The relationship between iron and nitrogen fixation in Trichodesmium spp.

• Main Author: Chappell, Phoebe Dreux
• Other Authors: James W. Moffett, John B. Waterbury and Eric A. Webb., Woods Hole Oceanographic Institution., Joint Program in Oceanography/Applied Ocean Science and Engineering, Woods Hole Oceanographic Institution, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology 2009
• Subjects: /Woods Hole Oceanographic Institution. Joint Program in Oceanography/Applied Ocean Science and Engineering; Earth; Atmospheric; and Planetary Sciences; Woods Hole Oceanographic Institution; Cyanobacteria; Marine productivity; Pacific; Phoebe; North Atlantic
• Online Access: http://hdl.handle.net/1721.1/53103

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. Includes bibliographical references. Trichodesmium spp. are considered the dominant nitrogen (N) fixing cyanobacteria in tropical and subtropical oceans, regimes frequently characterized by low iron (Fe). Limited information exists about what levels of Fe limit Trichodesmium N fixation. I developed a diagnostic for Fe limitation using quantitative reverse transcription PCR (qRT-PCR) of the Fe stress response gene isiB, which encodes for flavodoxin a non-Fe containing substitute for ferredoxin. I determined that high isiB gene expression corresponded to cell-specific reductions in N fixation rates in both phylogenetic clades of Trichodesmium grown on varying levels of Fe. Using these laboratory-determined thresholds, I assessed Fe limitation of Trichodesmium from the Sargasso Sea, equatorial Atlantic Ocean and Western Pacific Warm Pool in conjunction with other analytical measurements (N, phosphorus (P) and dissolved Fe (<0.4[mu]m filtered)). I found widespread Fe limitation in Trichodesmium from the Pacific Ocean and minimal expression in the North Atlantic Ocean. I also found an inverse correlation between isiB expression and dissolved Fe:P ratios in seawater and data suggesting that most dissolved Fe in seawater, including organic ligand-bound Fe, is available to Trichodesmium. These data support and refine previous model predictions and demonstrate, in situ, the importance of Fe to the marine N cycle. by Phoebe Dreux Chappell. S.M.