title: Possible association of diazotrophs with marine zooplankton in the Pacific Ocean.
abstract: Dinitrogen fixation, the biological reduction in N2gas to ammonia contributes to the supply of new nitrogen in the surface ocean. To understand the diversity and abundance of potentially diazotrophic (N2fixing) microorganisms associated with marine zooplankton, especially copepods, the nifH gene was studied using zooplankton samples collected in the Pacific Ocean. In total, 257 nifH sequences were recovered from 23 nifH-positive DNA extracts out of 90 copepod samples. The nifH genes derived from cyanobacteria related to Trichodesmium, α- and γ-subdivisions of proteobacteria, and anaerobic euryarchaeota related to Methanosaeta concilii were detected. Our results indicated that Pleuromamma, Pontella, and Euchaeta were the major copepod genera hosting dinitrogen fixers, though we found no species-specific association between copepods and dinitrogen fixers. Also, the digital PCR provided novel data on the number of copies of the nifH gene in individual copepods, which we report the range from 30 to 1666 copies per copepod. This study is the first systematic study of zooplankton-associated diazotrophs, covering a large area of the open ocean, which provide a clue to further study of a possible new hotspot of N2fixation.
authors.affiliation: Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Kazi Md
authors.initials: KM
authors.lastname: Azimuddin
authors.affiliation: National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama, Kanagawa, Japan.
authors.forename: Junya
authors.initials: J
authors.lastname: Hirai
authors.affiliation: Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Shotaro
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Md Nurul
authors.initials: MN
authors.lastname: Haider
authors.affiliation: Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Tachibana
authors.affiliation: Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Keigo
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Kitamura
authors.affiliation: Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Minato-Ku, Tokyo, Japan.
authors.forename: Fuminori
authors.initials: F
authors.lastname: Hashihama
authors.affiliation: Department of Aquatic Science, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-Ku, Tokyo, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Hamasaki
mesh_terms: D020561:Alphaproteobacteria / Q000201:enzymology / Q000235:genetics*; D000818:Animals; D020562:Betaproteobacteria / Q000201:enzymology / Q000235:genetics*; D033342:Copepoda / Q000382:microbiology*; D019640:Methanosarcinales / Q000201:enzymology / Q000235:genetics*; D009586:Nitrogen Fixation / Q000235:genetics*; D010088:Oxidoreductases / Q000235:genetics*; D010140:Pacific Ocean; D000072359:Trichodesmium / Q000201:enzymology / Q000235:genetics*; D015048:Zooplankton / Q000382:microbiology*
chemical_list: D010088:Oxidoreductases; C029130:nitrogenase reductase
keywords: 
  nifH
  ; Marine; Pacific Ocean; microorganisms; zooplankton