Date of Award


Degree Type


Degree Name

Doctor of Philosophy



Major Professor

Steven W. Wilhelm

Committee Members

Alison Buchan, Shawn R. Campagna, Karen G. Lloyd


Harmful cyanobacterial blooms (cyanoHABs) have detrimental effects on freshwater lakes and reservoirs around the world. CyanoHABs severely reduce water quality, altering the food web and disrupting fishing and tourism industries. In addition, many bloom-forming cyanobacteria have the capacity to produce potent toxins, making the negative impacts of cyanoHABs of ecological and economic importance and a serious public health risk. Microcystis spp., which are the typically dominating cyanobacteria in blooms, often produce thick scums, taste and odor compounds and the hepatotoxins, microcystin, implicated in water advisories, human and animal poisonings and drinking water shutdowns globally. Primarily driven by anthropogenic nutrient loading and climate change, Microcystis blooms are on the rise, not only increasing in frequency but also intensity. Nitrogen (N) and phosphorus (P) are considered the most important nutrients in driving bloom formation and persistence but historically management practices have solely focused on P abatements. Large inputs of N into the environment have now been tied to the increased prevalence of toxic Microcystis. To better understand the role of N and other environmental factors impacting the success and toxicity of Microcystis, a number of molecular techniques were employed to characterize bloom community dynamics and the physiology of Microcystis. Results from environmental studies generated new hypotheses about the role of heterotrophic bacteria in N-cycling and microcystin degradation, while observations from laboratory studies provided novel insight into the metabolism of N by Microcystis and subsequent microcystin production was proposed. Together, the findings presented here can be extrapolated to the natural environment and provide greater insight into the mechanisms that contribute to cyanoHAB expansion and toxicity.

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