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 September 2009
Description:
Trichodesmium is a colonial, N2-fixing cyanobacterium found in tropical
oceans. Species of Trichodesmium are genetically similar but several species exist together
in the same waters. In order to coexist, Trichodesmium spp. may occupy different
niche spaces through differential utilization of resources such as nutrients and light,
and through responses to physical characteristics such as temperature and turbulence. To
investigate niche differentiation in Trichodesmium, I characterized cultured strains of Trichodesmium,
identified and enumerated Trichodesmium clades in the field, and investigated
P stress and N2 fixation in field populations. Species of Trichodesmium grouped
into two clades based on sequences from 16S rDNA, the internal transcribed spacer (ITS),
and the heterocyst differentiation gene hetR. Clade I contained Trichodesmium erythraeum
and Trichodesmium contortum, and clade II contained Trichodesmium thiebautii, Trichodesmium
tenue, Trichodesmium hildebrandtii, and Trichodesmium pelagicum. Each
clade was morphologically diverse, but species within each clade had similar pigmentation.
I developed a quantitative polymerase chain reaction (qPCR) method to distinguish
between these two clades. In field populations of the Atlantic and Pacific Oceans,
the qPCR method revealed that clade II Trichodesmium spp. were more prominent than
clade I in the open ocean. Concentrations of Trichodesmium did not correlate with nutrient
concentrations, but clade I had wider temperature and depth distributions than clade
II. Temperature and light are physical characteristics that may define niche spaces for
species of Trichodesmium. Clade I and II concentrations correlated with each other in the
Pacific but not in the Atlantic, indicating that the two clades were limited by the same factors
in the Pacific while different factors were limiting the abundance of the two clades in
the Atlantic. Trichodesmium populations in the North Atlantic were more P stressed and
had higher N2 fixation rates than populations in the western Pacific. While nutrient concentrations
didn’t directly correlate with Trichodesmium concentrations, the contrasting
nutrient regimes found in the Atlantic and Pacific Oceans might influence distributions of
the two clades differently. Unraveling the differences among species of Trichodesmium
begins to explain their coexistence and enables us to understand factors controlling global
N2 fixation.
Description:
National Science Foundation
(NSF) Biocomplexity Program Grant (OCE-0323332); the Center for Microbial
Oceanography Research and Education (C-MORE), an NSF Science and Technology
Center (EF-0424599); the Woods Hole Oceanographic Institution (WHOI) Ocean Life
Institute (OLI) grant to J. Waterbury, and the WHOI Academic Programs Office.
Keywords:
Trichodesmium
;
Bacteria
;
Kilo Moana (Ship) Cruise KM0701
;
Kilo Moana (Ship) Cruise KM0703
;
Seward Johnson (Ship) Cruise SJ0609
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
Permalink