Escherichia coli hydrogenase activity and H2 production under glycerol fermentation at a low pH

Hydrogenase (Hyd) activity and H2 production by Escherichia coli were studied at a low pH. H2 production at pH 5.5 under glycerol fermentation was shown to be ∼1.5-fold higher than that at pH 6.5 or above but less than that under glucose fermentation. It was inhibited by N,N′-dicyclohexylcarbodiimide: H2 production inhibition was increased with decreasing pH and almost maximal inhibition was observed at pH 5.5. The data on H2 production by single and double mutants with defects in different Hyd-enzymes and in fhlA gene suggest that under glycerol fermentation at a low pH, Hyd-1, Hyd-2 and Hyd-4 were operating in a reversed, non-H2 producing mode. Moreover, a role of fhlA gene in Hyd-3 and Hyd-4 activity in H2 production is proposed under glucose fermentation at a low pH.