Accession Number : ADA504993
Title : The Relationship Between Iron and Nitrogen Fixation in Trichodesmium spp.
Descriptive Note : Doctoral thesis
Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE
Personal Author(s) : Chappell, Phoebe D
Report Date : Jun 2009
Pagination or Media Count : 133
Abstract : 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 microns 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.
Descriptors : *PHOSPHORUS , *NITROGEN , *PACIFIC OCEAN , *NORTH ATLANTIC OCEAN , *IRON , CORRELATION , REVERSIBLE , GENES , INVERSION , TROPICAL REGIONS , ATLANTIC OCEAN , ESTERS , SEA WATER , CYANOGEN , SUBTROPICAL REGIONS , FERREDOXIN , BACTERIA , PREDICTIONS , MEASUREMENT , SARGASSO SEA , STRESSES , EQUATORIAL REGIONS
Subject Categories : Inorganic Chemistry
Physical and Dynamic Oceanography
Distribution Statement : APPROVED FOR PUBLIC RELEASE