Nitrogen fixation and nitrogenase (nifH) expression in tropical waters of the eastern North Atlantic

• Published in: The ISME Journal
• Main Authors: Turk, Kendra A., Rees, Andrew P., Zehr, Jonathan P., Pereira, Nicole, Swift, Paul, Shelley, Rachel, Lohan, Maeve, Woodward, E. Malcolm S, Gilbert, Jack
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: North Atlantic; North East Atlantic
• Online Access: https://eprints.soton.ac.uk/414023/

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 nmolNl -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.