Thesis

The effects of reduced phosphorus compounds on bacterial populations in the soil

The characterization of bacterial metabolic pathways oxidizing phosphite have been characterized. However, bacterial oxidation of phosphite in the environment and its impact on the biogeochemistry has been largely ignored. In this study I attempted to answer 1) do excessive phosphite concentrations in soil significantly alter bacterial populations in soil; and 2) to what extent do these changes affect the overall bacterial community. To answer these questions we performed a soil competition assay, utilizing isogenic reporter bacteria (1 oxidizer and 1 non-oxidizer of phosphite) that were inoculated into an intact soil environment and recovered them from the same soil environment, and tracked their population decreases and increases over time in relation to different phosphorus treatments, including phosphite. We saw a significant change in our reporter bacteria in the phosphite treatment, and saw potential phosphate recycling occur via phosphite oxidizing bacteria utilizing phosphite as a sole phosphorus source and subsequently recycling the phosphate into the soil environment for phosphite nonoxidizers to use as a sole phosphorus source. Denaturing Gradient Gel Electrophoresis also displayed significant change in bacterial populations over time in the soil sample used for the soil competition assay. My results indicate that excessive dumping of phosphite into soil can lead to major bacterial population change, the exact effects from this change still need to be investigated by future researchers, which directly will contribute to the little known phosphorus cycle.

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