H-2 activation by the oxygen-tolerant hydrogenase from the purple sulfur bacterium Thiacapsa roseopersicina, using electron mediators of cyanobacterial and algal origin, has been demonstrated. Ferredoxins, either from the cyanobacterium Synechococcus PCC7942 or the green alga Scenedesmus obliquus, are capable of providing electrons for hydrogenase-mediated Hz evolution. The high-potential cytochrome c(6) from Synechococcus PCC7942 proved to be capable of accepting electrons derived from hydrogenase-mediated Hz oxidation. In subsequent experiments, Thiocapsa hydrogenase was introduced into the cells of Synechococcus PCC7942 by electroporation, for enhanced H-2 production.