In vitro functional characterization of the na+/h+ antiporters in corynebacterium glutamicum

Abstract

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 1.08mM and 1.41mM 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.