Microbial Production and Consumption of Marine Dissolved Organic Matter

Jamie Becker, Ph.D., 2013
Daniel Repeta & Edward DeLong, Advisor

Marine phytoplankton are the principal producers of dissolved organic matter (DOM), fueling secondary production in the sea.  Producer and consumer identity are likely important for DOM cycling, however it is unclear how phytoplankton diversity and DOM composition relate and the metabolic pathways involved in DOM turnover are largely unknown.  The motivation for this thesis is to examine the role of microbial diversity in determining the composition and physiological consumption of marine DOM.  The chemical composition of DOM produced by marine phytoplankton was investigated at the molecular level, revealing a relationship between phytoplankton phylogeny and DOM composition at multiple diversity levels.  Phytoplankton-derived DOM was also employed in growth assays with oligotrophic bacterioplankton strains.  Novel relationships between bacterioplankton and DOM sources 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.  Collectively, these findings highlight the potential for linking detailed chemical analyses of DOM from known biological sources with bacterioplankton diversity and physiology.