title: Nitrogen fixation in a chemoautotrophic lucinid symbiosis.
abstract: The shallow water bivalve Codakia orbicularis lives in symbiotic association with a sulfur-oxidizing bacterium in its gills. The endosymbiont fixes CO2and thus generates organic carbon compounds, which support the host's growth. To investigate the uncultured symbiont's metabolism and symbiont-host interactions in detail we conducted a proteogenomic analysis of purified bacteria. Unexpectedly, our results reveal a hitherto completely unrecognized feature of the C. orbicularis symbiont's physiology: the symbiont's genome encodes all proteins necessary for biological nitrogen fixation (diazotrophy). Expression of the respective genes under standard ambient conditions was confirmed by proteomics. Nitrogenase activity in the symbiont was also verified by enzyme activity assays. Phylogenetic analysis of the bacterial nitrogenase reductase NifH revealed the symbiont's close relationship to free-living nitrogen-fixing Proteobacteria from the seagrass sediment. The C. orbicularis symbiont, here tentatively named 'Candidatus Thiodiazotropha endolucinida', may thus not only sustain the bivalve's carbon demands. C. orbicularis may also benefit from a steady supply of fixed nitrogen from its symbiont-a scenario that is unprecedented in comparable chemoautotrophic symbioses.
authors: Department of Pharmaceutical Biotechnology, E.M.A. University of Greifswald, Institute of Pharmacy, Greifswald, Germany.|Département de Biologie, Institut de Biologie Paris-Seine, UMR 7138 - Evolution Paris-Seine, Equipe Biologie de la Mangrove, Université des Antilles, UFR des Sciences Exactes et Naturelles, BP 592, 97159 Pointe-à-Pitre cedex, Guadeloupe, France.
authors: Sten
authors: S
authors: König
authors: Département de Biologie, Institut de Biologie Paris-Seine, UMR 7138 - Evolution Paris-Seine, Equipe Biologie de la Mangrove, Université des Antilles, UFR des Sciences Exactes et Naturelles, BP 592, 97159 Pointe-à-Pitre cedex, Guadeloupe, France.
authors: Olivier
authors: O
authors: Gros
authors: Department of Pharmaceutical Biotechnology, E.M.A. University of Greifswald, Institute of Pharmacy, Greifswald, Germany.
authors: Stefan E
authors: SE
authors: Heiden
authors: Department of Pharmaceutical Biotechnology, E.M.A. University of Greifswald, Institute of Pharmacy, Greifswald, Germany.|Institute of Marine Biotechnology, Greifswald, Germany.
authors: Tjorven
authors: T
authors: Hinzke
authors: Göttingen Genomics Laboratory, Göttingen, Germany.
authors: Andrea
authors: A
authors: Thürmer
authors: Göttingen Genomics Laboratory, Göttingen, Germany.
authors: Anja
authors: http://orcid.org/0000-0002-2473-6202
authors: A
authors: Poehlein
authors: E.M.A. University of Greifswald, Institute of Microbiology, Greifswald, Germany.
authors: Susann
authors: S
authors: Meyer
authors: Département de Biologie, Institut de Biologie Paris-Seine, UMR 7138 - Evolution Paris-Seine, Equipe Biologie de la Mangrove, Université des Antilles, UFR des Sciences Exactes et Naturelles, BP 592, 97159 Pointe-à-Pitre cedex, Guadeloupe, France.
authors: Magalie
authors: M
authors: Vatin
authors: CIRAD - UMR QUALISUD, Station de Neufchateau, 97130 Capesterre Belle-Eau, Guadeloupe, France.
authors: Didier
authors: D
authors: Mbéguié-A-Mbéguié
authors: Département de Biologie, Institut de Biologie Paris-Seine, UMR 7138 - Evolution Paris-Seine, Equipe Biologie de la Mangrove, Université des Antilles, UFR des Sciences Exactes et Naturelles, BP 592, 97159 Pointe-à-Pitre cedex, Guadeloupe, France.
authors: Jennifer
authors: J
authors: Tocny
authors: Department of Pharmaceutical Biotechnology, E.M.A. University of Greifswald, Institute of Pharmacy, Greifswald, Germany.
authors: Ruby
authors: R
authors: Ponnudurai
authors: Göttingen Genomics Laboratory, Göttingen, Germany.
authors: Rolf
authors: http://orcid.org/0000-0002-8646-7925
authors: R
authors: Daniel
authors: E.M.A. University of Greifswald, Institute of Microbiology, Greifswald, Germany.
authors: Dörte
authors: D
authors: Becher
authors: Department of Pharmaceutical Biotechnology, E.M.A. University of Greifswald, Institute of Pharmacy, Greifswald, Germany.|Institute of Marine Biotechnology, Greifswald, Germany.
authors: Thomas
authors: T
authors: Schweder
authors: Department of Pharmaceutical Biotechnology, E.M.A. University of Greifswald, Institute of Pharmacy, Greifswald, Germany.|Institute of Marine Biotechnology, Greifswald, Germany.
authors: Stephanie
authors: S
authors: Markert
mesh_terms: D000818:Animals; D049872:Bivalvia / Q000382:microbiology*; D052837:Chemoautotrophic Growth; D020563:Gammaproteobacteria / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005880:Gills / Q000382:microbiology; D053858:Metabolic Networks and Pathways / Q000235:genetics; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics; D010802:Phylogeny; D020543:Proteome / Q000032:analysis; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D020543:Proteome; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase