Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2009
Description:
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 (〈0.4μm 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.
Description:
Henry Houghton Fund, the
Center for BioInorganic Chemistry, the National Science Foundation (grants OCE-
0220945 and OCE-0623499), a National Defense Science and Engineering Graduate
Fellowship and the WHOI Academic Programs Office.
Keywords:
Cyanobacteria
;
Marine productivity
;
Kilo Moana (Ship) Cruise KM0701
;
Seward Johnson (Ship) Cruise SJ0609
;
Oceanus (Ship : 1975-) Cruise OC399-4
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
