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.