Contributions of abundant bacterial groups to the flux of dissolved organic matter in the ocean

Bacterioplankton communities play a crucial role marine biogeochemical cycles because they mediate the flux of dissolved organic matter (DOM), which is equal to about half of primary production in the ocean. These bacterial communities are also known to be incredibly diverse and comprised of bacteria from several different phylogenetic groups. However, the relationship between microbial diversity and biogeochemical cycling remains unclear. My dissertation focused on determining the contributions of abundant bacterial phylogenetic groups to the biogeochemical flux of DOM in the ocean.; One specific goal if this dissertation was the identification and quantification of bacteria that assimilate the organic sulfur compound dimethylsulfoniopropionate (DMSP). DMSP can be hydrolyzed to produce dimethylsulfide (DMS), a sulfurous gas hypothesized to moderate changes in global temperature. However, most dissolved DMSP is assimilated into bacterial biomass, a process that satisfies nearly all of the bacterial S demand in the surface waters of the ocean. Since the biogeochemical fate of DMSP can affect either climate regulation or S transfer through marine food webs, it is important to identify bacteria that metabolize DMSP. To identify and quantify bacteria assimilating DMSP, I used a combination of micro-autoradiography and fluorescence in situ hybridization (Micro-FISH) to follow 35S-DMSP assimilation into marine bacterial communities.; In addition to DMSP flux, I also investigated the ecological activity of SAR11 bacteria. Gene sequences belonging to the SAR11 clade typically dominate 16S rRNA clone libraries from the ocean, and investigations with fluorescence in situ hybridization confirm that SAR11 bacteria often make up 25--35% of bacterioplankton communities. (Abstract shortened by UMI.)...