Escherichia coli wild type and hydrogenase mutant cells growth and hydrogen production upon xylose and glycerol co-fermentation in media with different buffer capacities

Abstract

In this study, the new strategy for long term bio-hydrogen (H2) production using different substrates and waste materials is presented. Growth characteristics and H2 production were investigated upon consumption of 0.4% xylose and 1% glycerol alone (which were optimal) or their mixture by Escherichia coli BW25113 wild type parental strain (PS) and ΔhyaB, ΔhybC, ΔhycE, ΔhyfG mutants with genes deletions for key subunits of hydrogenase (Hyd)-1 to Hyd-4, respectively, in high and low buffer capacity peptone (HPM, LPM) mediums, pH 5.5 and 7.5. Overall, pH 5.5 negatively affected bacterial growth and H2 production. At pH 7.5, apart from Hyd-3 and Hyd-4 mutants, upon growth of PS, Hyd-1 and Hyd-2 mutants drop of Pt redox electrode readings from positive (∼+150 mV) to negative (of −400 to −550 mV) values was detected during log growth phase mentioning H2 formation. Xylose and glycerol co-utilization did not affect PS and Hyd-1 and Hyd-2 mutant's biomass and H2 formation during log growth phase in LPM, but ∼1.5 fold stimulated these parameters, especially in HPM, pH 7.5, during prolonged 96 h bacterial growth. Roles of Hyd-3 and Hyd-4 in H2 production; and Hyd-1 and Hyd-2 in H2 oxidation during bacterial log growth phase were stated under xylose and glycerol co-fermenting conditions. The results obtained might be valuable for industrial long term H2 production by bacteria using mixture of carbon sources and combining various organic waste materials.