Effect of carbon and nitrogen sources on photo-fermentative H2 production associated with nitrogenase, uptake hydrogenase activity, and PHB accumulation in Rhodobacter sphaeroides KD131

Abstract

During photo-fermentative H2 production, the effects of carbon and nitrogen sources on nitrogenase and hydrogenase activity, poly-β-hydroxybutyrate accumulation were investigated. In succinate/ammonium sulfate medium, H2 was not detected for the first 6h because high ammonium concentration considerably reduced the nitrogenase activity to below 5nmol/g-dcw/h. After 24h, 99% of the ammonium was consumed, and the nitrogenase activity increased to 296nmol/g-dcw/h, accelerating H2 production. In contrast, the ammonium in succinate/glutamate medium was much less, which led to rapid H2 production in the beginning. However, H2 evolution was repressed over time by increased ammonium. In the presence of H2, hydrogenase activity increased with time regardless of the nitrogen source, and consequently, H2 production was reduced. Compared with succinate, H2 production in acetate media was severely limited due to increased pH over 9. During extended cultivation, the PHB accumulated in acetate media was 7 times higher than in succinate media.