title: Distribution of a consortium between unicellular algae and the N2 fixing cyanobacterium UCYN-A in the North Atlantic Ocean.
abstract: The globally abundant, uncultured unicellular cyanobacterium UCYN-A was recently discovered living in association with a eukaryotic cell closely related to a prymnesiophyte. Here, we established a double CAtalysed Reporter Deposition-Fluorescence In Situ Hybridization (CARD-FISH) approach to identify both partners and provided quantitative information on their distribution and abundance across distinct water masses along a transect in the North Atlantic Ocean. The N2 fixation activity coincided with the detection of UCYN-A cells and was only observed in oligotrophic (< 0.067 NO3(-)  μM and < 0.04 PO4(3-)  μM) and warm (> 18°C) surface waters. Parallel 16S ribosomal RNA gene analyses among unicellular diazotrophs indicated that only UCYN-A cells were present. UCYN-A cells were associated with an algal partner or non-associated using the double CARD-FISH approach. We demonstrated that UCYN-A cells living in association with Haptophyta were the dominant form (87.0 ± 6.1%), whereas non-associated UCYN-A cells represented only a minor fraction (5.2 ± 3.9%). Interestingly, UCYN-A cells were also detected living in association with unknown single-celled eukaryotes in small amounts (7.8 ± 5.2%), presumably Alveolata. The proposed ecological niche of UCYN-A as an oligotrophic, mesophilic and obligate symbiotic nitrogen-fixing microorganism is evident for the North Atlantic Ocean.
authors.affiliation: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum GFZ Mikrobielles GeoEngineering, D-14473, Potsdam, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Krupke
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.forename: Hannah
authors.initials: H
authors.lastname: Halm
authors.forename: Bernhard M
authors.initials: BM
authors.lastname: Fuchs
authors.forename: Rudolf I
authors.initials: RI
authors.lastname: Amann
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
mesh_terms: D001267:Atlantic Ocean; D002245:Carbon Dioxide / Q000378:metabolism; D000458:Cyanobacteria / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D058087:Haptophyta / Q000235:genetics / Q000302:isolation & purification*; D017404:In Situ Hybridization, Fluorescence; D059013:Microbial Consortia; D009586:Nitrogen Fixation / Q000235:genetics; D012623:Seawater / Q000382:microbiology*
chemical_list: D002245:Carbon Dioxide