Hydrogen producing activity by Escherichia coli hydrogenase 4 (hyf) depends on glucose concentration

Escherichia coli produces molecular hydrogen (H₂) during glucose fermentation. This production of H₂ occurs via multiple and reversible membrane-associated hydrogenases (Hyd). Dependence of H₂ producing rate (VH₂)$\left({\text{V}}_{{\text{H}}_2}\right)$ by Hyd-4 (hyf) on glucose concentration was studied at different pHs. During growth on 0.2% glucose at pH 7.5 in JRG3615 (hyfA-B) and JRG3621 (hyfB-R  ) mutants (VH₂)$\left({\text{V}}_{{\text{H}}_2}\right)$ was decreased ∼6.7 and ∼5 fold, respectively, compared to wild type. Only in JRG3621 mutant at pH 6.5 and 5.5 (VH₂)$\left({\text{V}}_{{\text{H}}_2}\right)$ was severely decreased ∼7.8 and ∼3.8 fold, respectively. But when cells were grown on 0.8% glucose no difference between wild type and mutants was detected at any of the tested pHs. The results indicate Hyd-4 H₂ producing activity inhibition by high concentration of glucose mainly at pH 7.5. This is of significance to regulate Hyd activity and H₂ production by E. coli during fermentation.