Hydrogen production by Escherichia coli during glucose fermentation: Effects of oxidative and reductive routes used by the strain lacking hydrogen oxidizing hydrogenases 1 (hya) and 2 (hyb)

Abstract

Changes in oxidation–reduction potential (ORP) values during Escherichia coli ΔhyaB ΔhybC double mutant lacking of large subunits of hydrogenases 1 (Hyd-1) and 2 (Hyd-2) and effects of redox reagents were studied upon glucose fermentation at acidic (5.5) and alkaline (7.5) pHs. H2 production yield was determined by the readings of platinum and titanium-silicate electrodes. Specific growth rate of mutant was inhibited by ∼1.3 fold at pH 5.5 in the presence of membrane-permeating reducing agent DL-dithiothreitol (DTT) and impermeable oxidant potassium ferricyanide (K3[Fe(CN)6]), whereas at pH 7.5 the reagents had no significant effects. H2 production was stimulated by ∼1.4 fold with mutant compared to the wild type at pH 7.5. Moreover, 3 mM DTT stimulated H2 production yield by ∼2 and ∼4 fold during bacterial log growth phase at pH 5.5 and pH 7.5, respectively. While at pH 5.5 1 mM K3[Fe(CN)6] completely inhibited H2 formation by mutant as well as wild type resulting in alternation of ORP to positive values (200 ± 10 mV) at the end of log growth phase. At pH 7.5H2 formation by the wild type was inhibited by ∼1.2 fold, while in the case of mutant H2 formation was completely inhibited, but resulting in decrease of ORP to negative values (−270 ± 12 mV) at the end of log growth phase. These findings point out the effects of lacked Hyd-1 and Hyd-2 both on H2 production by E. coli and indicate the importance of reductive conditions for enhanced H2 production as well.