seem at first glance that the plethora of organic compounds listed in Table 8.1 would be sufficient to characterize a significant fraction of overall heterotrophic metabolisms. This is not the case. Because of the dearth of thermodynamic and compositional data, we are limited to evaluating ΔGr° for heterotrophic reactions which involve predominantly organic acids, alcohols, or amino acids. The reactions and values of ΔGr° as a function of temperature in the system H–O–C are given in Tables 8.2 and 8.3, respectively. Analogous data are also given for the systems H–O–N–C (Tables 8.5 and 8.6), H–O–S–C (Tables 8.8 and 8.9), and H–O–N–S–Camino acid (Tables 8.11 and 8.12). Organisms known to carry out the reactions listed in Tables 8.2, 8.5, 8.8 and 8.11 are listed in Tables 8.4, 8.7, 8.10 and 8.13, respectively.

Table 8.1

Values of ΔG° (kJ mol−1) at PSAT as a function of temperature for aqueous and liquid organic compounds

Compound T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
Carboxylic acids 
Formate −348.69 −350.24 −350.88 −351.95 −352.65 −353.51 −354.78 −356.03 −357.26 −358.48 −361.21 −364.79 
Formic acid(aq) −368.64 −371.17 −372.30 −374.28 −375.62 −377.33 −379.96 −382.66 −385.44 −388.29 −395.22 −405.78 
Acetate −367.36 −368.72 −369.33 −370.37 −371.07 −371.96 −373.31 −374.69 −376.08 −377.49 −380.79 −385.40 
Acetic acid(aq) −392.52 −395.25 −396.48 −398.66 −400.17 −402.09 −405.08 −408.18 −411.40 −414.72 −422.88 −435.44 
Glycolate −504.47 −506.21 −506.98 −508.30 −509.19 −510.32 −512.03 −513.75 −515.51 −517.27 −521.43 −527.28 
Glycolic acid(aq) −524.89 −527.61 −528.86 −531.07 −532.59 −534.55 −537.60 −540.77 −544.07 −547.48 −555.90 −568.93 
Propanoate −360.66 −362.33 −363.09 −364.46 −365.40 −366.63 −368.55 −370.56 −372.66 −374.85 −380.23 −388.35 
Propanoic acid(aq) −386.48 −389.58 −391.00 −393.54 −395.30 −397.58 −401.15 −404.89 −408.80 −412.87 −422.96 −438.69 
Lactate −509.69 −511.75 −512.67 −514.30 −515.41 −516.85 −519.06 −521.35 −523.72 −526.15 −532.04 −540.80 
Lactic acid(aq) −530.19 −533.29 −534.72 −537.29 −539.07 −541.38 −544.99 −548.78 −552.74 −556.87 −567.09 −583.05 
Butanoic acid(aq) −376.55 −380.02 −381.63 −384.53 −386.54 −389.16 −393.26 −397.57 −402.09 −406.79 −418.48 −436.74 
Butanoate −351.28 −353.27 −354.18 −355.82 −356.97 −358.45 −360.79 −363.26 −365.84 −368.54 −375.20 −385.41 
Pentanoic acid(aq) −367.75 −371.59 −373.39 −376.64 −378.92 −381.89 −386.57 −391.52 −396.71 −402.15 −415.71 −437.02 
Pentanoate −342.31 −344.64 −345.73 −347.72 −349.13 −350.97 −353.91 −357.05 −360.37 −363.86 −372.63 −386.39 
Benzoate −207.58 −209.84 −210.88 −212.75 −214.05 −215.75 −218.41 −221.22 −224.17 −227.25 −234.86 −246.58 
Benzoic acid(aq) −229.90 −233.27 −234.86 −237.71 −239.71 −242.31 −246.40 −250.73 −255.29 −260.04 −271.92 −290.58 
Dicarboxylic acids 
Oxalate−2 −672.66 −673.70 −674.05 −674.52 −674.76 −674.99 −675.18 −675.22 −675.09 −674.80 −673.49 −669.86 
H–oxalate −694.80 −697.28 −698.34 −700.13 −701.31 −702.78 −704.94 −707.08 −709.18 −711.26 −715.97 −722.25 
Oxalic acid(aq) −701.44 −704.31 −705.59 −707.83 −709.34 −711.26 −714.21 −717.23 −720.32 −723.48 −731.11 −742.65 
Malonate−2 −683.68 −684.78 −685.18 −685.75 −686.07 −686.39 −686.72 −686.87 −686.83 −686.62 −685.36 −681.53 
H–malonate −713.55 −716.43 −717.69 −719.83 −721.25 −723.02 −725.68 −728.32 −730.96 −733.59 −739.65 −748.04 
Malonic acid(aq) −728.75 −732.35 −733.97 −736.80 −738.73 −741.19 −744.98 −748.88 −752.88 −756.99 −766.94 −782.03 
Succinate−2 −685.69 −687.18 −687.77 −688.70 −689.27 −689.92 −690.78 −691.49 −692.07 −692.50 −692.89 −691.75 
H–succinate −715.58 −718.59 −719.91 −722.18 −723.71 −725.64 −728.56 −731.52 −734.51 −737.51 −744.61 −754.76 
Succinic acid(aq) −738.13 −742.12 −743.92 −747.10 −749.28 −752.07 −756.37 −760.82 −765.41 −770.13 −781.64 −799.16 
Glutaric acid(aq) −732.86 −737.53 −739.66 −743.40 −745.96 −749.23 −754.30 −759.53 −764.92 −770.47 −783.99 −804.54 
H–glutarate −709.86 −713.34 −714.89 −717.56 −719.37 −721.66 −725.14 −728.69 −732.30 −735.95 −744.66 −757.38 
Glutarate−2 −681.28 −683.18 −683.97 −685.24 −686.05 −687.02 −688.38 −689.63 −690.76 −691.77 −693.64 −694.82 
Alcohols 
Methanol(aq) −172.98 −175.01 −175.94 −177.59 −178.74 −180.22 −182.53 −184.95 −187.47 −190.10 −196.61 −206.76 
Ethanol(aq) −178.08 −180.27 −181.30 −183.16 −184.47 −186.18 −188.90 −191.78 −194.83 −198.04 −206.10 −218.94 
Propanol(aq) −171.70 −174.18 −175.36 −177.52 −179.05 −181.07 −184.28 −187.72 −191.38 −195.25 −205.05 −220.76 
2-Propanol(aq) −182.37 −184.52 −185.56 −187.48 −188.86 −190.68 −193.62 −196.80 −200.21 −203.85 −213.17 −228.39 
Butanol(aq) −158.41 −161.18 −162.51 −164.97 −166.72 −169.03 −172.74 −176.72 −180.96 −185.46 −196.90 −215.35 
Pentanol(aq) −156.32 −159.45 −160.97 −163.77 −165.78 −168.42 −172.68 −177.27 −182.18 −187.38 −200.64 −222.10 
Alkanes 
Ethane(aq) −14.01 −15.51 −16.26 −17.68 −18.70 −20.08 −22.32 −24.77 −27.42 −30.26 −37.58 −49.58 
Propane(aq) −5.38 −7.28 −8.22 −9.99 −11.27 −12.97 −15.75 −18.78 −22.04 −25.52 −34.46 −49.04 
Butane(aq) 3.43 1.27 0.14 −2.00 −3.55 −5.64 −9.02 −12.69 −16.61 −20.80 −31.45 −48.67 
Pentane(aq) 12.83 10.24 8.90 6.37 4.53 2.08 −1.90 −6.19 −10.79 −15.67 −28.08 −48.10 
Octane(l)a 15.23 9.64 7.13 2.75 −0.24 −4.04 −9.89 −15.90 −22.09 −28.44 −43.88 −67.39 
Nonane(l)a 21.22 15.16 12.43 7.64 4.38 0.21 −6.20 −12.82 −19.63 −26.63 −43.69 −69.72 
Decane(l)a 27.22 20.66 17.71 12.53 8.99 4.48 −2.48 −9.66 −17.05 −24.65 −43.17 −71.45 
Undecane(l)a 33.23 26.18 23.00 17.42 13.61 8.75 1.26 −6.48 −14.45 −22.65 −42.64 −73.17 
Hexadecane(l)a 63.24 53.74 49.44 41.88 36.71 30.10 19.89 9.34 −1.54 −12.76 −40.15 −82.09 
Amino acids 
Alanine(aq) −367.97 −370.46 −371.59 −373.57 −374.93 −376.67 −379.38 −382.18 −385.08 −388.08 −395.45 −406.80 
Arginine(aq) −232.53 −237.68 −240.01 −244.09 −246.90 −250.49 −256.06 −261.84 −267.84 −274.04 −289.30 −312.88 
Arginine+ −284.86 −290.20 −292.60 −296.81 −299.69 −303.37 −309.06 −314.96 −321.07 −327.37 −342.81 −366.50 
Asparagine(aq) −519.57 −523.37 −525.06 −528.00 −530.00 −532.54 −536.47 −540.52 −544.71 −549.03 −559.59 −575.81 
Aspartic acid(aq) −716.56 −720.18 −721.79 −724.59 −726.51 −728.94 −732.70 −736.60 −740.62 −744.78 −754.97 −770.65 
Aspartate −695.24 −698.18 −699.44 −701.62 −703.09 −704.93 −707.74 −710.60 −713.51 −716.48 −723.57 −733.94 
Cysteine(aq) −331.80 −334.77 −336.11 −338.48 −340.11 −342.22 −345.50 −348.93 −352.51 −356.23 −365.44 −379.79 
Glutamic acid(aq) −718.30 −722.27 −724.05 −727.17 −729.30 −732.02 −736.23 −740.61 −745.13 −749.81 −761.29 −779.01 
Glutamate −695.38 −698.33 −699.62 −701.82 −703.31 −705.20 −708.08 −711.02 −714.03 −717.10 −724.48 −735.34 
Glutamine(aq) −522.50 −526.55 −528.36 −531.54 −533.72 −536.50 −540.81 −545.28 −549.92 −554.71 −566.48 −584.67 
Glycine(aq) −376.78 −379.39 −380.54 −382.52 −383.86 −385.54 −388.10 −390.71 −393.36 −396.05 −402.51 −412.17 
Histidine(aq) −196.45 −200.69 −202.60 −205.97 −208.29 −211.26 −215.87 −220.68 −225.68 −230.85 −243.61 −263.38 
Histidine+ −230.15 −234.67 −236.70 −240.26 −242.70 −245.81 −250.64 −255.65 −260.84 −266.21 −279.38 −299.64 
Isoleucine(aq) −338.63 −341.63 −343.05 −345.64 −347.46 −349.85 −353.62 −357.64 −361.89 −366.35 −377.57 −395.40 
Leucine(aq) −347.82 −350.86 −352.30 −354.93 −356.78 −359.20 −363.05 −367.15 −371.48 −376.05 −387.53 −405.81 
Lysine(aq) −332.23 −335.90 −337.58 −340.55 −342.60 −345.25 −349.39 −353.74 −358.27 −362.99 −374.70 −392.98 
Lysine+ −382.91 −386.87 −388.66 −391.83 −394.00 −396.80 −401.16 −405.71 −410.44 −415.35 −427.48 −446.28 
Methionine(aq) −496.85 −500.79 −502.59 −505.79 −508.00 −510.85 −515.29 −519.92 −524.75 −529.76 −542.10 −561.25 
Phenylalanine(aq) −201.72 −205.20 −206.83 −209.76 −211.82 −214.51 −218.76 −223.30 −228.09 −233.13 −245.85 −266.17 
Proline(aq) −303.13 −306.34 −307.78 −310.33 −312.07 −314.30 −317.75 −321.34 −325.04 −328.87 −338.26 −352.74 
Serine(aq) −514.03 −517.11 −518.49 −520.89 −522.53 −524.62 −527.84 −531.18 −534.63 −538.19 −546.91 −560.30 
Threonine(aq) −497.29 −500.10 −501.38 −503.65 −505.22 −507.26 −510.44 −513.79 −517.31 −520.97 −530.10 −544.42 
Tryptophan(aq) −106.79 −110.51 −112.23 −115.34 −117.54 −120.43 −125.05 −130.02 −135.34 −141.00 −155.48 −179.02 
Tyrosine(aq) −378.64 −382.39 −384.10 −387.16 −389.28 −392.01 −396.30 −400.81 −405.54 −410.46 −422.72 −441.93 
Valine(aq) −352.91 −355.72 −357.03 −359.39 −361.05 −363.20 −366.59 −370.18 −373.96 −377.91 −387.78 −403.37 
Miscellaneous 
Methanamine(aq) 23.88 21.96 21.08 19.51 18.43 17.02 14.83 12.52 10.12 7.61 1.38 −8.34 
Toluene(aq) 130.42 127.85 126.60 124.29 122.65 120.47 116.96 113.19 109.15 104.86 93.94 76.28 
Toluene(l) 122.76 119.56 118.11 115.58 113.85 111.63 108.23 104.70 101.08 97.34 88.23 74.29 
Ethylbenzene(aq) 140.05 137.13 135.72 133.10 131.23 128.76 124.80 120.53 115.98 111.16 98.92 79.24 
Ethylbenzene(l) 125.55 121.61 119.83 116.72 114.60 111.89 107.72 103.42 98.99 94.43 83.33 66.39 
Compound T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
Carboxylic acids 
Formate −348.69 −350.24 −350.88 −351.95 −352.65 −353.51 −354.78 −356.03 −357.26 −358.48 −361.21 −364.79 
Formic acid(aq) −368.64 −371.17 −372.30 −374.28 −375.62 −377.33 −379.96 −382.66 −385.44 −388.29 −395.22 −405.78 
Acetate −367.36 −368.72 −369.33 −370.37 −371.07 −371.96 −373.31 −374.69 −376.08 −377.49 −380.79 −385.40 
Acetic acid(aq) −392.52 −395.25 −396.48 −398.66 −400.17 −402.09 −405.08 −408.18 −411.40 −414.72 −422.88 −435.44 
Glycolate −504.47 −506.21 −506.98 −508.30 −509.19 −510.32 −512.03 −513.75 −515.51 −517.27 −521.43 −527.28 
Glycolic acid(aq) −524.89 −527.61 −528.86 −531.07 −532.59 −534.55 −537.60 −540.77 −544.07 −547.48 −555.90 −568.93 
Propanoate −360.66 −362.33 −363.09 −364.46 −365.40 −366.63 −368.55 −370.56 −372.66 −374.85 −380.23 −388.35 
Propanoic acid(aq) −386.48 −389.58 −391.00 −393.54 −395.30 −397.58 −401.15 −404.89 −408.80 −412.87 −422.96 −438.69 
Lactate −509.69 −511.75 −512.67 −514.30 −515.41 −516.85 −519.06 −521.35 −523.72 −526.15 −532.04 −540.80 
Lactic acid(aq) −530.19 −533.29 −534.72 −537.29 −539.07 −541.38 −544.99 −548.78 −552.74 −556.87 −567.09 −583.05 
Butanoic acid(aq) −376.55 −380.02 −381.63 −384.53 −386.54 −389.16 −393.26 −397.57 −402.09 −406.79 −418.48 −436.74 
Butanoate −351.28 −353.27 −354.18 −355.82 −356.97 −358.45 −360.79 −363.26 −365.84 −368.54 −375.20 −385.41 
Pentanoic acid(aq) −367.75 −371.59 −373.39 −376.64 −378.92 −381.89 −386.57 −391.52 −396.71 −402.15 −415.71 −437.02 
Pentanoate −342.31 −344.64 −345.73 −347.72 −349.13 −350.97 −353.91 −357.05 −360.37 −363.86 −372.63 −386.39 
Benzoate −207.58 −209.84 −210.88 −212.75 −214.05 −215.75 −218.41 −221.22 −224.17 −227.25 −234.86 −246.58 
Benzoic acid(aq) −229.90 −233.27 −234.86 −237.71 −239.71 −242.31 −246.40 −250.73 −255.29 −260.04 −271.92 −290.58 
Dicarboxylic acids 
Oxalate−2 −672.66 −673.70 −674.05 −674.52 −674.76 −674.99 −675.18 −675.22 −675.09 −674.80 −673.49 −669.86 
H–oxalate −694.80 −697.28 −698.34 −700.13 −701.31 −702.78 −704.94 −707.08 −709.18 −711.26 −715.97 −722.25 
Oxalic acid(aq) −701.44 −704.31 −705.59 −707.83 −709.34 −711.26 −714.21 −717.23 −720.32 −723.48 −731.11 −742.65 
Malonate−2 −683.68 −684.78 −685.18 −685.75 −686.07 −686.39 −686.72 −686.87 −686.83 −686.62 −685.36 −681.53 
H–malonate −713.55 −716.43 −717.69 −719.83 −721.25 −723.02 −725.68 −728.32 −730.96 −733.59 −739.65 −748.04 
Malonic acid(aq) −728.75 −732.35 −733.97 −736.80 −738.73 −741.19 −744.98 −748.88 −752.88 −756.99 −766.94 −782.03 
Succinate−2 −685.69 −687.18 −687.77 −688.70 −689.27 −689.92 −690.78 −691.49 −692.07 −692.50 −692.89 −691.75 
H–succinate −715.58 −718.59 −719.91 −722.18 −723.71 −725.64 −728.56 −731.52 −734.51 −737.51 −744.61 −754.76 
Succinic acid(aq) −738.13 −742.12 −743.92 −747.10 −749.28 −752.07 −756.37 −760.82 −765.41 −770.13 −781.64 −799.16 
Glutaric acid(aq) −732.86 −737.53 −739.66 −743.40 −745.96 −749.23 −754.30 −759.53 −764.92 −770.47 −783.99 −804.54 
H–glutarate −709.86 −713.34 −714.89 −717.56 −719.37 −721.66 −725.14 −728.69 −732.30 −735.95 −744.66 −757.38 
Glutarate−2 −681.28 −683.18 −683.97 −685.24 −686.05 −687.02 −688.38 −689.63 −690.76 −691.77 −693.64 −694.82 
Alcohols 
Methanol(aq) −172.98 −175.01 −175.94 −177.59 −178.74 −180.22 −182.53 −184.95 −187.47 −190.10 −196.61 −206.76 
Ethanol(aq) −178.08 −180.27 −181.30 −183.16 −184.47 −186.18 −188.90 −191.78 −194.83 −198.04 −206.10 −218.94 
Propanol(aq) −171.70 −174.18 −175.36 −177.52 −179.05 −181.07 −184.28 −187.72 −191.38 −195.25 −205.05 −220.76 
2-Propanol(aq) −182.37 −184.52 −185.56 −187.48 −188.86 −190.68 −193.62 −196.80 −200.21 −203.85 −213.17 −228.39 
Butanol(aq) −158.41 −161.18 −162.51 −164.97 −166.72 −169.03 −172.74 −176.72 −180.96 −185.46 −196.90 −215.35 
Pentanol(aq) −156.32 −159.45 −160.97 −163.77 −165.78 −168.42 −172.68 −177.27 −182.18 −187.38 −200.64 −222.10 
Alkanes 
Ethane(aq) −14.01 −15.51 −16.26 −17.68 −18.70 −20.08 −22.32 −24.77 −27.42 −30.26 −37.58 −49.58 
Propane(aq) −5.38 −7.28 −8.22 −9.99 −11.27 −12.97 −15.75 −18.78 −22.04 −25.52 −34.46 −49.04 
Butane(aq) 3.43 1.27 0.14 −2.00 −3.55 −5.64 −9.02 −12.69 −16.61 −20.80 −31.45 −48.67 
Pentane(aq) 12.83 10.24 8.90 6.37 4.53 2.08 −1.90 −6.19 −10.79 −15.67 −28.08 −48.10 
Octane(l)a 15.23 9.64 7.13 2.75 −0.24 −4.04 −9.89 −15.90 −22.09 −28.44 −43.88 −67.39 
Nonane(l)a 21.22 15.16 12.43 7.64 4.38 0.21 −6.20 −12.82 −19.63 −26.63 −43.69 −69.72 
Decane(l)a 27.22 20.66 17.71 12.53 8.99 4.48 −2.48 −9.66 −17.05 −24.65 −43.17 −71.45 
Undecane(l)a 33.23 26.18 23.00 17.42 13.61 8.75 1.26 −6.48 −14.45 −22.65 −42.64 −73.17 
Hexadecane(l)a 63.24 53.74 49.44 41.88 36.71 30.10 19.89 9.34 −1.54 −12.76 −40.15 −82.09 
Amino acids 
Alanine(aq) −367.97 −370.46 −371.59 −373.57 −374.93 −376.67 −379.38 −382.18 −385.08 −388.08 −395.45 −406.80 
Arginine(aq) −232.53 −237.68 −240.01 −244.09 −246.90 −250.49 −256.06 −261.84 −267.84 −274.04 −289.30 −312.88 
Arginine+ −284.86 −290.20 −292.60 −296.81 −299.69 −303.37 −309.06 −314.96 −321.07 −327.37 −342.81 −366.50 
Asparagine(aq) −519.57 −523.37 −525.06 −528.00 −530.00 −532.54 −536.47 −540.52 −544.71 −549.03 −559.59 −575.81 
Aspartic acid(aq) −716.56 −720.18 −721.79 −724.59 −726.51 −728.94 −732.70 −736.60 −740.62 −744.78 −754.97 −770.65 
Aspartate −695.24 −698.18 −699.44 −701.62 −703.09 −704.93 −707.74 −710.60 −713.51 −716.48 −723.57 −733.94 
Cysteine(aq) −331.80 −334.77 −336.11 −338.48 −340.11 −342.22 −345.50 −348.93 −352.51 −356.23 −365.44 −379.79 
Glutamic acid(aq) −718.30 −722.27 −724.05 −727.17 −729.30 −732.02 −736.23 −740.61 −745.13 −749.81 −761.29 −779.01 
Glutamate −695.38 −698.33 −699.62 −701.82 −703.31 −705.20 −708.08 −711.02 −714.03 −717.10 −724.48 −735.34 
Glutamine(aq) −522.50 −526.55 −528.36 −531.54 −533.72 −536.50 −540.81 −545.28 −549.92 −554.71 −566.48 −584.67 
Glycine(aq) −376.78 −379.39 −380.54 −382.52 −383.86 −385.54 −388.10 −390.71 −393.36 −396.05 −402.51 −412.17 
Histidine(aq) −196.45 −200.69 −202.60 −205.97 −208.29 −211.26 −215.87 −220.68 −225.68 −230.85 −243.61 −263.38 
Histidine+ −230.15 −234.67 −236.70 −240.26 −242.70 −245.81 −250.64 −255.65 −260.84 −266.21 −279.38 −299.64 
Isoleucine(aq) −338.63 −341.63 −343.05 −345.64 −347.46 −349.85 −353.62 −357.64 −361.89 −366.35 −377.57 −395.40 
Leucine(aq) −347.82 −350.86 −352.30 −354.93 −356.78 −359.20 −363.05 −367.15 −371.48 −376.05 −387.53 −405.81 
Lysine(aq) −332.23 −335.90 −337.58 −340.55 −342.60 −345.25 −349.39 −353.74 −358.27 −362.99 −374.70 −392.98 
Lysine+ −382.91 −386.87 −388.66 −391.83 −394.00 −396.80 −401.16 −405.71 −410.44 −415.35 −427.48 −446.28 
Methionine(aq) −496.85 −500.79 −502.59 −505.79 −508.00 −510.85 −515.29 −519.92 −524.75 −529.76 −542.10 −561.25 
Phenylalanine(aq) −201.72 −205.20 −206.83 −209.76 −211.82 −214.51 −218.76 −223.30 −228.09 −233.13 −245.85 −266.17 
Proline(aq) −303.13 −306.34 −307.78 −310.33 −312.07 −314.30 −317.75 −321.34 −325.04 −328.87 −338.26 −352.74 
Serine(aq) −514.03 −517.11 −518.49 −520.89 −522.53 −524.62 −527.84 −531.18 −534.63 −538.19 −546.91 −560.30 
Threonine(aq) −497.29 −500.10 −501.38 −503.65 −505.22 −507.26 −510.44 −513.79 −517.31 −520.97 −530.10 −544.42 
Tryptophan(aq) −106.79 −110.51 −112.23 −115.34 −117.54 −120.43 −125.05 −130.02 −135.34 −141.00 −155.48 −179.02 
Tyrosine(aq) −378.64 −382.39 −384.10 −387.16 −389.28 −392.01 −396.30 −400.81 −405.54 −410.46 −422.72 −441.93 
Valine(aq) −352.91 −355.72 −357.03 −359.39 −361.05 −363.20 −366.59 −370.18 −373.96 −377.91 −387.78 −403.37 
Miscellaneous 
Methanamine(aq) 23.88 21.96 21.08 19.51 18.43 17.02 14.83 12.52 10.12 7.61 1.38 −8.34 
Toluene(aq) 130.42 127.85 126.60 124.29 122.65 120.47 116.96 113.19 109.15 104.86 93.94 76.28 
Toluene(l) 122.76 119.56 118.11 115.58 113.85 111.63 108.23 104.70 101.08 97.34 88.23 74.29 
Ethylbenzene(aq) 140.05 137.13 135.72 133.10 131.23 128.76 124.80 120.53 115.98 111.16 98.92 79.24 
Ethylbenzene(l) 125.55 121.61 119.83 116.72 114.60 111.89 107.72 103.42 98.99 94.43 83.33 66.39 

aThermodynamic data for liquid n-alkanes are taken from Helgeson et al. (1998) [74].

Table 8.2

Metabolic reactions involving organic and inorganic carbon

E1 4H2(aq)+2CO2(aq)↔acetic acid(aq)+2H2O(l) 
E2 4formic acid(aq)↔CH4(aq)+3CO2(aq)+2H2O(l) 
E3 acetic acid(aq)+2O2(aq)↔2CO2(aq)+2H2O(l) 
E4 acetic acid(aq)↔CH4(aq)+CO2(aq) 
E5 propanoic acid(aq)+3.5O2(aq)↔3CO2(aq)+3H2O(l) 
E6 2lactic acid(aq)↔3acetic acid(aq) 
E7 2succinic acid(aq)+7O2(aq)↔8CO2(aq)+6H2O(l) 
E8 methanol(aq)+H2(aq)↔CH4(aq)+H2O(l) 
E9 4methanol(aq)↔3CH4(aq)+CO2(aq)+2H2O(l) 
E10 2ethanol(aq)+2CO2(aq)↔3acetic acid(aq) 
E11 2ethanol(aq)+CO2(aq)↔2acetic acid(aq)+CH4(aq) 
E12 4(2-)propanol(aq)+3CO2(aq)+2H2O(l)↔3CH4(aq)+4lactic acid(aq) 
E1 4H2(aq)+2CO2(aq)↔acetic acid(aq)+2H2O(l) 
E2 4formic acid(aq)↔CH4(aq)+3CO2(aq)+2H2O(l) 
E3 acetic acid(aq)+2O2(aq)↔2CO2(aq)+2H2O(l) 
E4 acetic acid(aq)↔CH4(aq)+CO2(aq) 
E5 propanoic acid(aq)+3.5O2(aq)↔3CO2(aq)+3H2O(l) 
E6 2lactic acid(aq)↔3acetic acid(aq) 
E7 2succinic acid(aq)+7O2(aq)↔8CO2(aq)+6H2O(l) 
E8 methanol(aq)+H2(aq)↔CH4(aq)+H2O(l) 
E9 4methanol(aq)↔3CH4(aq)+CO2(aq)+2H2O(l) 
E10 2ethanol(aq)+2CO2(aq)↔3acetic acid(aq) 
E11 2ethanol(aq)+CO2(aq)↔2acetic acid(aq)+CH4(aq) 
E12 4(2-)propanol(aq)+3CO2(aq)+2H2O(l)↔3CH4(aq)+4lactic acid(aq) 
Table 8.3

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 8.2

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
E1 −172.32 −170.74 −169.78 −167.82 −166.31 −164.23 −160.74 −156.84 −152.55 −147.91 −135.81 −115.71 
E2 −179.98 −178.10 −177.54 −176.86 −176.59 −176.42 −176.47 −176.86 −177.54 −178.48 −181.56 −187.72 
E3 −883.42 −883.07 −882.92 −882.66 −882.49 −882.27 −881.92 −881.57 −881.20 −880.81 −879.80 −878.03 
E4 −23.70 −23.79 −23.95 −24.35 −24.70 −25.21 −26.13 −27.21 −28.43 −29.78 −33.41 −39.61 
E5 −1536.84 −1536.54 −1536.37 −1536.03 −1535.78 −1535.43 −1534.83 −1534.14 −1533.37 −1532.52 −1530.19 −1525.93 
E6 −117.19 −119.16 −120.00 −121.42 −122.36 −123.52 −125.26 −126.99 −128.71 −130.44 −134.46 −140.21 
E7 −3137.41 −3138.35 −3138.85 −3139.84 −3140.57 −3141.56 −3143.18 −3144.95 −3146.84 −3148.85 −3153.85 −3161.34 
E8 −114.26 −113.66 −113.42 −113.01 −112.74 −112.40 −111.89 −111.38 −110.86 −110.32 −109.04 −107.09 
E9 −261.00 −260.12 −259.94 −259.86 −259.94 −260.15 −260.69 −261.47 −262.45 −263.60 −266.93 −273.03 
E10 −54.38 −54.85 −54.89 −54.78 −54.59 −54.23 −53.47 −52.45 −51.21 −49.75 −45.59 −38.01 
E11 −78.08 −78.64 −78.84 −79.13 −79.29 −79.45 −79.60 −79.66 −79.64 −79.53 −79.00 −77.62 
E12 132.52 132.26 132.29 132.49 132.74 133.15 133.98 135.04 136.31 137.79 141.97 149.53 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
E1 −172.32 −170.74 −169.78 −167.82 −166.31 −164.23 −160.74 −156.84 −152.55 −147.91 −135.81 −115.71 
E2 −179.98 −178.10 −177.54 −176.86 −176.59 −176.42 −176.47 −176.86 −177.54 −178.48 −181.56 −187.72 
E3 −883.42 −883.07 −882.92 −882.66 −882.49 −882.27 −881.92 −881.57 −881.20 −880.81 −879.80 −878.03 
E4 −23.70 −23.79 −23.95 −24.35 −24.70 −25.21 −26.13 −27.21 −28.43 −29.78 −33.41 −39.61 
E5 −1536.84 −1536.54 −1536.37 −1536.03 −1535.78 −1535.43 −1534.83 −1534.14 −1533.37 −1532.52 −1530.19 −1525.93 
E6 −117.19 −119.16 −120.00 −121.42 −122.36 −123.52 −125.26 −126.99 −128.71 −130.44 −134.46 −140.21 
E7 −3137.41 −3138.35 −3138.85 −3139.84 −3140.57 −3141.56 −3143.18 −3144.95 −3146.84 −3148.85 −3153.85 −3161.34 
E8 −114.26 −113.66 −113.42 −113.01 −112.74 −112.40 −111.89 −111.38 −110.86 −110.32 −109.04 −107.09 
E9 −261.00 −260.12 −259.94 −259.86 −259.94 −260.15 −260.69 −261.47 −262.45 −263.60 −266.93 −273.03 
E10 −54.38 −54.85 −54.89 −54.78 −54.59 −54.23 −53.47 −52.45 −51.21 −49.75 −45.59 −38.01 
E11 −78.08 −78.64 −78.84 −79.13 −79.29 −79.45 −79.60 −79.66 −79.64 −79.53 −79.00 −77.62 
E12 132.52 132.26 132.29 132.49 132.74 133.15 133.98 135.04 136.31 137.79 141.97 149.53 
Table 8.5

Coupled metabolic reactions involving organic carbon and inorganic nitrogen

E13 formic acid(aq)+NO3↔NO2+H2O(l)+CO2(aq) 
E14 4formic acid(aq)+NO3+H+↔NH3(aq)+4CO2(aq)+3H2
E15 acetic acid(aq)+4NO3↔2CO2(aq)+4NO2+2H2O(l) 
E16 5acetic acid(aq)+8NO3+8H+↔4N2(aq)+10CO2(aq)+14H2O(l) 
E17 acetic acid(aq)+NO3+H+↔2CO2(aq)+NH3(aq)+H2O(l) 
E18 2.5propanoic acid(aq)+7NO3+7H+↔3.5N2(aq)+7.5CO2(aq)+11H2O(l) 
E19 lactic acid(aq)+6NO3↔6NO2+3H2O(l)+3CO2(aq) 
E20 lactic acid(aq)+2NO3↔acetic acid(aq)+2NO2+CO2(aq)+H2O(l) 
E21 4lactic acid(aq)+2NO3+2H+↔4acetic acid(aq)+2NH3(aq)+4CO2(aq)+2H2O(l) 
E22 3lactic acid(aq)+2NO2+2H+↔3acetic acid(aq)+2NH3(aq)+3CO2(aq)+H2O(l) 
E23 2.5succinic acid(aq)+7NO3+7H+↔3.5N2(aq)+10CO2(aq)+11H2O(l) 
E24 benzoic acid(aq)+3.75NO3+3.75H++0.75H2O(l)↔3.75NH3(aq)+7CO2(aq) 
E25 4methanamine(aq)+2H2O(l)↔3CH4(aq)+CO2(aq)+4NH3(aq) 
E26 ethylbenzene(aq)+8.4NO3+8.4H+↔8CO2(aq)+4.2N2(aq)+9.2H2O(l) 
E13 formic acid(aq)+NO3↔NO2+H2O(l)+CO2(aq) 
E14 4formic acid(aq)+NO3+H+↔NH3(aq)+4CO2(aq)+3H2
E15 acetic acid(aq)+4NO3↔2CO2(aq)+4NO2+2H2O(l) 
E16 5acetic acid(aq)+8NO3+8H+↔4N2(aq)+10CO2(aq)+14H2O(l) 
E17 acetic acid(aq)+NO3+H+↔2CO2(aq)+NH3(aq)+H2O(l) 
E18 2.5propanoic acid(aq)+7NO3+7H+↔3.5N2(aq)+7.5CO2(aq)+11H2O(l) 
E19 lactic acid(aq)+6NO3↔6NO2+3H2O(l)+3CO2(aq) 
E20 lactic acid(aq)+2NO3↔acetic acid(aq)+2NO2+CO2(aq)+H2O(l) 
E21 4lactic acid(aq)+2NO3+2H+↔4acetic acid(aq)+2NH3(aq)+4CO2(aq)+2H2O(l) 
E22 3lactic acid(aq)+2NO2+2H+↔3acetic acid(aq)+2NH3(aq)+3CO2(aq)+H2O(l) 
E23 2.5succinic acid(aq)+7NO3+7H+↔3.5N2(aq)+10CO2(aq)+11H2O(l) 
E24 benzoic acid(aq)+3.75NO3+3.75H++0.75H2O(l)↔3.75NH3(aq)+7CO2(aq) 
E25 4methanamine(aq)+2H2O(l)↔3CH4(aq)+CO2(aq)+4NH3(aq) 
E26 ethylbenzene(aq)+8.4NO3+8.4H+↔8CO2(aq)+4.2N2(aq)+9.2H2O(l) 
Table 8.6

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 8.5

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
E13 −172.35 −172.18 −172.17 −172.22 −172.30 −172.44 −172.74 −173.12 −173.58 −174.11 −175.57 −178.11 
E14 −683.27 −682.20 −682.04 −682.14 −682.42 −683.00 −684.28 −686.00 −688.12 −690.61 −697.73 −710.66 
E15 −533.12 −534.41 −535.08 −536.37 −537.31 −538.57 −540.61 −542.83 −545.21 −547.73 −554.12 −564.32 
E16 −4231.31 −4234.99 −4237.93 −4244.50 −4249.85 −4257.54 −4270.98 −4286.53 −4304.07 −4323.50 −4375.81 −4466.95 
E17 −527.00 −527.89 −528.46 −529.63 −530.54 −531.79 −533.93 −536.35 −539.01 −541.92 −549.57 −562.55 
E18 −3679.53 −3683.53 −3686.34 −3692.38 −3697.19 −3704.00 −3715.75 −3729.20 −3744.26 −3760.83 −3805.19 −3882.00 
E19 −858.28 −861.19 −862.63 −865.26 −867.14 −869.62 −873.55 −877.74 −882.17 −886.82 −898.41 −916.58 
E20 −325.16 −326.78 −327.54 −328.90 −329.83 −331.05 −332.94 −334.91 −336.96 −339.08 −344.29 −352.26 
E21 −1288.37 −1294.10 −1296.91 −1302.09 −1305.78 −1310.63 −1318.39 −1326.67 −1335.44 −1344.70 −1368.06 −1405.51 
E22 −963.22 −967.32 −969.37 −973.20 −975.95 −979.59 −985.45 −991.75 −998.49 −1005.62 −1023.77 −1053.25 
E23 −3759.19 −3765.11 −3768.98 −3777.09 −3783.45 −3792.38 −3807.66 −3825.03 −3844.38 −3865.59 −3922.03 −4018.86 
E24 −371.58 −371.71 −371.71 −372.36 −372.45 −373.02 −373.81 −375.54 −375.72 −378.17 −385.84 −401.48 
E25 −203.07 −205.06 −206.14 −208.23 −209.75 −211.79 −215.10 −218.66 −222.45 −226.47 −236.57 −252.65 
E26 −4388.83 −4394.12 −4397.62 −4404.99 −4410.78 −4418.92 −4432.87 −4448.76 −4466.49 −4485.96 −4537.93 −4627.75 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
E13 −172.35 −172.18 −172.17 −172.22 −172.30 −172.44 −172.74 −173.12 −173.58 −174.11 −175.57 −178.11 
E14 −683.27 −682.20 −682.04 −682.14 −682.42 −683.00 −684.28 −686.00 −688.12 −690.61 −697.73 −710.66 
E15 −533.12 −534.41 −535.08 −536.37 −537.31 −538.57 −540.61 −542.83 −545.21 −547.73 −554.12 −564.32 
E16 −4231.31 −4234.99 −4237.93 −4244.50 −4249.85 −4257.54 −4270.98 −4286.53 −4304.07 −4323.50 −4375.81 −4466.95 
E17 −527.00 −527.89 −528.46 −529.63 −530.54 −531.79 −533.93 −536.35 −539.01 −541.92 −549.57 −562.55 
E18 −3679.53 −3683.53 −3686.34 −3692.38 −3697.19 −3704.00 −3715.75 −3729.20 −3744.26 −3760.83 −3805.19 −3882.00 
E19 −858.28 −861.19 −862.63 −865.26 −867.14 −869.62 −873.55 −877.74 −882.17 −886.82 −898.41 −916.58 
E20 −325.16 −326.78 −327.54 −328.90 −329.83 −331.05 −332.94 −334.91 −336.96 −339.08 −344.29 −352.26 
E21 −1288.37 −1294.10 −1296.91 −1302.09 −1305.78 −1310.63 −1318.39 −1326.67 −1335.44 −1344.70 −1368.06 −1405.51 
E22 −963.22 −967.32 −969.37 −973.20 −975.95 −979.59 −985.45 −991.75 −998.49 −1005.62 −1023.77 −1053.25 
E23 −3759.19 −3765.11 −3768.98 −3777.09 −3783.45 −3792.38 −3807.66 −3825.03 −3844.38 −3865.59 −3922.03 −4018.86 
E24 −371.58 −371.71 −371.71 −372.36 −372.45 −373.02 −373.81 −375.54 −375.72 −378.17 −385.84 −401.48 
E25 −203.07 −205.06 −206.14 −208.23 −209.75 −211.79 −215.10 −218.66 −222.45 −226.47 −236.57 −252.65 
E26 −4388.83 −4394.12 −4397.62 −4404.99 −4410.78 −4418.92 −4432.87 −4448.76 −4466.49 −4485.96 −4537.93 −4627.75 
Table 8.8

Coupled metabolic reactions involving organic carbon and inorganic sulfur

E27 CH4(aq)+SO42−+2H+↔H2S(aq)+CO2(aq)+2H2O(l) 
E28 4formic acid(aq)+SO42−+2H+↔H2S(aq)+4CO2(aq)+4H2O(l) 
E29 3formic acid(aq)+SO32−+2H+↔3CO2(aq)+H2S(aq)+3H2O(l) 
E30 4formic acid(aq)+S2O32−+2H+↔2H2S(aq)+4CO2(aq)+3H2O(l) 
E31 formic acid(aq)+S(s)↔CO2(aq)+H2S(aq) 
E32 acetic acid(aq)+2H++SO42−↔2CO2(aq)+H2S(aq)+2H2O(l) 
E33 3acetic acid(aq)+4SO32−+8H+↔6CO2(aq)+4H2S(aq)+6H2O(l) 
E34 acetic acid(aq)+S2O32−+2H+↔2H2S(aq)+2CO2(aq)+H2O(l) 
E35 acetic acid(aq)+4S(s)+2H2O(l)↔2CO2(aq)+4H2S(aq) 
E36 4propanoic acid(aq)+7SO42−+14H+↔7H2S(aq)+12CO2(aq)+12H2O(l) 
E37 4propanoic acid(aq)+3SO42−+6H+↔4acetic acid(aq)+4CO2(aq)+3H2S(aq)+4H2O(l) 
E38 3propanoic acid(aq)+7SO32−+14H+↔7H2S(aq)+9CO2(aq)+9H2O(l) 
E39 propanoic acid(aq)+SO32−+2H+↔acetic acid(aq)+H2S(aq)+CO2(aq)+H2O(l) 
E40 4propanoic acid(aq)+7S2O32−+14H+↔14H2S(aq)+12CO2(aq)+5H2O(l) 
E41 4propanoic acid(aq)+3S2O32−+6H+↔4acetic acid(aq)+6H2S(aq)+4CO2(aq)+H2O(l) 
E42 propanoic acid(aq)+7S(s)+4H2O(l)↔3CO2(aq)+7H2S(aq) 
E43 2lactic acid(aq)+3SO42−+6H+↔6CO2(aq)+3H2S(aq)+6H2O(l) 
E44 lactic acid(aq)+0.5SO42−+H+↔acetic acid(aq)+0.5H2S(aq)+CO2(aq)+H2O(l) 
E45 lactic acid(aq)+2SO32−+4H+↔3CO2(aq)+2H2S(aq)+3H2O(l) 
E46 1.5lactic acid(aq)+SO32−+2H+↔1.5acetic acid(aq)+1.5CO2(aq)+H2S(aq)+1.5H2O(l) 
E47 2lactic acid(aq)+3S2O32−+6H+↔6H2S(aq)+6CO2(aq)+3H2O(l) 
E48 2lactic acid(aq)+S2O32−+2H+↔2H2S(aq)+2acetic acid(aq)+2CO2(aq)+H2O(l) 
E49 lactic acid(aq)+6S(s)+3H2O(l)↔3CO2(aq)+6H2S(aq) 
E50 lactic acid(aq)+2S(s)+H2O(l)↔2H2S(aq)+acetic acid(aq)+CO2(aq) 
E51 2butanoic acid(aq)+5SO42−+10H+↔5H2S(aq)+8CO2(aq)+8H2
E52 butanoic acid(aq)+1.5SO42−+3H+↔acetic acid(aq)+2CO2(aq)+1.5H2S(aq)+2H2O(l) 
E53 1.5butanoic acid(aq)+5SO32−+10H+↔5H2S(aq)+6CO2(aq)+6H2
E54 butanoic acid(aq)+2SO32−+4H+↔acetic acid(aq)+2CO2(aq)+2H2S(aq)+2H2O(l) 
E55 2butanoic acid(aq)+5S2O32−+10H+↔10H2S(aq)+8CO2(aq)+3H2
E56 butanoic acid(aq)+1.5S2O32−+3H+↔acetic acid(aq)+2CO2(aq)+3H2S(aq)+0.5H2O(l) 
E57 4succinic acid(aq)+7SO42−+14H+↔16CO2(aq)+7H2S(aq)+12H2O(l) 
E58 3succinic acid(aq)+7SO32−+14H+↔7H2S(aq)+12CO2(aq)+9H2O(l) 
E59 4succinic acid(aq)+7S2O32−+14H+↔14H2S(aq)+16CO2(aq)+5H2O(l) 
E60 benzoic acid(aq)+3.75SO42−+7.5H+↔3.75H2S(aq)+7CO2(aq)+3H2O(l) 
E61 benzoic acid(aq)+5SO32−+10H+↔5H2S(aq)+7CO2(aq)+3H2O(l) 
E62 benzoic acid(aq)+3.75S2O32−+7.5H++0.75H2O(l)↔7.5H2S(aq)+7CO2(aq) 
E63 4methanol(aq)+3SO42−+6H+↔3H2S(aq)+4CO2(aq)+8H2O(l) 
E64 methanol(aq)+SO32−+2H+↔H2S(aq)+CO2(aq)+2H2O(l) 
E65 4methanol(aq)+3S2O32−+6H+↔6H2S(aq)+4CO2(aq)+5H2O(l) 
E66 methanol(aq)+3S(s)+H2O(l)↔CO2(aq)+H2S(aq) 
E67 2ethanol(aq)+3SO42−+6H+↔4CO2(aq)+3H2S(aq)+6H2O(l) 
E68 2ethanol(aq)+SO42−+2H+↔H2S(aq)+2acetic acid(aq)+2H2
E69 ethanol(aq)+2SO32−+4H+↔2CO2(aq)+2H2S(aq)+3H2O(l) 
E70 1.5ethanol(aq)+SO32−+2H+↔H2S(aq)+1.5acetic acid(aq)+1.5H2
E71 2ethanol(aq)+3S2O32−+6H+↔6H2S(aq)+4CO2(aq)+3H2O(l) 
E72 2ethanol(aq)+S2O32−+2H+↔2H2S(aq)+2acetic acid(aq)+H2
E73 ethanol(aq)+6S(s)+3H2O(l)↔2CO2(aq)+6H2S(aq) 
E74 2propanol(aq)+4.5SO42−+9H+↔6CO2(aq)+4.5H2S(aq)+8H2O(l) 
E75 4propanol(aq)+5SO42−+10H+↔4acetic acid(aq)+4CO2(aq)+5H2S(aq)+8H2O(l) 
E76 2propanol(aq)+SO42−+2H+↔2propanoic acid(aq)+H2S(aq)+2H2O(l) 
E77 propanol(aq)+3SO32−+6H+↔3H2S(aq)+3CO2(aq)+4H2O(l) 
E78 3propanol(aq)+5SO32−+10H+↔3acetic acid(aq)+5H2S(aq)+3CO2(aq)+6H2O(l) 
E79 2propanol(aq)+4.5S2O32−+9H+↔9H2S(aq)+6CO2(aq)+3.5H2O(l) 
E80 4propanol(aq)+5S2O32−+10H+↔4acetic acid(aq)+10H2S(aq)+4CO2(aq)+3H2O(l) 
E81 propanol(aq)+9S(s)+5H2O(l)↔3CO2(aq)+9H2S(aq) 
E82 butanol(aq)+3SO42−+6H+↔4CO2(aq)+3H2S(aq)+5H2O(l) 
E83 butanol(aq)+SO42−+2H+↔H2S(aq)+2acetic acid(aq)+H2
E84 butanol(aq)+4SO32−+8H+↔4CO2(aq)+4H2S(aq)+5H2O(l) 
E85 3butanol(aq)+4SO32−+8H+↔4H2S(aq)+6acetic acid(aq)+3H2
E86 butanol(aq)+3S2O32−+6H+↔4CO2(aq)+6H2S(aq)+2H2O(l) 
E87 butanol(aq)+ S2O32−+2H+↔2H2S(aq)+2acetic acid(aq) 
E88 4pentanol(aq)+15SO42−+30H+↔15H2S(aq)+20CO2(aq)+24H2
E89 pentanol(aq)+5SO32−+10H+↔5H2S(aq)+5CO2(aq)+6H2
E90 4pentanol(aq)+15S2O32−+30H+↔30H2S(aq)+20CO2(aq)+9H2
E91 octane(l)+6.25SO42−+12.5H+↔8CO2(aq)+6.25H2S(aq)+9H2O(l) 
E92 nonane(l)+7SO42−+14H+↔9CO2(aq)+7H2S(aq) 10H2O(l) 
E93 decane(l)+7.75SO42−+15.5H+↔10CO2(aq)+7.75H2S(aq)+11H2O(l) 
E94 undecane(l)+8.5SO42−+17H+↔11CO2(aq)+8.5H2S(aq)+12H2O(l) 
E95 hexadecane(l)+12.25SO42−+24.5H+↔16CO2(aq)+12.25H2S(aq)+17H2O(l) 
E96 toluene(aq)+4.5SO42−+9H+↔7CO2(aq)+4.5H2S(aq)+4H2O(l) 
E27 CH4(aq)+SO42−+2H+↔H2S(aq)+CO2(aq)+2H2O(l) 
E28 4formic acid(aq)+SO42−+2H+↔H2S(aq)+4CO2(aq)+4H2O(l) 
E29 3formic acid(aq)+SO32−+2H+↔3CO2(aq)+H2S(aq)+3H2O(l) 
E30 4formic acid(aq)+S2O32−+2H+↔2H2S(aq)+4CO2(aq)+3H2O(l) 
E31 formic acid(aq)+S(s)↔CO2(aq)+H2S(aq) 
E32 acetic acid(aq)+2H++SO42−↔2CO2(aq)+H2S(aq)+2H2O(l) 
E33 3acetic acid(aq)+4SO32−+8H+↔6CO2(aq)+4H2S(aq)+6H2O(l) 
E34 acetic acid(aq)+S2O32−+2H+↔2H2S(aq)+2CO2(aq)+H2O(l) 
E35 acetic acid(aq)+4S(s)+2H2O(l)↔2CO2(aq)+4H2S(aq) 
E36 4propanoic acid(aq)+7SO42−+14H+↔7H2S(aq)+12CO2(aq)+12H2O(l) 
E37 4propanoic acid(aq)+3SO42−+6H+↔4acetic acid(aq)+4CO2(aq)+3H2S(aq)+4H2O(l) 
E38 3propanoic acid(aq)+7SO32−+14H+↔7H2S(aq)+9CO2(aq)+9H2O(l) 
E39 propanoic acid(aq)+SO32−+2H+↔acetic acid(aq)+H2S(aq)+CO2(aq)+H2O(l) 
E40 4propanoic acid(aq)+7S2O32−+14H+↔14H2S(aq)+12CO2(aq)+5H2O(l) 
E41 4propanoic acid(aq)+3S2O32−+6H+↔4acetic acid(aq)+6H2S(aq)+4CO2(aq)+H2O(l) 
E42 propanoic acid(aq)+7S(s)+4H2O(l)↔3CO2(aq)+7H2S(aq) 
E43 2lactic acid(aq)+3SO42−+6H+↔6CO2(aq)+3H2S(aq)+6H2O(l) 
E44 lactic acid(aq)+0.5SO42−+H+↔acetic acid(aq)+0.5H2S(aq)+CO2(aq)+H2O(l) 
E45 lactic acid(aq)+2SO32−+4H+↔3CO2(aq)+2H2S(aq)+3H2O(l) 
E46 1.5lactic acid(aq)+SO32−+2H+↔1.5acetic acid(aq)+1.5CO2(aq)+H2S(aq)+1.5H2O(l) 
E47 2lactic acid(aq)+3S2O32−+6H+↔6H2S(aq)+6CO2(aq)+3H2O(l) 
E48 2lactic acid(aq)+S2O32−+2H+↔2H2S(aq)+2acetic acid(aq)+2CO2(aq)+H2O(l) 
E49 lactic acid(aq)+6S(s)+3H2O(l)↔3CO2(aq)+6H2S(aq) 
E50 lactic acid(aq)+2S(s)+H2O(l)↔2H2S(aq)+acetic acid(aq)+CO2(aq) 
E51 2butanoic acid(aq)+5SO42−+10H+↔5H2S(aq)+8CO2(aq)+8H2
E52 butanoic acid(aq)+1.5SO42−+3H+↔acetic acid(aq)+2CO2(aq)+1.5H2S(aq)+2H2O(l) 
E53 1.5butanoic acid(aq)+5SO32−+10H+↔5H2S(aq)+6CO2(aq)+6H2
E54 butanoic acid(aq)+2SO32−+4H+↔acetic acid(aq)+2CO2(aq)+2H2S(aq)+2H2O(l) 
E55 2butanoic acid(aq)+5S2O32−+10H+↔10H2S(aq)+8CO2(aq)+3H2
E56 butanoic acid(aq)+1.5S2O32−+3H+↔acetic acid(aq)+2CO2(aq)+3H2S(aq)+0.5H2O(l) 
E57 4succinic acid(aq)+7SO42−+14H+↔16CO2(aq)+7H2S(aq)+12H2O(l) 
E58 3succinic acid(aq)+7SO32−+14H+↔7H2S(aq)+12CO2(aq)+9H2O(l) 
E59 4succinic acid(aq)+7S2O32−+14H+↔14H2S(aq)+16CO2(aq)+5H2O(l) 
E60 benzoic acid(aq)+3.75SO42−+7.5H+↔3.75H2S(aq)+7CO2(aq)+3H2O(l) 
E61 benzoic acid(aq)+5SO32−+10H+↔5H2S(aq)+7CO2(aq)+3H2O(l) 
E62 benzoic acid(aq)+3.75S2O32−+7.5H++0.75H2O(l)↔7.5H2S(aq)+7CO2(aq) 
E63 4methanol(aq)+3SO42−+6H+↔3H2S(aq)+4CO2(aq)+8H2O(l) 
E64 methanol(aq)+SO32−+2H+↔H2S(aq)+CO2(aq)+2H2O(l) 
E65 4methanol(aq)+3S2O32−+6H+↔6H2S(aq)+4CO2(aq)+5H2O(l) 
E66 methanol(aq)+3S(s)+H2O(l)↔CO2(aq)+H2S(aq) 
E67 2ethanol(aq)+3SO42−+6H+↔4CO2(aq)+3H2S(aq)+6H2O(l) 
E68 2ethanol(aq)+SO42−+2H+↔H2S(aq)+2acetic acid(aq)+2H2
E69 ethanol(aq)+2SO32−+4H+↔2CO2(aq)+2H2S(aq)+3H2O(l) 
E70 1.5ethanol(aq)+SO32−+2H+↔H2S(aq)+1.5acetic acid(aq)+1.5H2
E71 2ethanol(aq)+3S2O32−+6H+↔6H2S(aq)+4CO2(aq)+3H2O(l) 
E72 2ethanol(aq)+S2O32−+2H+↔2H2S(aq)+2acetic acid(aq)+H2
E73 ethanol(aq)+6S(s)+3H2O(l)↔2CO2(aq)+6H2S(aq) 
E74 2propanol(aq)+4.5SO42−+9H+↔6CO2(aq)+4.5H2S(aq)+8H2O(l) 
E75 4propanol(aq)+5SO42−+10H+↔4acetic acid(aq)+4CO2(aq)+5H2S(aq)+8H2O(l) 
E76 2propanol(aq)+SO42−+2H+↔2propanoic acid(aq)+H2S(aq)+2H2O(l) 
E77 propanol(aq)+3SO32−+6H+↔3H2S(aq)+3CO2(aq)+4H2O(l) 
E78 3propanol(aq)+5SO32−+10H+↔3acetic acid(aq)+5H2S(aq)+3CO2(aq)+6H2O(l) 
E79 2propanol(aq)+4.5S2O32−+9H+↔9H2S(aq)+6CO2(aq)+3.5H2O(l) 
E80 4propanol(aq)+5S2O32−+10H+↔4acetic acid(aq)+10H2S(aq)+4CO2(aq)+3H2O(l) 
E81 propanol(aq)+9S(s)+5H2O(l)↔3CO2(aq)+9H2S(aq) 
E82 butanol(aq)+3SO42−+6H+↔4CO2(aq)+3H2S(aq)+5H2O(l) 
E83 butanol(aq)+SO42−+2H+↔H2S(aq)+2acetic acid(aq)+H2
E84 butanol(aq)+4SO32−+8H+↔4CO2(aq)+4H2S(aq)+5H2O(l) 
E85 3butanol(aq)+4SO32−+8H+↔4H2S(aq)+6acetic acid(aq)+3H2
E86 butanol(aq)+3S2O32−+6H+↔4CO2(aq)+6H2S(aq)+2H2O(l) 
E87 butanol(aq)+ S2O32−+2H+↔2H2S(aq)+2acetic acid(aq) 
E88 4pentanol(aq)+15SO42−+30H+↔15H2S(aq)+20CO2(aq)+24H2
E89 pentanol(aq)+5SO32−+10H+↔5H2S(aq)+5CO2(aq)+6H2
E90 4pentanol(aq)+15S2O32−+30H+↔30H2S(aq)+20CO2(aq)+9H2
E91 octane(l)+6.25SO42−+12.5H+↔8CO2(aq)+6.25H2S(aq)+9H2O(l) 
E92 nonane(l)+7SO42−+14H+↔9CO2(aq)+7H2S(aq) 10H2O(l) 
E93 decane(l)+7.75SO42−+15.5H+↔10CO2(aq)+7.75H2S(aq)+11H2O(l) 
E94 undecane(l)+8.5SO42−+17H+↔11CO2(aq)+8.5H2S(aq)+12H2O(l) 
E95 hexadecane(l)+12.25SO42−+24.5H+↔16CO2(aq)+12.25H2S(aq)+17H2O(l) 
E96 toluene(aq)+4.5SO42−+9H+↔7CO2(aq)+4.5H2S(aq)+4H2O(l) 
Table 8.9

Values of ΔGr° (kJ mol−1) at PSAT as a function of temperature for reactions given in Table 8.8

Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
E27 −103.56 −107.47 −109.35 −112.80 −115.23 −118.41 −123.46 −128.82 −134.48 −140.44 −155.45 −179.71 
E28 −283.54 −285.56 −286.89 −289.66 −291.82 −294.83 −299.93 −305.68 −312.02 −318.91 −337.02 −367.43 
E29 −289.79 −292.39 −293.89 −296.90 −299.16 −302.26 −307.42 −313.13 −319.36 −326.07 −343.53 −372.59 
E30 −296.06 −298.14 −299.50 −302.38 −304.63 −307.78 −313.12 −319.15 −325.81 −333.07 −352.17 −384.30 
E31 −40.79 −41.28 −41.59 −42.25 −42.75 −43.45 −44.63 −45.95 −47.39 −48.93 −52.79 −59.05 
E32 −127.26 −131.26 −133.30 −137.15 −139.93 −143.62 −149.59 −156.03 −162.91 −170.21 −188.86 −219.32 
E33 −690.31 −706.64 −714.82 −730.06 −740.99 −755.45 −778.65 −803.57 −830.11 −858.20 −929.64 −1045.98 
E34 −139.78 −143.83 −145.92 −149.87 −152.74 −156.57 −162.77 −169.50 −176.70 −184.38 −204.01 −236.18 
E35 −6.90 −10.82 −12.79 −16.47 −19.11 −22.59 −28.18 −34.14 −40.44 −47.02 −63.02 −88.09 
E36 −854.25 −883.47 −898.16 −925.55 −945.21 −971.20 −1012.95 −1057.76 −1105.46 −1155.94 −1284.20 −1492.70 
E37 −345.20 −358.43 −364.95 −376.96 −385.50 −396.71 −414.60 −433.65 −453.83 −475.08 −528.76 −615.42 
E38 −1180.61 −1210.10 −1224.71 −1251.74 −1271.02 −1296.42 −1337.02 −1380.43 −1426.52 −1475.18 −1598.50 −1798.57 
E39 −163.43 −167.82 −169.96 −173.90 −176.68 −180.32 −186.12 −192.29 −198.80 −205.66 −222.95 −250.86 
E40 −941.86 −971.46 −986.47 −1014.62 −1034.91 −1061.84 −1105.26 −1152.06 −1202.04 −1255.07 −1390.26 −1610.75 
E41 −382.75 −396.15 −402.80 −415.13 −423.94 −435.56 −454.16 −474.07 −495.22 −517.56 −574.21 −666.02 
E42 −2.92 −10.10 −13.65 −20.21 −24.87 −31.00 −40.76 −51.14 −62.04 −73.39 −100.83 −143.53 
E43 −498.98 −512.94 −519.91 −532.86 −542.14 −554.39 −574.02 −595.07 −617.44 −641.08 −701.04 −798.16 
E44 −122.23 −125.21 −126.65 −129.29 −131.14 −133.57 −137.42 −141.51 −145.81 −150.33 −161.66 −179.76 
E45 −403.75 −412.90 −417.41 −425.74 −431.68 −439.48 −451.96 −465.28 −479.41 −494.32 −532.05 −593.09 
E46 −260.47 −266.03 −268.70 −273.58 −277.01 −281.50 −288.61 −296.14 −304.06 −312.38 −333.26 −366.65 
E47 −536.53 −550.65 −557.76 −571.04 −580.58 −593.23 −613.58 −635.48 −658.83 −683.57 −746.49 −848.75 
E48 −256.97 −262.99 −265.92 −271.29 −275.10 −280.09 −288.03 −296.48 −305.42 −314.81 −338.47 −376.39 
E49 −68.94 −75.81 −79.19 −85.42 −89.84 −95.65 −104.89 −114.70 −125.01 −135.75 −161.77 −202.24 
E50 −62.04 −64.99 −66.40 −68.95 −70.73 −73.06 −76.72 −80.56 −84.58 −88.73 −98.74 −114.15 
E51 −607.51 −628.74 −639.34 −659.04 −673.16 −691.80 −721.69 −753.76 −787.87 −823.95 −915.58 −1064.48 
E52 −176.49 −183.11 −186.36 −192.37 −196.65 −202.28 −211.26 −220.85 −231.02 −241.76 −268.93 −312.93 
E53 −841.29 −862.62 −873.14 −892.55 −906.38 −924.58 −953.63 −984.69 −1017.63 −1052.41 −1140.50 −1283.40 
E54 −330.76 −339.54 −343.82 −351.68 −357.26 −364.57 −376.20 −388.60 −401.72 −415.53 −450.46 −506.94 
E55 −670.09 −691.59 −702.41 −722.66 −737.23 −756.54 −787.63 −821.11 −856.85 −894.76 −991.33 −1148.81 
E56 −195.27 −201.97 −205.29 −211.46 −215.87 −221.70 −231.04 −241.06 −251.72 −263.00 −291.65 −338.22 
E57 −981.70 −1014.00 −1030.38 −1061.08 −1083.23 −1112.61 −1160.00 −1211.08 −1265.65 −1323.56 −1471.14 −1711.67 
E58 −1276.20 −1308.01 −1323.88 −1353.39 −1374.54 −1402.47 −1447.31 −1495.43 −1546.66 −1600.89 −1738.71 −1962.79 
E59 −1069.32 −1102.00 −1118.69 −1150.15 −1172.93 −1203.24 −1252.31 −1305.38 −1362.23 −1422.69 −1577.20 −1829.72 
E60 −467.13 −483.38 −491.52 −506.69 −517.56 −531.94 −555.02 −579.79 −606.15 −634.05 −704.91 −820.03 
E61 −852.79 −874.45 −885.15 −904.96 −919.07 −937.67 −967.38 −999.16 −1032.88 −1068.49 −1158.73 −1305.06 
E62 −514.07 −530.51 −538.83 −554.40 −565.61 −580.49 −604.47 −630.31 −657.89 −687.16 −761.73 −883.27 
E63 −571.68 −582.52 −588.00 −598.25 −605.62 −615.38 −631.06 −647.92 −665.88 −684.90 −733.29 −812.16 
E64 −220.05 −223.84 −225.73 −229.22 −231.71 −234.99 −240.24 −245.86 −251.82 −258.12 −274.09 −300.05 
E65 −609.23 −620.23 −625.85 −636.42 −644.06 −654.22 −670.63 −688.33 −707.27 −727.39 −778.74 −862.75 
E66 −52.65 −55.30 −56.62 −59.06 −60.79 −63.07 −66.71 −70.57 −74.62 −78.83 −88.94 −104.62 
E67 −436.16 −448.63 −454.80 −466.23 −474.37 −485.10 −502.23 −520.53 −539.93 −560.40 −612.18 −695.96 
E68 −181.64 −186.10 −188.20 −191.93 −194.52 −197.86 −203.06 −208.48 −214.12 −219.97 −234.45 −257.33 
E69 −372.34 −380.74 −384.85 −392.42 −397.79 −404.84 −416.06 −428.01 −440.66 −453.98 −487.62 −542.00 
E70 −213.36 −217.79 −219.87 −223.60 −226.19 −229.54 −234.76 −240.23 −245.94 −251.86 −266.60 −290.00 
E71 −473.71 −486.34 −492.65 −504.40 −512.82 −523.94 −541.79 −560.94 −581.32 −602.89 −657.63 −746.56 
E72 −194.15 −198.68 −200.81 −204.66 −207.33 −210.80 −216.24 −221.95 −227.92 −234.13 −249.60 −274.19 
E73 −37.53 −43.66 −46.64 −52.10 −55.96 −61.01 −68.99 −77.43 −86.26 −95.40 −117.33 −151.14 
E74 −609.44 −628.69 −638.19 −655.75 −668.24 −684.68 −710.90 −738.89 −768.55 −799.81 −878.82 −1006.54 
E75 −709.83 −732.35 −743.18 −762.90 −776.78 −794.87 −823.46 −853.68 −885.46 −918.75 −1002.21 −1135.80 
E76 −182.32 −186.95 −189.12 −192.97 −195.64 −199.08 −204.43 −210.02 −215.81 −221.84 −236.73 −260.19 
E77 −536.12 −548.99 −555.28 −566.84 −575.03 −585.78 −602.87 −621.07 −640.31 −660.57 −711.70 −794.29 
E78 −918.04 −940.33 −951.02 −970.45 −984.09 −1001.88 −1029.96 −1059.63 −1090.83 −1123.50 −1205.47 −1336.88 
E79 −665.77 −685.26 −694.97 −713.00 −725.91 −742.94 −770.25 −799.51 −830.63 −863.53 −947.00 −1082.43 
E80 −772.42 −795.19 −806.26 −826.52 −840.85 −859.61 −889.40 −921.04 −954.45 −989.56 −1077.96 −1220.12 
E81 −33.90 −43.36 −47.95 −56.35 −62.28 −70.03 −82.27 −95.20 −108.71 −122.71 −156.28 −208.01 
E82 −398.27 −411.28 −417.70 −429.54 −437.96 −449.04 −466.72 −485.57 −505.55 −526.61 −579.82 −665.79 
E83 −143.75 −148.77 −151.09 −155.24 −158.11 −161.80 −167.54 −173.52 −179.74 −186.18 −202.10 −227.15 
E84 −706.80 −724.14 −732.61 −748.15 −759.17 −773.63 −796.61 −821.07 −846.93 −874.16 −942.88 −1053.82 
E85 −739.77 −759.15 −768.19 −784.35 −795.54 −809.98 −832.52 −856.07 −880.59 −906.08 −969.35 −1069.49 
E86 −435.82 −448.99 −455.55 −467.71 −476.41 −487.89 −506.28 −525.99 −546.94 −569.09 −625.27 −716.38 
E87 −156.26 −161.34 −163.71 −167.97 −170.92 −174.75 −180.73 −187.00 −193.54 −200.34 −217.25 −244.02 
E88 −1922.48 −1987.81 −2020.01 −2079.43 −2121.71 −2177.29 −2265.96 −2360.57 −2460.78 −2566.41 −2833.37 −3264.64 
E89 −866.28 −888.02 −898.64 −918.13 −931.94 −950.05 −978.86 −1009.51 −1041.92 −1076.05 −1162.16 −1301.19 
E90 −2110.23 −2176.37 −2209.25 −2270.28 −2313.92 −2371.51 −2463.77 −2562.64 −2667.74 −2778.83 −3060.63 −3517.61 
E91 −713.31 −738.55 −751.25 −774.94 −791.98 −814.53 −850.83 −889.89 −931.56 −975.74 −1088.29 −1271.94 
E92 −793.56 −822.49 −837.00 −864.06 −883.49 −909.20 −950.55 −995.01 −1042.42 −1092.66 −1220.56 −1429.06 
E93 −885.81 −917.45 −933.33 −962.96 −984.23 −1012.39 −1057.68 −1106.38 −1158.32 −1213.36 −1353.53 −1582.11 
E94 −972.08 −1006.91 −1024.38 −1056.97 −1080.37 −1111.34 −1161.14 −1214.68 −1271.77 −1332.27 −1486.32 −1737.50 
E95 −1403.39 −1454.17 −1479.61 −1527.02 −1561.04 −1606.05 −1678.38 −1756.12 −1838.97 −1926.74 −2150.12 −2514.15 
E96 −524.20 −543.26 −552.75 −570.36 −582.95 −599.55 −626.12 −654.57 −684.79 −716.71 −797.61 −928.79 
Reaction T (°C) 
 18 25 37 45 55 70 85 100 115 150 200 
E27 −103.56 −107.47 −109.35 −112.80 −115.23 −118.41 −123.46 −128.82 −134.48 −140.44 −155.45 −179.71 
E28 −283.54 −285.56 −286.89 −289.66 −291.82 −294.83 −299.93 −305.68 −312.02 −318.91 −337.02 −367.43 
E29 −289.79 −292.39 −293.89 −296.90 −299.16 −302.26 −307.42 −313.13 −319.36 −326.07 −343.53 −372.59 
E30 −296.06 −298.14 −299.50 −302.38 −304.63 −307.78 −313.12 −319.15 −325.81 −333.07 −352.17 −384.30 
E31 −40.79 −41.28 −41.59 −42.25 −42.75 −43.45 −44.63 −45.95 −47.39 −48.93 −52.79 −59.05 
E32 −127.26 −131.26 −133.30 −137.15 −139.93 −143.62 −149.59 −156.03 −162.91 −170.21 −188.86 −219.32 
E33 −690.31 −706.64 −714.82 −730.06 −740.99 −755.45 −778.65 −803.57 −830.11 −858.20 −929.64 −1045.98 
E34 −139.78 −143.83 −145.92 −149.87 −152.74 −156.57 −162.77 −169.50 −176.70 −184.38 −204.01 −236.18 
E35 −6.90 −10.82 −12.79 −16.47 −19.11 −22.59 −28.18 −34.14 −40.44 −47.02 −63.02 −88.09 
E36 −854.25 −883.47 −898.16 −925.55 −945.21 −971.20 −1012.95 −1057.76 −1105.46 −1155.94 −1284.20 −1492.70 
E37 −345.20 −358.43 −364.95 −376.96 −385.50 −396.71 −414.60 −433.65 −453.83 −475.08 −528.76 −615.42 
E38 −1180.61 −1210.10 −1224.71 −1251.74 −1271.02 −1296.42 −1337.02 −1380.43 −1426.52 −1475.18 −1598.50 −1798.57 
E39 −163.43 −167.82 −169.96 −173.90 −176.68 −180.32 −186.12 −192.29 −198.80 −205.66 −222.95 −250.86 
E40 −941.86 −971.46 −986.47 −1014.62 −1034.91 −1061.84 −1105.26 −1152.06 −1202.04 −1255.07 −1390.26 −1610.75 
E41 −382.75 −396.15 −402.80 −415.13 −423.94 −435.56 −454.16 −474.07 −495.22 −517.56 −574.21 −666.02 
E42 −2.92 −10.10 −13.65 −20.21 −24.87 −31.00 −40.76 −51.14 −62.04 −73.39 −100.83 −143.53 
E43 −498.98 −512.94 −519.91 −532.86 −542.14 −554.39 −574.02 −595.07 −617.44 −641.08 −701.04 −798.16 
E44 −122.23 −125.21 −126.65 −129.29 −131.14 −133.57 −137.42 −141.51 −145.81 −150.33 −161.66 −179.76 
E45 −403.75 −412.90 −417.41 −425.74 −431.68 −439.48 −451.96 −465.28 −479.41 −494.32 −532.05 −593.09 
E46 −260.47 −266.03 −268.70 −273.58 −277.01 −281.50 −288.61 −296.14 −304.06 −312.38 −333.26 −366.65 
E47 −536.53 −550.65 −557.76 −571.04 −580.58 −593.23 −613.58 −635.48 −658.83 −683.57 −746.49 −848.75 
E48 −256.97 −262.99 −265.92 −271.29 −275.10 −280.09 −288.03 −296.48 −305.42 −314.81 −338.47 −376.39 
E49 −68.94 −75.81 −79.19 −85.42 −89.84 −95.65 −104.89 −114.70 −125.01 −135.75 −161.77 −202.24 
E50 −62.04 −64.99 −66.40 −68.95 −70.73 −73.06 −76.72 −80.56 −84.58 −88.73 −98.74 −114.15 
E51 −607.51 −628.74 −639.34 −659.04 −673.16 −691.80 −721.69 −753.76 −787.87 −823.95 −915.58 −1064.48 
E52 −176.49 −183.11 −186.36 −192.37 −196.65 −202.28 −211