title: Two subpopulations of Crocosphaera watsonii have distinct distributions in the North and South Pacific.
abstract: Crocosphaera watsonii is a unicellular nitrogen (N2)-fixing cyanobacterium with ecological importance in oligotrophic oceans. In cultivated strains there are two phenotypes of C. watsonii (large and small cells) with differences that could differentially impact biogeochemical processes. Recent work has shown the phenotypes diverged through loss or addition of type-specific genes in a fraction of their genomes, whereas the rest of the genomes were maintained at 99-100% DNA identity. Previous molecular assays for C. watsonii abundances targeted the conserved regions and therefore could not differentiate between phenotypes, so their relative distributions in natural communities were unknown. To determine phenotype distributions, this study developed and applied type-specific quantitative polymerase chain reaction assays to samples from the North and South Pacific. Abundances of both Crocosphaera types declined sharply with depth between 45 and 75 m in both sites. In surface water small cells were 10-100 times more abundant than large cells in the N. Pacific, whereas in the S. Pacific the two phenotypes were nearly equal. Evidence for large cell aggregation was only found in N. Pacific samples. The differences in C. watsonii sub-populations in the North and South Pacific have direct implications for biogeochemistry and carbon export in oligotrophic gyres.
authors.affiliation: Department of Ocean Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA.
authors.forename: Shellie R
authors.initials: SR
authors.lastname: Bench
authors.affiliation: Department of Ocean Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA.
authors.forename: Ildiko
authors.initials: I
authors.lastname: Frank
authors.affiliation: Department of Ocean Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA.|Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA, 95039, USA.|Center for Microbial Oceanography: Research and Education, University of Hawaii, 1950 East-West Road, Honolulu, HI, 96822, USA.
authors.forename: Julie
authors.initials: J
authors.lastname: Robidart
authors.affiliation: Department of Ocean Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA.|Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA, 95039, USA.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Zehr
mesh_terms: D001483:Base Sequence; D002244:Carbon / Q000378:metabolism; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics; D016680:Genome, Bacterial / Q000235:genetics; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000235:genetics / Q000502:physiology*; D010140:Pacific Ocean; D010641:Phenotype; D016133:Polymerase Chain Reaction; D025341:Principal Component Analysis; D054712:Salinity; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D002244:Carbon; D009584:Nitrogen