Participation of hydrogenase 4, encoded by hyf Operon, in liberation of molecular hydrogen and proton-potassium exchange by Escherichia Coli

An interplay between production of H₂ and H⁺-K⁺-exchange with stable stoichiometry of N,N′-dicyclohexylcarbodiimide (DCC)-inhibited ion fluxes that is equal to 2H⁺/K⁺ under different external pH and K⁺ activity has been established for fermenting Escherichia coli grown under anaerobic conditions at pH 7.5 (Trchounian et al. / Biol. Membrany. 1999. V. 16. P. 416-428 (Russian)). In the present study, the production of H₂ was observed in fermenting bacteria grown at pH 7.5 or 6.5 and inhibited by DCC. H₂ production was absent when bacteria were grown at pH 7.5 in the medium containing formate or upon hypo-osmotic stress. It had no sensitivity to osmotic stress when bacteria were grown at pH 6.5. Formation of H₂ and 2H⁺/K⁺-exchange were not observed in mutants with deletions of hyf operon genes, encoding membrane-associated hydrogenase 4. Unlike parental strain, valinomycin had no effect on K⁺ influx by these mutants. When bacteria were grown at pH 6.5 and upon hyper-osmotic stress, these mutants produced H₂ and carried out 2H⁺/K⁺-exchange. Participation of hydrogenase 4 in the production of H₂ and proton-potassium exchange by fermenting E. coli grown at pH 7.5 is suggested. It is possible that the other hydrogenase - hydrogenase 3, is responsible for the production of H₂, when bacteria were grown at pH 6.5 or in the medium containing formate.