Opening the black box of viruses in aquatic systems

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At abundances of 106 to 108 ml-1, viruses are the most numerous and diverse "life" in the oceans. End-to-end, they would stretch 107 light years, farther than the nearest 60 galaxies. It is estimated they infect ~1023 cells s-1, and kill 10 to 20% of the ocean's biomass daily, resulting in 6 to 26% of carbon fixed by phytoplankton passing through the viral shunt. Clearly, viruses are major players in mortality, nutrient cycling and structuring planktonic communities; yet, the composition and function of viruses in aquatic systems is largely unknown. The long-term goal of my research is to understand the enormous genetic and biological diversity of aquatic viruses and their impact on ecosystems. The proposed research will advance our understanding of aquatic viruses and their function through virus discovery and quantifying their impact on mortality. ******In the virus-discovery theme, traditional approaches will be used to isolate novel viruses that infect ecologically important taxa, while state-of-the-art single-virion genomic and metagenomic approaches will be employed to characterize the isolates and in situ virus communities. Four projects comprise the viral discovery component: 1) Isolation and characterization of new host-virus systems for ecologically important microbial taxa will provide model systems for studying host-virus interactions. We will focus on giant viruses, because metagenomic data indicate they are widespread in aquatic systems, but there are few in culture infecting planktonic protists. 2) We will employ single-virion genomic technologies to sequence uncultured representative viruses from a range of natural environments. This will help close the sequence space for aquatic viruses and provide genomic context for short-read metagenomic data. 3) Metagenomic analysis of aquatic RNA virus communities will reveal the most abundant RNA viruses across a range of aquatic systems, allow the assembly of novel genomes, and provide context to targeted amplicon sequencing data from other studies. 4) Determining the composition of viruses associated with major taxa of zooplankton and their potential impact.******The second theme explores the impact of viruses on microbial mortality. Using a targeted sequencing technique to estimate taxon-specific viral mediated mortality across systems we will determine which prokaryotic and eukaryotic microbial taxa are most subject to viral lysis, and test the hypothesis that most lysis is occurring in productive but relatively rare members of the community.******Collectively, this research program advances our understanding of viruses in aquatic systems by bringing new virus-host systems into culture, characterizing viral communities and determining taxon-specific lysis in microbial communities.