Doctoral Dissertations

Date of Award

8-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Steven W. Wilhelm

Committee Members

Alison Buchan, Erik Zinser, Loren Hauser, Jennifer DeBruyn

Abstract

Cyanobacterial harmful algal blooms (cHABs) degrade freshwater lakes worldwide. Accumulation of nuisance biomass and production of noxious secondary metabolites can result in an expansive impact on both lake ecology and the surrounding communities. The cHAB forming organism Microcystis aeruginosa is known to produce the toxin microcystin, a compound nicknamed “fast death factor,” which has been implicated in animal poisonings and human liver failure and cancers. M. aeruginosa inhabits a wide range of freshwater lakes around the world, such as Lake Erie (USA/Canada) and Lake Tai (Taihu, China), and is often a dominant member of bloom communities. Such systems are well-studied paragons of annual bloom events which have expanded both in size and duration in recent years. Decades of research on these two lakes point to eutrophication, specifically nitrogen (N) and phosphorus (P) loading and rising global temperatures as keys to the success of Microcystis spp. in the environment. Nevertheless, it is unknown how these environmental factors interact with microbial communities to contribute to bloom formation. To better understand these complex interactions, a series of targeted and community genomic and transcriptomic studies were performed. Due to the exploratory nature of these studies, results from each were largely in the form of new hypotheses about the Microcystis system. Specific findings support the established hypothesis that microbial community function is independent of community structure, at both that the DNA and mRNA levels. Novel hypotheses were also generated as a result of these exploratory studies, including that nutrient availability, specifically the availability of nitrogen and phosphorus, may drive activity of transposable elements across the genome of Microcystis. Taken together, this work represents a new foundation for future exploration of the success of Microcystis in freshwater lakes, and will lead to a series of new empirical studies to test the hypotheses presented herein. This in turn has led to the advancement of understanding of the microbial interspecies relationships of freshwater cHABs at the intersection of environmental biogeochemistry.

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