초록
Molecular hydrogen (H<SUB>2</SUB>) production by Escherichia coli was studied during mixed carbon sources (glucose and glycerol) fermentation at pH 7.5 and pH 5.5. H<SUB>2</SUB> production rate (V<SUB>H2</SUB>) by bacterial cells grown on mixed carbon was assayed with either adding glucose (glucose assay) or glycerol (glycerol assay) and compared with the cells grown on sole carbon (glucose or glycerol only) and appropriately assayed. Wild type cells grown on mixed carbon, in the assays with adding glucose, produced H<SUB>2</SUB> at pH 7.5 with the same level as in the cells grown on glucose only. At pH 7.5 V<SUB>H2</SUB> in fhlA single and fhlA hyfG double mutants decreased ~6.5 and ~7.9 fold, respectively. In wild type cells grown on mixed carbon V<SUB>H2</SUB> at pH 5.5 was lowered ~2 fold, compared to the cells grown on glucose only. But in hyfG and hybC single mutants V<SUB>H2</SUB> was decreased ~2 and ~1.6 fold, respectively. However, at pH 7.5, in the assays with glycerol, V<SUB>H2</SUB> was low, when compared to the cells grown on glycerol only. At pH 5.5 in the assays with glycerol V<SUB>H2</SUB> was absent. Moreover, V<SUB>H2</SUB> in wild type cells was inhibited by 0.3 mM N,N<SUP>'</SUP>-dicyclohexylcarbodiimide (DCCD), an inhibitor of the F<SUB>0</SUB>F<SUB>1</SUB>-ATPase, in a pH dependent manner. At pH 7.5 in wild type cells V<SUB>H2</SUB> was decreased ~3 fold but at pH 5.5 the inhibition was ~1.7 fold. At both pHs in fhlA mutant V<SUB>H2</SUB> was totally inhibited by DCCD. Taken together, the results obtained indicate that at pH 7.5, in the presence of glucose, glycerol can also be fermented. They point out that Hyd-4 mainly and Hyd-2 to some extent contribute in H<SUB>2</SUB> production by E. coli during mixed carbon fermentation at pH 5.5 whereas Hyd-1 is only responsible for H<SUB>2</SUB> oxidation.