During fermentation Escherichia coli produces di-hydrogen (H ) via reversible membrane-bound [Ni-Fe]-hydrogenases (Hyd). This study describes the total and N,N'-dicyclohexylcarbodiimide (DCCD) inhibited ATPase activity and H production at various pHs in E. coli wild type and mutants encoding Hyd enzymes and formate dehydrogenases (FDH) on fermentation of glucose, glycerol, and formate. The highest total ATPase activity was detected at pH 7.5 in hyaB hybC selC (lacking large subunits of Hyd-1 and Hyd-2 and FDH, respectively) triple mutant. This ATPase activity was mainly due to the proton-translocating ATPase but in FDH mutant the DCCD inhibition was less compared to wild type. Potassium ions stimulated total ATPase activity at pH 5.5 ~50% and ~35% in wild type and hypF (lacking all Hyd enzymes) mutant, respectively. Moreover, K also stimulated DCCD inhibited ATPase activity ~1.7-fold-2-fold in strains where FDH was absent only at pH 5.5. DCCD inhibited H production only at pH 5.5 in all assays. Taken together it is suggested that at low pH, FDH, and Hyd enzymes are linked with the F F -ATPase for regulating and maintaining the cytoplasmatic pH and thus proton motive force generation. FDH and Hyd enzymes have impact on the F F -ATPase activity depending on external pH and potassium ions. © 2018 IUBMB Life, 70(10):1040-1047, 2018.

In this study anaerobic utilization of mixed carbon sources (glucose, glycerol, formate) and generation of fermentation end-products by Escherichia coli at slightly alkaline and slightly acidic pHs was investigated at the first time. It has been shown that E. coli is able to perform co-fermentation of glucose and glycerol in the presence of external formate. The latter was utilized by bacterial cells at first. Acetate is the permanent product (25–50 mM) during both glucose and glycerol utilization. It has been revealed that composition of fermentation end-products depends not only on external pH, but also on co-utilization of substrates.

Escherichia coli is able to ferment not only single but also mixtures of carbon sources. The formate metabolism and effect of formate on various enzymes have been extensively studied during sole glucose but not mixed carbon sources utilization. It was revealed that in membrane vesicles (MV) of wild type cells grown at pH 7.5 during fermentation of the mixture of glucose (2 g/L), glycerol (10 g/L), and formate (0.68 g/L), in the assays, the addition of formate (10 mM) increased the N,N′‐dicyclohexylcarbodiimide (DCCD)‐inhibited ATPase activity on ~30% but no effect of potassium ions (100 mM) had been detected. In selC (coding formate dehydrogenases) and fdhF (coding formate dehydrogenase H) single mutants, formate increased DCCD‐inhibited ATPase activity on ~40 and ~70%, respectively. At pH 5.5, in wild type cells MV, formate decreased the DCCD‐inhibited ATPase activity ~60% but unexpectedly in the presence of potassium ions, it was stimulated ~5.8 fold. The accessible SH or thiol groups number in fdhF mutant was less by 28% compared with wild type. In formate assays, the available SH groups number was less ~10% in wild type but not in fdhF mutant. Taken together, the data suggest that proton ATPase activity depends on externally added formate in the presence of potassium ions at low pH. This effect might be regulated by the changes in the number of redox‐active thiol groups via formate dehydrogenase H, which might be directly related to proton ATPase FO subunit.

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This research is focused on the investigation of specific growth rate changes of $E.~coli$ wild type and mutant strains with defect of Hyd, FDH enzymes and FhlA regulatory protein in the presence of $N,N'$-dicyclohexylcarbodiimide (DCCD) and external formate various concentration during co-fermentation of glucose, glycerol and formate at pHs $5.5-7.5.$ The highest value of SGR was observed at pH 7.5. It was revealed that SGR depends on external formate concentration at all pHs. DCCD inhibitory effect was shown mainly at pH 7.5 and partially at pH 6.5 and 5.5. In the case of the F0F1-ATPase inhibition FhlA compensatory effect on SGR was revealed.