Relation of potassium uptake to proton transport and activity of hydrogenases in Escherichia coli grown at low pH

Abstract

Escherichia coli grown under anaerobic conditions in acidic medium (pH 5.5) upon hyperosmotic stress accumulates potassium ions mainly through the Kup system, the functioning of which is associated with proton efflux decrease. It was shown that H + secretion but not glucose-induced K + uptake was inhibited by N,N'-dicyclohexylcarbodiimide (DCC). The inhibitory effect of DCC on the H + efflux was stronger in the trkA mutant with defective potassium transport. The K + and H + fluxes depended on the extent of hyperosmotic stress in the absence or presence of DCC. The decrease in external oxidation/reduction potential and H 2 liberation insen- sitive to DCC were recorded. It was found that the atpD mutant with nonfunctional F 0 F 1 -ATPase produced a sub- stantial amount of H 2 , while in the hyc mutant (but not the hyf mutant defective in hydrogenases 3 (Hyd-3) and 4 (Hyd-4)) the H 2 production was significantly suppressed. At the same time, the rate of K + uptake was mark- edly lower in hyfR and hyfB-R but not in hycE or hyfA-B mutants; H + transport was lowered and sensitive to DCC in hyf but not in hyc mutants. The results point to the relationship of K + uptake with the Hyd-4 activity. Novel options of the expression of some hyf genes in E. coli grown at pH 5.5 are proposed. It is possible that the hyfB-R genes expressed under acidic conditions or their gene products interact with the gene coding for the Kup protein or directly with the Kup system.