Characterization of Hydrogen Production by Escherichia coli Wild-type and Mutants of Hydrogenases Utilizing Xylose as Fermentation Substrate

Abstract

Xylose, one of the most common sugars derived from lignocellulosic material, can be fermented by bacteria. Escherichia coli uses natural sugars to produce biomass and H2. The latter can be formed from the formate via formate hydrolysis (FHL) during the fermentation of xylose or glucose; [Ni-Fe]-hydrogenase (Hyd) is involved in H2 formation. The growth, H2 production characteristics of E. coli BW25113 (wild-type), and ΔhyaB, ΔhybC, ΔhycE, or ΔhyfG mutant strains with deletions of catalytic subunits of Hyd-1 to Hyd-4, respectively, were monitored with addition of 0, 0.5, to 1% xylose on peptone and minimal salt-based mediums, pH 5.5 and pH 7.5. At pH 5.5, with the growth of bacteria on both media, H2 produced in the early logarithmic phase (1.40–0.02 mmol H2 L−1), whereas at pH 7.5 it is noticeably delayed. Results showed that during the fermentation of xylose, Hyd-3 and Hyd-4 are important for both bacterial growth and production of H2, mainly at pH 5.5. In addition, high xylose concentrations can stimulate the activity of the Hyd-1 enzyme during bacterial growth at pH 7.5. These results are new and important for developing advanced H2 production technologies using xylose as a feedstock.