During photo-fermentative H-2 production, the effects of carbon and nitrogen sources on nitrogenase and hydrogenase activity, poly-beta-hydroxybutyrate accumulation were investigated. In succinate/ammonium sulfate medium, H-2 was not detected for the first 6 h because high ammonium concentration considerably reduced the nitrogenase activity to below 5 nmol/g-dcw/h. After 24 h, 99% of the ammonium was consumed, and the nitrogenase activity increased to 296 nmol/g-dcw/h, accelerating H-2 production. In contrast, the ammonium in succinate/glutamate medium was much less, which led to rapid H-2 production in the beginning. However. H-2 evolution was repressed over time by increased ammonium. In the presence of H-2, hydrogenase activity increased with time regardless of the nitrogen source, and consequently, H-2 production was reduced. Compared with succinate, H-2 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. (C) 2012 Elsevier Ltd. All rights reserved.