Diversity in hydrogen evolution from bidirectional hydrogenases in cyanobacteria from terrestrial, freshwater and marine intertidal environments

We characterized a set of 36 strains of cyanobacteria isolated from terrestrial, freshwater and marine intertidal settings to probe their potential to produce hydrogen from excess reductant, in the hope of finding novel strains with improved traits for biohydrogen production. The set was diverse with respect to origin, morphology, taxonomy and phylogeny. We found that about one half of the strains could produce hydrogen from hydrogenases in standard assays, a trait that corresponded invariably with the presence of homologues of the gene hoxH, coding for subunit H in the bidirectional Ni-Fe hydrogenase. Strains from freshwater and intertidal settings had a high incidence of hydrogen producing, hoxH containing strains, but all terrestrial isolates were negative for both. While specific rates of hydrogen production varied among strains, some novel strains displayed rates several fold higher than those previously reported. We detected two different patterns in hydrogen production. Pattern 1, corresponding to that previously known in Synechocystis PCC 6803, encompassed strains whose hydrogenase system produced hydrogen only temporarily to revert to hydrogen consumption within a short time and after reaching moderate hydrogen concentrations. Cyanobacteria displaying pattern 2, in the genera Lyngbya and Microcoleus, tended to have higher rates, did not reverse the direction of the reaction and reached much higher concentrations of hydrogen at steady state, making them of interest as potential platforms for biohydrogen production.