Doctoral Dissertations

Date of Award

5-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Steven Wilhelm

Abstract

The study of viral ecology in aquatic microbial communities is a relatively young field. The expanse of viral diversity has yet to be fully understood and there are still numerous questions concerning the roles that viruses play in aquatic communities and the constraints placed on these roles by co-occurring biotic and abiotic factors. Understanding how viruses interact with their hosts and how these interactions affect aquatic systems as a whole is vital to comprehending global-scale influences of viruses. In aquatic systems, and particularly in the world's oceans, microbes drive the cycling of important elements such as C, S, N and P; viruses, through a predatory, top-down effect, are major drivers of this process. As a first step toward examining virus-host interactions, the isolation and identification of viral strains is vital as it provides a foundation for further studies.Through the adaptation of Koch's postulates and use of electron microscopy, an Aureococcus anophagefferens-infecting virus was isolated, clarifying confusion from earlier conflicting results. Subsequent analyses focused on the total viral population across large spatial scales, covering 3 major oceanic regimes. Total viral abundance and production rate were measured along with other biotic and abiotic factors such as sizefractionated chlorophyll a, total cell abundance, bacterial biomass production rate, salinity, temperature, etc. These variables were examined individually, pair-wise, and collectively to elucidate any significant trends and relationships among them. Results indicated three distinct trends. First, in the Sargasso Sea, viral parameters were fairly predictable. Second, in the North Atlantic, a threshold effect was reached. And third, in the Western Pacific a changing microbial community structure is likely a major influential factor.Lastly, a search for a new phylogenetic marker for viruses examined the major capsid protein (MCP) gene sequences of viruses from the North Atlantic as a proxy for the diversity of Phycodnaviridae (a major family of eukaryotic algae-infecting viruses). This analysis provides a foundation for future work aimed at teasing apart viral populations so that relative abundances and production rates can be determined and compared with total abundances and rates as well as with other parameters of the ecosystem in question.

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