Bacteria-bacteria antagonism on marine organic particles and its biogeochemical implications

Bacteria are a significant force shaping the marine food web and the ocean's biogeochemistry. Individual cell activity occurs at millimeter scales with bacterial surface enzymes altering the size and composition of organic matter with which bacteria interact. We now have greater appreciation of diversity of bacteria and how bacteria differ in their capacities to degrade organic matter. Bacteria-organic matter interactions at the small-scale leads to large-scale changes in the ocean's chemistry and flux of organic matter.; The objectives of this thesis were to examine the microscale structure in which bacteria-bacteria and bacteria-particulate organic matter (POM) interactions occur, how bacterial species are distributed at that scale, and whether antibiosis leads to small-scale patchiness of bacterial species. To this end, protocols were developed to visualize the proteineous component of the POM field and to measure bacterial species richness and composition in a single microliter of seawater. A model system was developed to study antibiosis on particles.; Proteineous particles were ubiquitous at the study sites. These particles and other components of the organic matter field are now believed to form a thin gel matrix in the pelagic ocean. Bacteria readily colonize the proteineous particles. Patchy distribution of bacterial species were found at the microscale, and both patchiness and richness level increased with increase POM. Antibiosis was a common phenotype amongst marine pelagic bacteria. The majority of inhibitory interactions involved particle-associated bacteria against free-living bacteria. While antibiotic production detected in all major phylogenetic groups examined, it was more common in γ-proteobacteria. An Alteromonas sp. was used as a model bacterium that produced antibiotics only on surfaces, to examine the potential role of antibiotics in regulating bacteria-bacteria and bacteria-POM interactions. The molecules produced by the Alteromonas affected metabolism and physiology of other marine bacteria, and it altered the structure of bacterial community colonizing a model particle system. Sub-lethal concentrations of the antibiotic altered bacteria-diatom interactions. These variations and changes of small-scale bacteria species composition may in turn alter the degradation of organic matter, as well as diatom species dynamics, and thereby organic matter fluxes and biogeochemistry in the ocean.