Doctoral Dissertations

Date of Award

12-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Alison Buchan

Committee Members

Steven Wilhelm, Sarah Lebeis, Gladys Alexandre

Abstract

Marine bacteria are key components of the marine food web and are influenced by the viruses that infect them. Viruses are the most abundant biological entities on the planet. Bacteriophages (phages) can cause lytic infections or form long-term relationships with their bacterial hosts, though aspects of the lysogenic to lytic switch remain poorly understood. Phages can manipulate host genetic diversity, metabolism, evolution and fitness, as well as offer host competitive advantage through conferring immunity to superinfecting phages. Phages can influence nutrient availability in ecosystems through cell lysis of their hosts. Lysogeny is prevalent in marine systems due to high incidence of temperate phage signatures from well-characterized bacteria. Exposure to stressors can effect prophage induction, though minute quantities of induction can occur in the absence of an obvious stressor. This phenomenon, described as spontaneous prophage induction (SPI), is now proposed to benefit lysogenized populations as a form of “biological weaponry”. SPI has historically been studied in E. coli, which is not ecologically relevant. Furthermore, many systems currently use lytic phages to study facets of phage-host interactions. Therefore, how temperate phages affect host physiology, modulate SPI, and manipulate metabolism is considerably less understood and investigated especially in nonmodel systems. Here, I used an environmentally relevant one-host-two-phage Roseobacter model system to characterize and elucidate the influence of lysogeny on host physiology and metabolism. I observed that temperate prophages influence physiology. Competition experiments reveal that our strains have increased fitness when grown together in biofilm but reduced fitness in liquid culture. Host range studies determine very high host specificity of our phages, and highlight modulation of growth dynamic, cell size, biomass and SPI according to vessel type, culture volume and substrate. We show that discrete metabolites are responsible for observed differences in the metabolome and lipidome between our strains when grown on standard marine media, glutamate or acetate. In summary, these findings offer insight into key genetic and metabolic mechanisms of host-phage dynamics as they relate to host fitness, evolution, and regulation of nutrients into the marine environment. This work helps elucidate the biological and ecological factors affecting such phage-host systems in nature.

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