The shallow water bivalve Codakia orbicularis lives in symbiotic association with a sulfur-oxidizing bacterium in its gills. The endosymbiont fixes CO2 and 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.
Nitrogen fixation in a chemoautotrophic lucinid symbiosis
Sten König,O. Gros,Stefan E. Heiden,Tjorven Hinzke,A. Thürmer,Anja Poehlein,Susann Meyer,Magalie Vatin,Didier Mbeguie-A-Mbeguie,Jennifer Tocny,R. Ponnudurai,R. Daniel,D. Becher,T. Schweder,Stephanie Markert
Published 2016 in Nature Microbiology
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- Publication year
2016
- Venue
Nature Microbiology
- Publication date
2016-10-24
- Fields of study
Biology, Medicine, Environmental Science
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Semantic Scholar, PubMed
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