Chapter 13: H2 Producing Activity by Escherichia Coli During Mixed Carbon Fermentation at Slightly Alkaline and Acidic pHs: Novel Functions of Hydrogenase 4 (hyf) and Hydrogenase 2 (hyb)

Abstract

Molecular hydrogen (H2) production by Escherichia coli was studied during mixed carbon (glucose and glycerol) fermentation at slightly alkaline (7.5) and acidic (5.5) pHs. Wild type cells, in the assays with glucose, produced H2 at pH 7.5 with the same level as cells grown on glucose. Compared to wild type, H2 production in fhlA and fhlA hyfG mutants decreased ~6.5 and ~7.9 fold, respectively. In wild type cells H2 formation at pH 5.5 was lowered ~2 fold, compared to the cells grown on glucose. But in hyfG and hybC mutants H2 production was decreased ~2 and ~1.6 fold, respectively. However, at pH 7.5, in the assays with glycerol, H2 production was low, when compared to the cells grown on glycerol. In contrast to slightly alkaline pH, at pH 5.5 in the assays with glycerol H2 production was absent. Moreover, H2 evolution in wild type cells was inhibited by 0.3 mM N,N′-dicyclohexylcarbodiimide (DCCD), an inhibitor of the F0F1-ATPase, in a pH dependent manner. At pH 7.5 in wild type cells H2 production was decreased ~3 fold but at pH 5.5 the inhibition was ~1.7 fold. At both pHs in fhlA mutant H2 formation was totally inhibited by DCCD. Taken together, the results indicate that at pH 7.5 in the presence of glucose glycerol also can be fermented. They suggest that Hyd-4 mainly and Hyd-2 to some extent contribute in H2 production by E. coli during mixed carbon fermentation at pH 5.5 whereas Hyd-1 is only responsible for H2 oxidation. © Springer Science+Business Media Dordrecht 2013.