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 2013
Description:
Marine phytoplankton are the principal producers of oceanic dissolved organic matter (DOM),
the organic substrate responsible for secondary production by heterotrophic microbes in the sea.
Despite the importance of DOM in marine food webs, details regarding how marine microbes
cycle DOM are limited, and few definitive connections have been made between specific
producers and consumers. Consumption is thought to depend on the source of the DOM as well
as the identity of the consumer; however, it remains unclear how phytoplankton diversity and
DOM composition are related, and the metabolic pathways involved in the turnover of DOM by
different microbial taxa are largely unknown. The motivation for this thesis is to examine the
role of microbial diversity in determining the composition, lability, and physiological
consumption of marine DOM. The chemical composition of DOM produced by marine
phytoplankton was investigated at the molecular level using mass spectrometry. Results
demonstrate that individual phytoplankton strains release a unique suite of organic compounds.
Connections between DOM composition and the phylogenetic identity of the producing organism
were identified on multiple levels, revealing a direct relationship between phytoplankton diversity
and DOM composition. Phytoplankton-derived DOM was also employed in growth assays with
oligotrophic bacterioplankton strains to examine effects on heterotrophic growth dynamics.
Reproducible responses ranged from suppressed to enhanced growth rates and cell yields, and
depended both on the identity of the heterotroph and the source of the DOM. Novel relationships
between specific bacterioplankton types and DOM from known biological sources were found,
and targets for additional studies on reactive DOM components were identified. The physiology
of DOM consumption by a marine Oceanospirillales strain was studied using a combined
transcriptomic and untargeted metabolomic approach. The transcriptional response of this
bacterium to Prochlorococcus-derived DOM revealed an increase in anabolic processes related to
metabolism of carboxylic acids and glucosides, increased gene expression related to
proteorhodopsin-based phototrophy, and decreased gene expression related to motility. Putative
identification of compounds present in Prochlorococcus-derived DOM supported these
responses. Collectively, these findings highlight the potential for linking detailed chemical
analyses of labile DOM from a known biological source with bacterioplankton diversity and
physiology.
Description:
Financial support for this work was provided by the National Science Foundation Center
for Microbial Oceanography: Research and Education (award #EF0424599 and
#DBI0424599) including generous contributions from the EDventures program, the
Gordon and Betty Moore Foundation (grant #1711), and a student research grant from the
Coastal Ocean Institute at the Woods Hole Oceanographic Institution.
Keywords:
Seawater
;
Organic compound content
;
Marine phytoplankton
;
Kilo Moana (Ship) C-MORE BLOOMER Cruise
;
Ka`imikai-o-Kanaloa (Ship) Cruise
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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