The photosynthetic hydrogen production performance of a newly isolated Rhodobacter capsulatus JL1 with various carbon sources

Rhodobacter capsulatus is a photosynthetic bacterium with the ability to produce H2 under photosynthetic condition. In this study, a new strain JL1 isolated from lake water was identified as Rhodobacter capsulatus by phylogenetic analysis of 16S ribosomal DNA (rDNA) sequence. Initial medium pH and l-glutamate (nitrogen source) concentration were optimized. At optimum pH 7.0 and 7 mmol/L l-glutamate, R. capsulatus JL1 could grow and produce hydrogen on the carbon sources of acetate, butyrate, glucose, xylose and fructose with the maximum substrate to H2 conversion efficiencies of 67.5%, 26.6%, 46.1%, 46.2% and 46.6%, respectively. The maximum H2 production rate, 124 ± 0.6 mL/(L·h), was obtained using 20 mmol-glucose/L as the carbon source. The addition of appropriate acetic acid to the tests with low concentration of glucose was able to improve the H2 yield. Under the optimum operation parameters, the maximum H2 yield and H2 production rate of R. capsulatus JL1 from 16.4 g-corn straw/L-culture were 2966.5 ± 43.2 mL/L and 71.1 ± 4.5 mL/(L·h), while the chemical oxygen demand (COD) removal rate was up to 49.6%. This study indicates that R. capsulatus JL1 can serve as good candidate strain for H2 production with organic waste water as well as effluent of dark-fermentation.