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

Microbial Molecular hydrogen (H ₂ ) cycling plays an important role in several ecological niches. Hydrogenases (H ₂ ases), enzymes involved in H ₂ metabolism, are of great interest for investigating microbial communities, and producing BioH ₂ . To obtain an overall picture of the genetic ability of Cyanobacteria to produce H ₂ ases, we conducted a phylum wide analysis of the distribution of the genes encoding these enzymes in 130 cyanobacterial genomes. The concomitant presence of the H ₂ ase 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 H ₂ ase. The [NiFe] H ₂ ases 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 ₂ metabolism in Cyanobacteria has a broad ecological distribution, since only the genomes of strains collected from the open ocean do not possess hox genes. In addition, the presence of H ₂ ase 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 H ₂ ases belonging to groups 1, 3b, and 3d. Overall, these data show that H ₂ ases are widely distributed, and are therefore probably of great functional importance in Cyanobacteria. The present finding that homologs to oxygen-tolerant H ₂ ases are present in this phylum opens new perspectives for applying the process of photosynthesis in the field of H ₂ production.