title: Facets of diazotrophy in the oxygen minimum zone waters off Peru.
abstract: Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4(+)), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2 fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance of nifH, the functional gene marker for N2 fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2 fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2(-) and PO4(3-) are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the future.
authors.affiliation: Institute of General Microbiology, Christian Albrechts University Kiel, Kiel, Germany.
authors.forename: Carolin R
authors.initials: CR
authors.lastname: Loescher
authors.affiliation: 1] Helmholtz Center for Ocean Research Kiel (GEOMAR), Kiel, Germany [2] School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry, UK.
authors.forename: Tobias
authors.initials: T
authors.lastname: Großkopf
authors.affiliation: 1] Helmholtz Center for Ocean Research Kiel (GEOMAR), Kiel, Germany [2] Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Falguni D
authors.initials: FD
authors.lastname: Desai
authors.affiliation: Helmholtz Center for Ocean Research Kiel (GEOMAR), Kiel, Germany.
authors.forename: Diana
authors.initials: D
authors.lastname: Gill
authors.affiliation: 1] Institute of General Microbiology, Christian Albrechts University Kiel, Kiel, Germany [2] Helmholtz Center for Ocean Research Kiel (GEOMAR), Kiel, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Schunck
authors.affiliation: Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway (NUI Galway), Ireland.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Croot
authors.affiliation: National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, Southampton, UK.
authors.forename: Christian
authors.initials: C
authors.lastname: Schlosser
authors.affiliation: Institute of General Microbiology, Christian Albrechts University Kiel, Kiel, Germany.
authors.forename: Sven C
authors.initials: SC
authors.lastname: Neulinger
authors.affiliation: Institute of General Microbiology, Christian Albrechts University Kiel, Kiel, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Pinnow
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
authors.affiliation: 1] Helmholtz Center for Ocean Research Kiel (GEOMAR), Kiel, Germany [2] Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: LaRoche
authors.affiliation: Institute of General Microbiology, Christian Albrechts University Kiel, Kiel, Germany.
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Schmitz
mesh_terms: D001105:Archaea / Q000235:genetics / Q000302:isolation & purification; D001419:Bacteria / Q000235:genetics / Q000302:isolation & purification; D000458:Cyanobacteria / Q000235:genetics / Q000302:isolation & purification; D058440:Denitrification; D052836:Heterotrophic Processes; D009566:Nitrates / Q000032:analysis; D009586:Nitrogen Fixation / Q000235:genetics; D009792:Oceans and Seas; D010088:Oxidoreductases / Q000145:classification / Q000235:genetics; D010100:Oxygen / Q000032:analysis; D010568:Peru; D010802:Phylogeny; D020560:Proteobacteria / Q000235:genetics / Q000302:isolation & purification; D012623:Seawater / Q000737:chemistry / Q000382:microbiology*
chemical_list: D009566:Nitrates; D010088:Oxidoreductases; C029130:nitrogenase reductase; D010100:Oxygen