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

Abstract

Microbial Molecular hydrogen (H2) cycling plays an important role in several ecological niches. Hydrogenases (H2ases), enzymes involved in H2 metabolism, are of great interest for investigating microbial communities, and producing BioH2. To obtain an overall picture of the genetic ability of Cyanobacteria to produce H2ases, we conducted a phylum wide analysis of the distribution of the genes encoding these enzymes in 130 cyanobacterial genomes. The concomitant presence of the H2ase 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 H2ase. The [NiFe] H2ases 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. H2 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 H2ase 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 H2ases belonging to groups 1, 3b, and 3d. Overall, these data show that H2ases are widely distributed, and are therefore probably of great functional importance in Cyanobacteria. The present finding that homologs to oxygen-tolerant H2ases are present in this phylum opens new perspectives for applying the process of photosynthesis in the field of H2 production.

Molecular Hydrogen, a Neglected Key Driver of Soil Biogeochemical Processes

“…Group 3d [NiFe]-hydrogenases consist of a heteromeric hydrogenase and a NADH-dehydrogenase module that binds to NAD(P)H (20). The amount of hydrogenase subunits varies greatly, consisting of, for example, a heterodimeric enzyme in C. necator (56) or a heteropentameric enzyme in Cyanobacteria (57). These hydrogenases are used to balance the NAD ϩ /NADH pool by reducing NAD ϩ using H 2 (20).…”

Overproduction of the cyanobacterial hydrogenase and selection of a mutant thriving on urea, as a possible step towards the future production of hydrogen coupled with water treatment

“…The annual solar flux received by Earth is in vast excess of the total energy used by human societies, and the burning of hydrogen liberates a high amount of energy (142 MJ/kg for H 2 vs. 44.2 MJ/kg for oil) while producing only water (H 2 O) as a by-product. As a consequence, there is a growing interest in cyanobacteria, the photosynthetic microorganisms that can use solar energy, water, CO 2 , mineral and salts for the production of H 2 , while saving arable soils, fertilizers and fresh waters for agriculture (for recent reviews see [ 1 – 3 ]). Furthermore, several model cyanobacteria have a small sequenced genome easily manipulable, such as the presently studied unicellular strain Synechocystis PCC6803 (hereafter designated as Synechocystis ).…”

Overproduction of the Flv3B flavodiiron, enhances the photobiological hydrogen production by the nitrogen-fixing cyanobacterium Nostoc PCC 7120

“…The second type of enzymes producing H 2 are hydrogenases (H 2 ases). Bidirectional NiFe H 2 ases (called Hox), which catalyze both H 2 oxidation and proton reduction, are largely distributed across the cyanobacterial phylum [2,3]. They form a heteropentamer with a H 2 ase part (HoxYH) and a diaphorase part (HoxEFU).…”