title: Distribution analysis of hydrogenases in surface waters of marine and freshwater environments.
abstract: BACKGROUND
  Surface waters of aquatic environments have been shown to both evolve and consume hydrogen and the ocean is estimated to be the principal natural source. In some marine habitats, H(2) evolution and uptake are clearly due to biological activity, while contributions of abiotic sources must be considered in others. Until now the only known biological process involved in H(2) metabolism in marine environments is nitrogen fixation.
  
  
  RESULTS
  We analyzed marine and freshwater environments for the presence and distribution of genes of all known hydrogenases, the enzymes involved in biological hydrogen turnover. The total genomes and the available marine metagenome datasets were searched for hydrogenase sequences. Furthermore, we isolated DNA from samples from the North Atlantic, Mediterranean Sea, North Sea, Baltic Sea, and two fresh water lakes and amplified and sequenced part of the gene encoding the bidirectional NAD(P)-linked hydrogenase. In 21% of all marine heterotrophic bacterial genomes from surface waters, one or several hydrogenase genes were found, with the membrane-bound H(2) uptake hydrogenase being the most widespread. A clear bias of hydrogenases to environments with terrestrial influence was found. This is exemplified by the cyanobacterial bidirectional NAD(P)-linked hydrogenase that was found in freshwater and coastal areas but not in the open ocean.
  
  
  CONCLUSIONS
  This study shows that hydrogenases are surprisingly abundant in marine environments. Due to its ecological distribution the primary function of the bidirectional NAD(P)-linked hydrogenase seems to be fermentative hydrogen evolution. Moreover, our data suggests that marine surface waters could be an interesting source of oxygen-resistant uptake hydrogenases. The respective genes occur in coastal as well as open ocean habitats and we presume that they are used as additional energy scavenging devices in otherwise nutrient limited environments. The membrane-bound H(2)-evolving hydrogenases might be useful as marker for bacteria living inside of marine snow particles.
authors.affiliation: Botanisches Institut, Christian-Albrechts-Universität, Kiel, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Barz
authors.forename: Christian
authors.initials: C
authors.lastname: Beimgraben
authors.forename: Torsten
authors.initials: T
authors.lastname: Staller
authors.forename: Frauke
authors.initials: F
authors.lastname: Germer
authors.forename: Friederike
authors.initials: F
authors.lastname: Opitz
authors.forename: Claudia
authors.initials: C
authors.lastname: Marquardt
authors.forename: Christoph
authors.initials: C
authors.lastname: Schwarz
authors.forename: Kirstin
authors.initials: K
authors.lastname: Gutekunst
authors.forename: Klaus Heinrich
authors.initials: KH
authors.lastname: Vanselow
authors.forename: Ruth
authors.initials: R
authors.lastname: Schmitz
authors.forename: Julie
authors.initials: J
authors.lastname: LaRoche
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Schulz
authors.forename: Jens
authors.initials: J
authors.lastname: Appel
mesh_terms: D001267:Atlantic Ocean; D001419:Bacteria / Q000145:classification / Q000201:enzymology / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D000458:Cyanobacteria / Q000145:classification / Q000201:enzymology / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D017753:Ecosystem; D005618:Fresh Water / Q000382:microbiology*; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism*; D008522:Mediterranean Sea; D054892:Metagenome / Q000235:genetics; D008969:Molecular Sequence Data; D009659:North Sea; D010802:Phylogeny; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D006859:Hydrogen; D006864:Hydrogenase