Distribution of Hydrogenases in Cyanobacteria: A Phylum-Wide Genomic Survey.

Microbial Molecular hydrogen (H) cycling plays an important role in several ecological niches. Hydrogenases (Hases), enzymes involved in H metabolism, are of great interest for investigating microbial communities, and producing BioH. To obtain an overall picture of the genetic ability of Cyanobacteria to produce Hases, we conducted a phylum wide analysis of the distribution of the genes encoding these enzymes in 130 cyanobacterial genomes. The concomitant presence of the Hase and genes involved in the maturation process, and that of well-conserved catalytic sites in the enzymes were the three minimal criteria used to classify a strain as being able to produce a functional Hase. The [NiFe] Hases were found to be the only enzymes present in this phylum. Fifty-five strains were found to be potentially able produce the bidirectional Hox enzyme and 33 to produce the uptake (Hup) enzyme. H metabolism in Cyanobacteria has a broad ecological distribution, since only the genomes of strains collected from the open ocean do not possess genes. In addition, the presence of Hase was found to increase in the late branching clades of the phylogenetic tree of the species. Surprisingly, five cyanobacterial genomes were found to possess homologs of oxygen tolerant Hases belonging to groups 1, 3b, and 3d. Overall, these data show that Hases are widely distributed, and are therefore probably of great functional importance in Cyanobacteria. The present finding that homologs to oxygen-tolerant Hases are present in this phylum opens new perspectives for applying the process of photosynthesis in the field of H production.