Doctoral Dissertations

Orcid ID

Date of Award


Degree Type


Degree Name

Doctor of Philosophy



Major Professor

Steven Wilhelm

Committee Members

Todd Reynolds, Tim Sparer, Erik Zinser, Brad Binder


Viruses in aquatic systems are a major source of mortality to microbial life, influencing the structure of communities, nutrient cycling, and evolution. Many lineages of eukaryotic algae have been visually confirmed to be infected with viruses, but only a small subset have isolates. Of those where viruses are isolated, an incredible amount of diversity exists, including differences in genome composition, particle sizes, and infection strategies. Under certain conditions specific populations of eukaryotic algae can bloom, which cause millions of dollars in losses. The harmful brown tide bloom forming Aureococcus anophagefferens negatively influencing sea grass beds and these algae are potentially toxic to shellfish. Viruses have been implicated in termination of these blooms. A viral isolate, Aureococcus anophagefferens Virus (AaV), has been characterized over the past decade. This work continued characterization of the system through characterization of the particle itself, development of new tools to study the ecology of AaV, and by studying how abiotic factors influenced the infection cycle. The particle has the same conserved capsid structure as other related icosahedral viruses and contains at least 43 proteins. Of those packaged, some were found in particles of similar viruses, while others (i.e. sugar-degrading proteins) were unique. The study provided novel insight into evolutionarily conserved aspects of these particles, as well as those that are system specific. To understand the role of Aureococcus infecting viruses in natural blooms, we developed reliable methods to enumerate total (quantitative PCR) and infectious (plaque and most probable number) particles. Using these tools, the influence of irradiance levels and N:P ratios on the infection cycles were studied. At light levels which reduces growth either caused by acclimation or light shift experiments, an increased latent time and a reduced burst size was observed. Unlike the reduction of irradiance levels, only acclimating to N:P ratios where growth was reduced, negatively influenced the infection cycle. Overall, this work provides novel insights into the A. anophagefferens AaV system and developed new tools to study it in the environment. As each algal virus system studied is unique, more research should be conducted to isolate and characterize novel systems.


Chapter 3 was previously published in Plos One. The citation for this work is: Gann ER, Gainer PJ, Reynolds TB, Wilhelm SW. (2020) Influence of light on the infection of Aureococcus anophagefferens CCMP 1984 by a “giant virus”. PLOS ONE15(1): e0226758.

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