Elucidating the Impact of Roseophage on Roseobacter Metabolism and Marine Nutrient Cycles

As the most abundant biological entities in marine environments, viruses are an important component of marine food webs. The activity of viruses contributes significantly to the mortality of marine microorganisms, ultimately influencing biological function and chemical composition of aquatic systems by impacting species composition and flow of carbon, nitrogen and other nutrients. Despite the growing recognition that viral activity contributes to marine biogeochemical cycles, the extent to which virus infection reshapes host metabolism and the effect of this alteration on the composition of host lysate remains poorly understood. Additionally, the degree to which natural bacterioplankton communities metabolise the released lysate material remains an open question. In this study, we use a Roseobacter lysogen, Sulfitobacter sp. CB2047, and its infecting phage as models to examine phage-host interactions in the marine environment. Specifically, this dissertation investigates the effect of superinfection of Sulfitobacter lysogens on resident prophage induction and its effect on accelerating the transfer of genetic material and increasing microbial genetic diversity. This work also characterizes the effect that phage infection has on reshaping host metabolic processes to provide building blocks for the synthesis of new virion particles and how this redirection of host metabolism affects the composition of material released as virus lysate after cell lysis. Finally, this dissertation examines how virus-derived lysates are metabolised by members of the natural bacterioplankton community and how this affects the consuming population’s metabolism. Results from our studies indicate that superinfection of Sulfitobacter lysogens increases prophage induction ~24-fold and increases Sulfitobacter diversity by up to 2%. Our results also indicate that phage infection significantly elevates host metabolism, redirecting ~75% of host resources from energy production to the production of new phage virions. Additionally, our results demonstrate that viral lysates are rich in small, labile nutrients that are readily utilized by natural bacterioplankton communities, significantly increasing their metabolite pools and nutrient turnover. Overall, this research provides an enhanced framework for understanding the role of marine viruses in shaping microbial genetic diversity and characterizes the impact that virus infections have on redirecting host metabolism as well as the availability and metabolism of nutrients to natural bacterioplankton communities.