Cyanobacteria associated bacteriophage communities across scales of spatial, temporal and environmental change

Viruses are prevalent in most, if not all, environments on Earth. They contribute significantly to global genetic diversity and interact with organisms in all branches of life. Although the field of viral ecology has made great strides in understanding role of viruses in ecosystems functions, the complexity and diversity of viruses have made them particularly difficult to characterize. This dissertation contributes to the overall understanding of viral ecology through investigation into bacteriophage responses to varying scales of change utilizing unique characteristics of two different environments. Chapter 1 introduces key concepts in viral ecology that will be addressed in the body of the dissertation. Chapter 2 assesses virus-host dynamics in situ by following the dynamics of three cyanobacterial viruses and the cyanobacterial population over two summer seasons in Fayetteville Green Lake and Round Lake, neighboring lakes that are biogeochemically similar. This study found consistent trends in cyanophage abundance between lakes, but annual variability and a weak relationship between the abundance of virus and host populations. Chapter 3 focuses on the marine environment to examine how a viral community responds when exposed to sharp environmental change in the form of cyanobacterial aggregation collapse. This study observed both lytic and lysogenic phages of bacteria known to be associated with Trichodesmium colonies, showing that viruses capable of both infection strategies respond to environmental change. Chapter 4 returns to Fayetteville Green Lake to probe temporal aspects of virus population dynamics on extended timescales. This chapter examines signatures of cyanobacterial viruses in over 180+ years of the lake's history through examination of signatures of cyanobacterial virus genes present within chronologically distinguishable, undisturbed sediment cores. This study found patterns of representation of genetic signatures of cyanophages that suggest a dynamic population of cyanophages that have varying evolutionary trajectories within the lake. Through providing insights into how viral communities change over several scales of inquiry, the work presented in this dissertation adds to the growing body of knowledge of viruses in the environment and offers unique insights that will greatly contribute to the field of viral ecology.