title: Diazotroph Diversity in the Sea Ice, Melt Ponds, and Surface Waters of the Eurasian Basin of the Central Arctic Ocean.
abstract: The Eurasian basin of the Central Arctic Ocean is nitrogen limited, but little is known about the presence and role of nitrogen-fixing bacteria. Recent studies have indicated the occurrence of diazotrophs in Arctic coastal waters potentially of riverine origin. Here, we investigated the presence of diazotrophs in ice and surface waters of the Central Arctic Ocean in the summer of 2012. We identified diverse communities of putative diazotrophs through targeted analysis of thenifHgene, which encodes the iron protein of the nitrogenase enzyme. We amplified 529nifHsequences from 26 samples of Arctic melt ponds, sea ice and surface waters. These sequences resolved into 43 clusters at 92% amino acid sequence identity, most of which were non-cyanobacterial phylotypes from sea ice and water samples. One cyanobacterial phylotype related toNodulariasp. was retrieved from sea ice, suggesting that this important functional group is rare in the Central Arctic Ocean. The diazotrophic community in sea-ice environments appear distinct from other cold-adapted diazotrophic communities, such as those present in the coastal Canadian Arctic, the Arctic tundra and glacial Antarctic lakes. Molecular fingerprinting ofnifHand the intergenic spacer region of the rRNA operon revealed differences between the communities from river-influenced Laptev Sea waters and those from ice-related environments pointing toward a marine origin for sea-ice diazotrophs. Our results provide the first record of diazotrophs in the Central Arctic and suggest that microbial nitrogen fixation may occur north of 77°N. To assess the significance of nitrogen fixation for the nitrogen budget of the Arctic Ocean and to identify the active nitrogen fixers, further biogeochemical and molecular biological studies are needed.
authors.affiliation: HGF-MPG Group for Deep Sea Ecology and Technology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine ResearchBremerhaven, Germany; HGF-MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine MicrobiologyBremen, Germany.
authors.forename: Mar
authors.initials: M
authors.lastname: Fernández-Méndez
authors.affiliation: Department of Ocean Sciences, University of California at Santa Cruz, Santa Cruz CA, USA.
authors.forename: Kendra A
authors.initials: KA
authors.lastname: Turk-Kubo
authors.affiliation: HGF-MPG Group for Deep Sea Ecology and Technology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research Bremerhaven, Germany.
authors.forename: Pier L
authors.initials: PL
authors.lastname: Buttigieg
authors.affiliation: HGF-MPG Group for Deep Sea Ecology and Technology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine ResearchBremerhaven, Germany; HGF-MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine MicrobiologyBremen, Germany.
authors.forename: Josephine Z
authors.initials: JZ
authors.lastname: Rapp
authors.affiliation: Sea Ice Physics Section, Climate Sciences Department, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research Bremerhaven, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Krumpen
authors.affiliation: Department of Ocean Sciences, University of California at Santa Cruz, Santa Cruz CA, USA.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Zehr
authors.affiliation: HGF-MPG Group for Deep Sea Ecology and Technology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine ResearchBremerhaven, Germany; HGF-MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine MicrobiologyBremen, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Boetius
keywords: Arctic; bacterial diversity; nifH; nitrogen fixation; non-cyanobacterial diazotrophs; sea ice