A significant improvement in H-2 photoproduction was observed in the marine green alga Platymonas helgolandica var. tsingtaoensis in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). The addition of 15 mu M CCCP to algal cultures led to a 260-fold increase in H-2 production compared with a negligible volume of H-2 gas produced without CCCP. The photosystem (PS) II photochemical activity was shown to be completely inhibited in the presence of CCCP under illumination. The added herbicide 3-(3,4-dichlorophenyl)-1, 1-dimethylurea further resulted in a twofold increase in H-2 photoproduction in the CCCP-treated cultures. These results demonstrated the absence of PSII-dependent pathway of H-2 photoproduction. H-2 production essentially depends on electrons donated to the hydrogenase by the endogenous substrate catabolism in CCCP-treated P. helgolandica var. tsingtaoensis. An analysis of the O-2-tolerance of the hydrogenase of P. helgolandica var. tsingtaoensis suggested that this enzyme may belong to the class [FeFe]-hydrogenase. (C) 2011 Elsevier Ltd. All rights reserved.