Hydrogen production by Escherichia coli using brewery waste: Optimal pretreatment of waste and role of different hydrogenases

Brewery spent grains (BSG), one of the by-products of brewery production, were used for Escherichia coli growth and hydrogen (H2) production. The dilute acid and alkali pretreatment methods were used to hydrolyze the rough lignocellulose structure, and optimal conditions for the BSG hydrolysate (BSGH) preparation were developed. E. coli BW25113 wild type strain and hydrogenase (Hyd)-negative mutants with deletions of genes encoding key subunits of Hyd 1-4 (ΔhyaB, ΔhybC, ΔhycE, ΔhyfG), as well as for a ΔhyaB ΔhybC double mutant were investigated with regards to growth, acidification of the medium, redox potential kinetics and H2 production when using BSGH. Readings of redox Pt electrode dropped to −400 ± 10 mV, with H2 yield of ∼0.75 mmol H2 L−1 at the 3rd h wild type strain growth. Changes in redox Ti-Si electrode readings were negligible. H2 production was not observed with defective Hyd-3 and Hyd-4; therefore, Hyd-3 and Hyd-4 are responsible for H2 production using BSGH, whereas defective Hyd-1 and Hyd-2 led to a ∼2-fold stimulation of H2 yield. The data were confirmed by determining cumulative H2 yield. These findings are useful for development of renewable energy, especially H2 production biotechnology, using different organic wastes as sustainable energy feedstocks.