초록
<P><B>Abstract</B></P> <P>In this study, the new strategy for long term bio-hydrogen (H<SUB>2</SUB>) production using different substrates and waste materials is presented. Growth characteristics and H<SUB>2</SUB> production were investigated upon consumption of 0.4% xylose and 1% glycerol alone (which were optimal) or their mixture by <I>Escherichia coli</I> BW25113 wild type parental strain (PS) and Δ<I>hyaB</I>, Δ<I>hybC</I>, Δ<I>hycE</I>, Δ<I>hyfG</I> mutants with genes deletions for key subunits of hydrogenase (Hyd)-1 to Hyd-4, respectively, in high and low buffer capacity peptone (HPM, LPM) mediums, pH 5.5 and 7.5. Overall, pH 5.5 negatively affected bacterial growth and H<SUB>2</SUB> production. At pH 7.5, apart from Hyd-3 and Hyd-4 mutants, upon growth of PS, Hyd-1 and Hyd-2 mutants drop of Pt redox electrode readings from positive (∼+150 mV) to negative (of −400 to −550 mV) values was detected during log growth phase mentioning H<SUB>2</SUB> formation. Xylose and glycerol co-utilization did not affect PS and Hyd-1 and Hyd-2 mutant's biomass and H<SUB>2</SUB> formation during log growth phase in LPM, but ∼1.5 fold stimulated these parameters, especially in HPM, pH 7.5, during prolonged 96 h bacterial growth. Roles of Hyd-3 and Hyd-4 in H<SUB>2</SUB> production; and Hyd-1 and Hyd-2 in H<SUB>2</SUB> oxidation during bacterial log growth phase were stated under xylose and glycerol co-fermenting conditions. The results obtained might be valuable for industrial long term H<SUB>2</SUB> production by bacteria using mixture of carbon sources and combining various organic waste materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Biomass formation and H<SUB>2</SUB> production by <I>E. coli</I> were determined during prolonged (96 h) growth. </LI> <LI> Xylose and glycerol co-supplementation stimulated 1.5-fold biomass formation. </LI> <LI> They also enhanced 1.5-fold H<SUB>2</SUB> production. </LI> <LI> Growth medium high buffering capacity and pH 7.5 positively affected H<SUB>2</SUB> production. </LI> <LI> Hydrogenase (Hyd)-3 and Hyd-4 are essential for pH homeostasis and H<SUB>2</SUB> production. </LI> </UL> </P>