초록
<P><B>Abstract</B></P> <P>Changes in oxidation–reduction potential (ORP) values during <I>Escherichia coli</I> Δ<I>hyaB</I> Δ<I>hybC</I> 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. H<SUB>2</SUB> 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 (K<SUB>3</SUB>[Fe(CN)<SUB>6</SUB>]), whereas at pH 7.5 the reagents had no significant effects. H<SUB>2</SUB> production was stimulated by ∼1.4 fold with mutant compared to the wild type at pH 7.5. Moreover, 3 mM DTT stimulated H<SUB>2</SUB> 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 K<SUB>3</SUB>[Fe(CN)<SUB>6</SUB>] completely inhibited H<SUB>2</SUB> 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 7.5H<SUB>2</SUB> formation by the wild type was inhibited by ∼1.2 fold, while in the case of mutant H<SUB>2</SUB> 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 H<SUB>2</SUB> production by <I>E. coli</I> and indicate the importance of reductive conditions for enhanced H<SUB>2</SUB> production as well.</P> <P><B>Highlights</B></P> <P> <UL> <LI> H<SUB>2</SUB> production was enhanced in <I>Escherichia coli</I> hydrogense 1 and 2 lacked mutant at pH 7.5. </LI> <LI> Reducing agent <SMALL>DL</SMALL>-dithiothreitol (DTT) stimulated H<SUB>2</SUB> production at both pHs 5.5 and 7.5. </LI> <LI> Oxidant potassium ferricyanide completely inhibited H<SUB>2</SUB> formation in <I>E coli</I> mutant and wild type. </LI> <LI> The findings indicate the importance of reductive conditions for H<SUB>2</SUB> production by <I>E. coli</I>. </LI> </UL> </P>