Sharing the Secrets of Life Without Water

Extract

Water and life are inseparable. No known living thing can function without water, and there is life wherever there is water on Earth (Rothschild and Mancinelli, 2001). One of the greatest problems of living on land is thus that the air is almost always deadly dry. For example, at equilbrium with air of 50% relative humidity at 20°C, cells have a water content of about 0.1 g H₂O g⁻¹ dry mass. This is probably not enough water to surround the proteins and membranes in a cell (Billi and Potts, 2002) and so stops metabolism and kills almost all animals and plants.

However, a very few animals, a few plants, and an unknown proportion of microbes can be separated from water for a time. They can dry without dying, survive for hours to decades in a desiccated, ametabolic state, and then recover full function after rewetting. They are either small or found mainly where few other organisms can survive. Though still little-known even among biologists, this general taxonomic and ecological scope of desiccation tolerance was well-established a half-century ago (Alpert, 2000). What has awaited answer with more modern techniques are the twin puzzles raised by the prodigious survival yet modest distribution of desiccation-tolerant organisms: How do they tolerate desiccation? and Why are they not more common?