In vitro functional characterization of the Na⁺/H⁺ antiporters in Corynebacterium glutamicum

Corynebacterium glutamicum, typically used as industrial workhorse for amino acid production, is a moderately salt–alkali-tolerant microorganism with optimal growth at pH 7–9. However, little is known about the mechanisms of salt–alkali tolerance in C. glutamicum. Here, the catalytic capacity of three putative Na⁺/H⁺ antiporters from C. glutamicum (designated as Cg-Mrp1, Cg-Mrp2 and Cg-NhaP) were characterized in an antiporter-deficient Escherichia coli KNabc strain. Only Cg-Mrp1 was able to effectively complement the Na⁺-sensitive of E. coli KNabc. Cg-Mrp1 exhibited obvious Na⁺(Li⁺)/H⁺ antiport activities with low apparent Km values of 1.08 mM and 1.41 mM for Na⁺ and Li⁺, respectively. The Na⁺/H⁺ antiport activity of Cg-Mrp1 was optimal in the alkaline pH range. All three antiporters showed detectable K⁺/H⁺ antiport activitiy. Cg-NhaP also exhibited Na⁺(Li⁺,Rb⁺)/H⁺ antiport activities but at lower levels of activity. Interestingly, overexpression of Cg-Mrp2 exhibited clear Na⁺(K⁺)/H⁺ antiport activities. These results suggest that C. glutamicum Na⁺(K⁺)/H⁺ antiporters may have overlapping roles in coping with salt–alkali and perhaps high-osmolarity stress.

Corynebactrerium glutamicum, Na⁺/H⁺ antiporters, function