Diversity of cyanobacterial hydrogenases, a molecular approach

In an effort to elucidate the diversity of cyanobacterial hydrogenases, we used a molecular approach. Filamentous strains from a broad range of source s were screened for the presence of hup (uptake hydrogenase), xisC (rearran gement within hupL), and hox (bidirectional hydrogenase) genes. As expected , an uptake hydrogenase seems to be present in all N-2-fixing cyanobacteria . On the other hand, no evidence was found for the presence of a convention al bidirectional enzyme in several strains. Similarly, the presence of xisC is not a characteristic shared by all the heterocyst-forming cyanobacteria . Although tempting, it is not possible to establish a correlation between the presence/absence of the bidirectional hydrogenase and the occurrence of xisC. Thr natural molecular variation of hydrogenases in cyanobacteria is certainly a field to explore, both to understand the physiological function s of the respective enzymes and to identify a genetic background to be used when constructing a strain for photobiological H-2 production in a bioreac tor.