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Environmental and genomic insights into marine virus populations and communities

University of British Columbia

Marine viruses are the most abundant and genetically diverse biological entity in the oceans. Viruses infecting phytoplankton have a role in maintaining phytoplankton diversity, but also affect the cycling of carbon and nutrients through the microbial loop, which has substantial implications for the marine food chain and the planet’s climate system. It has also become evident that viral replication is affected by environmental conditions. In turn, viruses appear to possess a repertoire of metabolic genes to compensate for environmental adversities. However, it is not well understood how environmental variables affect viral replication in the environment or what the role of their genetic repertoire is in the selection to replicate. This thesis investigates the abundance and genetic diversity of viruses, the composition of viral communities and how the dynamics of viral replication is affected by in situ environmental conditions in four projects which are presented in Chapters 2, 3, 4 and 5. Chapter 2 describes the influence of environmental variables on the variation in viral and host abundance, and how this dynamic changes among different environments. Chapter 3 shows that phycodnaviruses infecting prasinophytes have a highly variable genetic repertoire with several metabolic genes of diverse origins. This genetic variability is reflected in their distribution in the environment, indicating selection on viruses. Chapter 4 establishes an approach to study cyanomyovirus communities and their associated genetic repertoires in the environment. It shows that the distribution of cyanomyovirus ecotypes on temporal and spatial scales is a function of environmental variables. Chapter 5 unveils a considerable mismatch between free cyanomyovirus communities, representing the seed bank, and replicating cyanomyoviruses in the cellular fraction. The emergence of replicating viruses out of the viral seed bank is highly variable and affected by environmental factors. In conclusion, total viral abundance as well as the community composition of specific virus types show a relationship to environmental variables. The genetic repertoire of viruses appears to be an adaptation to selection pressure and specific viruses can occupy environmental niches that are not only defined by the presence of susceptible hosts but also by a virus's ability to compensate for adversities.

Text

2017-12-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/61997

Oceanography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/