Mechanisms of enhanced bio-H₂ production in Ethanoligenens harbinense by L-cysteine supplementation: Analyses at growth and gene transcription levels

Bio-H₂, produced from lignocellulosic biomass or organic wastewater, is an ideal future energy candidate due to its feature of renewability and sustainability. In order to uncover the mechanisms of the reducing agent of L-cysteine in bio-H₂ production process, effects of L-cysteine on oxidation–reduction potential (ORP), cell growth, H₂ yield by Ethanoligenens harbinense were investigated. Meanwhile, effects of L-cysteine on the expression of genes such as [FeFe]-hydrogenase (hydA), acetate kinase (AK), alcohol dehydrogenase (ADH), and lactate dehydrogenase (LDH) were analysed by quantitative reverse transcription PCR (qRT-PCR). The maximum H₂ yield of 1.88 mol-H₂/mol-glucose and dry cell weight of 0.92 g/L, which were about 1.57 and 1.51 folds of that of negative control, were obtained with supplementation of 800 mg/L L-cysteine. The experimental results indicated that the supplementation of L-cysteine at a suitable dosage (<800 mg/L) can enhances the H₂ production by E. harbinense. The underlying mechanisms include decreasing ORP, promoting cell growth, and stimulating expression of key functional genes (hydA, AK, and ADH) involved in H₂ production, together promoted the H₂ release and enhanced the H₂ production rate.