Abstract
Glycerol fermentation redox routes by E. coli wild type batch cultures and effects of Ni2+, Fe2+ and Fe3+ ions of different concentration (0.01–0.3 mM) on cell growth and H2 production were investigated. Influences of aforementioned metal ions and Cu2+, as well as Fe2+ on H2 production rate in vitro assays were also studied in wild type and hyaB hybC double mutant (with defective hydrogenase (Hyd) 1 and Hyd -2). Cell growth was shown to be followed by decrease of pH and redox potential (ORP) measured by both titanium-silicate (Eh) and platinum electrodes (E′h). After 8 h growth, at pH 7.5, Eh dropped down negative value (−120 mV) and H2 production was observed at the middle log phase. Whereas at the same pH in the presence of 0.05 mM Fe2+ both Eh and Eh′ electrodes readings dropped to more negative values ~ −170 ± 10 and −450 ± 12 mV, respectively. All ions used at 0.05–0.1 mM concentrations stimulated bacterial growth ~1.2 to ~1.4 fold at different pHs. Ni2+ enhanced H2 formation in a concentration-dependent manner: maximal stimulation, up to 1.5 fold, was observed at 0.2 mM NiCl2 only at pH 7.5. Ni2+ also promoted to high H2 yield at pH 6.5 and 7.5 in vitro. In addition, 0.05–0.1 mM Fe2+ also affected on H2 production rate and increased it ~2 fold in vitro at pH 6.5 and 7.5 whereas, 0.05–0.1 mM Cu2+ had inhibitory effect on H2 production rate. In hyaB hybC mutant H2 production rate was decreased compared with wild type and Fe2+ had no effect on H2 production rate and yield both at pH 6.5 and 7.5.
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