Microbial Community Dynamics of a Microcystis Bloom

Harmful algal bloom events are notoriously associated with massive economic and environmental consequences, causing wildlife and human health risks. As these blooms increase in occurrence, duration, and severity around the world, it is essential to understand conditions leading to bloom formation and why they persist. Abiotic factors such as nutrients are commonly considered in bloom dynamics, but biotic interactions with co-occurring microbial species and viruses must also be taken into account. Harmful algal blooms dominated by the cyanobacterial genus Microcystis occur in bodies of water around the world and provide an ideal system in which to study top-down controls on bloom dynamics. Co-occurring cyanobacteria, photosynthetic eukaryotes, and heterotrophic bacteria can all directly influence Microcystis growth, through competitive or mutualistic interactions. Viruses are also often implicated in the top-down control of Microcystis bloom systems both directly and indirectly, and evidence suggests that viruses have potential to influence bloom dynamics. There have been observations of Microcystis phage infections in previous bloom events in Lake Erie, USA, and Lake Taihu, China, directly affecting Microcystis populations. Viruses can also act as indirect controls by infecting potential competitors such as photosynthetic eukaryotes, allowing for Microcystis to have the competitive advantage. The methods of studying Microcystis blooms are equally important as the hypotheses themselves. Molecular sequencing data can provide a wealth of knowledge not only on Microcystis physiology and activities, but also the identity and functions of the microbiome. Careful consideration of available analysis tools is required to accurately characterize these relationships and provide a more holistic view of a Microcystis-dominated harmful algal bloom. A full understanding of these blooms cannot come from evaluating Microcystis in isolation, as it does not exist in isolation in the natural environment. This dissertation seeks to fill some of these gaps in the knowledge by characterizing the viral and host community in natural Microcystis blooms.