Abstract
Cyanobacteria have two types of hydrogenase, uptake hydrogenase (Hup) and bidirectional hydrogenase (Hox). We studied distribution of hydrogenase genes and activities among 15 nitrogen-fixing cyanobacteria and found that all of them have hup. Twelve of them also have hox, but 3 of them lack it. Although Nostoc PCC7422 has a hox gene cluster, Hox activity of the cell extracts was found to be very low. We have cloned and sequenced the complete hox gene cluster from the cosmid library. The hox genes in Nostoc PCC7422 are organized as hoxEFUY-ORF-hoxH with only one intervening ORF. While in other strains several ORFs interrupt the hox genes. The strain has hoxE, the observation being the second to the report of Anabaena PCC7120 among 4 nitrogen-fixing cyanobacteria for which hox gene clusters have been sequenced. We have also sequenced hupSL that show high homologies with those of other cyanobacteria.
