Enhanced biohydrogen production by an ammonium-tolerant Rhodobacter capsulatus from sugarcane bagasse

Lignocellulosic biomass is an abundant and renewable resource from plants, and has great potential as an alternative to fossil resources to produce second-generation biofuels. Biohydrogen production from lignocellulosic biomass is an attractive approach to generate clean energy. Here a new ammonium-tolerant mutant named Rhodobacter capsulatus WH02 was isolated by transposon mutagenesis. Batch experiments were conducted to investigate the effects of key parameters such as inoculum concentration (5%–60%, v/v), glucose concentration (10–50 mmol/L), and ammonium concentration (2–8 mmol/L) on photo-fermentation of WH02. The results showed that the hydrogen yield of WH02 was about 3.74 folds of the wild type strain at 8 mmol/L ammonium chloride addition, suggesting the mutant strain WH02 exhibited improved biohydrogen production performance under ammonium suppression conditions compared with the wild type strain. Sugarcane bagasse (SCB) hydrolysate with high ammonium concentration (87.94 ± 2.22 mmol/L) was used as substrate to evaluate the ammonium-tolerant performance of WH02. The maximum hydrogen production was up to 153.96 ± 1.98 mL-H₂/g-SCB by WH02 from SCB hydrolysate with the energy conversion efficiency of hydrogen of 10.95%, demonstrating the feasibility of producing biohydrogen from lignocellulosic wastes containing high ammonium by the ammonium-tolerant strain WH02.