title: Discovery of symbiotic nitrogen fixation and chemoautotrophy in cold-water corals.
abstract: Cold-water corals (CWC) are widely distributed around the world forming extensive reefs at par with tropical coral reefs. They are hotspots of biodiversity and organic matter processing in the world's deep oceans. Living in the dark they lack photosynthetic symbionts and are therefore considered to depend entirely on the limited flux of organic resources from the surface ocean. While symbiotic relations in tropical corals are known to be key to their survival in oligotrophic conditions, the full metabolic capacity of CWC has yet to be revealed. Here we report isotope tracer evidence for efficient nitrogen recycling, including nitrogen assimilation, regeneration, nitrification and denitrification. Moreover, we also discovered chemoautotrophy and nitrogen fixation in CWC and transfer of fixed nitrogen and inorganic carbon into bulk coral tissue and tissue compounds (fatty acids and amino acids). This unrecognized yet versatile metabolic machinery of CWC conserves precious limiting resources and provides access to new nitrogen and organic carbon resources that may be essential for CWC to survive in the resource-depleted dark ocean.
authors.affiliation: Department of Earth Sciences, Utrecht University, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands.
authors.forename: Jack J
authors.initials: JJ
authors.lastname: Middelburg
authors.affiliation: Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research (NIOZ-Yerseke), P.O. Box 140, 4400 AC Yerseke, The Netherlands.
authors.forename: Christina E
authors.initials: CE
authors.lastname: Mueller
authors.affiliation: Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research (NIOZ-Yerseke), P.O. Box 140, 4400 AC Yerseke, The Netherlands.
authors.forename: Bart
authors.initials: B
authors.lastname: Veuger
authors.affiliation: Dept. of Marine Sciences, Tjärnö, University of Gothenburg, 452 96 Strömstad, Sweden.
authors.forename: Ann I
authors.initials: AI
authors.lastname: Larsson
authors.affiliation: GEOMAR, Helmholtz Centre for Ocean Research, Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Armin
authors.initials: A
authors.lastname: Form
authors.affiliation: Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research (NIOZ-Yerseke), P.O. Box 140, 4400 AC Yerseke, The Netherlands.
authors.forename: Dick
authors.initials: D
authors.lastname: van Oevelen
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D064751:Ammonium Compounds / Q000378:metabolism; D000818:Animals; D037421:Anthozoa / Q000254:growth & development* / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism; D052837:Chemoautotrophic Growth; D003080:Cold Temperature; D005227:Fatty Acids / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D014867:Water
chemical_list: D000596:Amino Acids; D064751:Ammonium Compounds; D005227:Fatty Acids; D014867:Water; D002244:Carbon; D009584:Nitrogen