Molecular ecology of bacteria associated with marine phytoplankton blooms

Bacteria are integral components of the marine food web with as much as 50% of the carbon fixed by phytoplankton channeled through the “microbial loop”. However, dissolved organic matter (DOM) flux into bacteria is highly variable and may be related to differences in bacterial species distribution and diversity in different (micro)environments.; This thesis examines bacterial community dynamics during the range of DOM and particulate organic matter (POM) associated with phytoplankton blooms, focusing on the marine Cytophaga-Flavobacterium (CF) group. CF are hypothesized as “particle-specialists” with important implications for particle degradation and the downward export of CO₂ to the deep ocean. The balance between particle degradation, regenerating CO ₂ via respiration, and burial, is a critical factor affecting climate change. Another environmental issue of societal concern is the association of human pathogenic bacteria with phytoplankton blooms; work related to the development of a quantitative method for the study of toxigenic Vibrio cholerae in the marine environment is presented here.; Changes in bacterial community composition were found to occur in concert with changes in bacterial metabolism during a Lingulodinium polyedrum bloom. The free- and attached-bacterial consortia were phylogenetically distinct with representatives of CF in each size fraction. Quantitative analysis of CF determined that these organisms reached high, albeit transient, abundance in the free-living phase during the bloom. Comparison of these data with CF dynamics during a diatom bloom further suggests that the ecological role and attachment behavior of CF may be related to the quality (bloom type) and quantity of organic matter in the sea. CF dynamics were also analyzed in the Southern Ocean during bloom and non-bloom conditions. These data suggest a high abundance and seasonal stability of CF communities despite widely varying hydrographic and biological regimes. Some association of these organisms with proxies of primary production (chlorophyll a) was observed, particularly with season. Overall, these studies suggest that CF are dynamic and abundant components of bloom bacterial consortia and extends the role of this group from particle- to DOM/polymer-specialist. These data have implications for the accumulation of dissolved organic matter and pathways of carbon flow during phytoplankton blooms.