title: Distinct ecological niches of marine symbiotic N2-fixing cyanobacterium Candidatus Atelocyanobacterium thalassa sublineages.
abstract: A recently described symbiosis between the metabolically streamlined nitrogen-fixing cyanobacterium UCYN-A and a single-celled eukaryote prymnesiophyte alga is widely distributed throughout tropical and subtropical marine waters, and is thought to contribute significantly to nitrogen fixation in these regions. Several UCYN-A sublineages have been defined based on UCYN-A nitrogenase (nifH) sequences. Due to the low abundances of UCYN-A in the global oceans, currently existing molecular techniques are limited for detecting and quantifying these organisms. A targeted approach is needed to adequately characterize the diversity of this important marine cyanobacterium, and to advance understanding of its ecological importance. We present findings on the distribution of UCYN-A sublineages based on high throughput sequencing of UCYN-A nifH PCR amplicons from 78 samples distributed throughout many major oceanic provinces. These UCYN-A nifH fragments were used to define oligotypes, alternative taxonomic units defined by nucleotide positions with high variability. The data set was dominated by a single oligotype associated with the UCYN-A1 sublineage, consistent with previous observations of relatively high abundances in tropical and subtropical regions. However, this analysis also revealed for the first time the widespread distribution of the UCYN-A3 sublineage in oligotrophic waters. Furthermore, distinct assemblages of UCYN-A oligotypes were found in oligotrophic and coastally influenced waters. This unique data set provides a framework for determining the environmental controls on UCYN-A distributions and the ecological importance of the different sublineages.
authors.affiliation: Ocean Sciences Department, University of California, Santa Cruz, California, 95064, USA.
authors.forename: Kendra A
authors.initials: KA
authors.lastname: Turk-Kubo
authors.affiliation: Ocean Sciences Department, University of California, Santa Cruz, California, 95064, USA.|Centre for Ecology and Evolution in Microbial Model Systems (EEMiS), Linnaeus University, 392 34, Kalmar, Sweden.
authors.forename: Hanna M
authors.initials: HM
authors.lastname: Farnelid
authors.affiliation: Ocean Sciences Department, University of California, Santa Cruz, California, 95064, USA.
authors.forename: Irina N
authors.initials: IN
authors.lastname: Shilova
authors.affiliation: Ocean Sciences Department, University of California, Santa Cruz, California, 95064, USA.
authors.forename: Britt
authors.initials: B
authors.lastname: Henke
authors.affiliation: Ocean Sciences Department, University of California, Santa Cruz, California, 95064, USA.
authors.forename: Jonathan P
authors.identifier: 0000-0002-5691-5408
authors.initials: JP
authors.lastname: Zehr
mesh_terms: D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D004463:Ecology; D009586:Nitrogen Fixation / Q000502:physiology; D009591:Nitrogenase / Q000378:metabolism; D016133:Polymerase Chain Reaction; D013559:Symbiosis / Q000502:physiology
chemical_list: D009591:Nitrogenase
keywords: Candidatus Atelocyanobacterium thalassa; UCYN-A; nifH; nitrogen fixation; nitrogenase; oligotyping