title: Unicellular cyanobacterial distributions broaden the oceanic N2 fixation domain.
abstract: Nitrogen (N2)-fixing microorganisms (diazotrophs) are an important source of biologically available fixed N in terrestrial and aquatic ecosystems and control the productivity of oligotrophic ocean ecosystems. We found that two major groups of unicellular N2-fixing cyanobacteria (UCYN) have distinct spatial distributions that differ from those of Trichodesmium, the N2-fixing cyanobacterium previously considered to be the most important contributor to open-ocean N2 fixation. The distributions and activity of the two UCYN groups were separated as a function of depth, temperature, and water column density structure along an 8000-kilometer transect in the South Pacific Ocean. UCYN group A can be found at high abundances at substantially higher latitudes and deeper in subsurface ocean waters than Trichodesmium. These findings have implications for the geographic extent and magnitude of basin-scale oceanic N2 fixation rates.
authors.affiliation: Department of Ocean Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA. pmoisand@ucsc.edu
authors.forename: Pia H
authors.initials: PH
authors.lastname: Moisander
authors.forename: Roxanne A
authors.initials: RA
authors.lastname: Beinart
authors.forename: Ian
authors.initials: I
authors.lastname: Hewson
authors.forename: Angelicque E
authors.initials: AE
authors.lastname: White
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Johnson
authors.forename: Craig A
authors.initials: CA
authors.lastname: Carlson
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Montoya
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Zehr
mesh_terms: D018533:Biomass; D000458:Cyanobacteria / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification* / Q000378:metabolism*; D017753:Ecosystem; D005798:Genes, Bacterial; D005843:Geography; D008027:Light; D009586:Nitrogen Fixation; D010088:Oxidoreductases / Q000235:genetics; D010140:Pacific Ocean; D010839:Phytoplankton; D016133:Polymerase Chain Reaction; D012623:Seawater / Q000737:chemistry / Q000382:microbiology*; D013045:Species Specificity; D013696:Temperature
chemical_list: D010088:Oxidoreductases; C029130:nitrogenase reductase