Hydrogen production by Escherichia coli depends on glucose concentration and its combination with glycerol at different pHs

•H2 production rate (VH2)(VH2) by Escherichia coli during fermentation was shown to depend on glucose or glycerol.•VH2VH2 is inhibited with glucose concentration (form 0.05% to 0.2%) at pH 7.5 and 6.5 but not pH 5.5.•VH2VH2 during glycerol fermentation is increased upon shift in its concentration (from 0.5 to 1%) at pH 5.5.•VH2VH2 is stimulated by glycerol added into the medium with 0.1% glucose at pH 6.5.•VH2VH2 during mixed carbon fermentation is changed upon glucose or glycerol assays at different pHs.

Escherichia coli produces molecular hydrogen (H2) during glucose or mixed carbon (glucose and glycerol) fermentation. Dependence of H2 production rate (VH2)(VH2) on glucose at different pHs was studied in a concentration dependent manner. During growth of wild-type on glucose, increasing glucose concentration from 0.05% to 0.2% resulted in the marked inhibition of VH2VH2. Inhibitory effect of glucose was shown at pH 7.5 and 6.5 but not pH 5.5. However, glycerol added in the growth medium with 0.1% glucose significantly increased VH2VH2 but different effects at different pHs were established upon glucose or glycerol assays. The results indicate that H2 production is inhibited by glucose in a concentration dependent manner during glucose fermentation but glucose in combination with glycerol might enhance H2 production during mixed carbon fermentation.