title: Nitrogen fixation and nitrogenase (nifH) expression in tropical waters of the eastern North Atlantic.
abstract: Expression of nifH in 28 surface water samples collected during fall 2007 from six stations in the vicinity of the Cape Verde Islands (north-east Atlantic) was examined using reverse transcription-polymerase chain reaction (RT-PCR)-based clone libraries and quantitative RT-PCR (RT-qPCR) analysis of seven diazotrophic phylotypes. Biological nitrogen fixation (BNF) rates and nutrient concentrations were determined for these stations, which were selected based on a range in surface chlorophyll concentrations to target a gradient of primary productivity. BNF rates greater than 6 nmolN l(-1) h(-1) were measured at two of the near-shore stations where high concentrations of Fe and PO(4)(3-) were also measured. Six hundred and five nifH transcripts were amplified by RT-PCR, of which 76% are described by six operational taxonomic units, including Trichodesmium and the uncultivated UCYN-A, and four non-cyanobacterial diazotrophs that clustered with uncultivated Proteobacteria. Although all five cyanobacterial phylotypes quantified in RT-qPCR assays were detected at different stations in this study, UCYN-A contributed most significantly to the pool of nifH transcripts in both coastal and oligotrophic waters. A comparison of results from RT-PCR clone libraries and RT-qPCR indicated that a γ-proteobacterial phylotype was preferentially amplified in clone libraries, which underscores the need to use caution interpreting clone-library-based nifH studies, especially when considering the importance of uncultivated proteobacterial diazotrophs.
authors.affiliation: Department of Ocean Sciences, University of California Santa Cruz, Santa Cruz, CA, USA. kturk@ucsc.edu
authors.forename: Kendra A
authors.initials: KA
authors.lastname: Turk
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Rees
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Zehr
authors.forename: Nicole
authors.initials: N
authors.lastname: Pereira
authors.forename: Paul
authors.initials: P
authors.lastname: Swift
authors.forename: Rachel
authors.initials: R
authors.lastname: Shelley
authors.forename: Maeve
authors.initials: M
authors.lastname: Lohan
authors.forename: E Malcolm S
authors.initials: EM
authors.lastname: Woodward
authors.forename: Jack
authors.initials: J
authors.lastname: Gilbert
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D055726:Cabo Verde; D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics; D015723:Gene Library; D007501:Iron / Q000032:analysis; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000235:genetics*; D010802:Phylogeny; D020560:Proteobacteria / Q000201:enzymology* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012623:Seawater / Q000032:analysis / Q000382:microbiology*; D014871:Water Microbiology
chemical_list: D001426:Bacterial Proteins; D002734:Chlorophyll; D007501:Iron; D009591:Nitrogenase; D000077194:Chlorophyll A