Microbes make up the majority of the biomass in the ocean and viral mortality is one of the main ecological factors determining the diversity, abundance and turnover of microbial taxa. Yet, in spite of the known overall importance of viruses, the dynamics of their interactions with their specific microbial hosts remain poorly understood. This project will characterize viral strategies for survival and interaction with their hosts in the ocean, with the goal of enabling a better understanding of the conditions under which viruses can effectively control bacterial populations. The work will generate and integrate diverse data types, ranging from quantification of specific interactions, environmental dynamics of microbial hosts and their viruses, and comparative genome analysis. While the project focuses on the coastal ocean of New England, the approaches and findings will be applicable to the larger field of marine microbial ecology, to other virus/host systems in nature and to engineered systems. This project will fill a gap in current microbial ecology curricula by creating a bioinformatics module to provide training in large-scale sequence data collection and analysis. The module will be refined through testing during an annual course in Nicaragua and will be broadly accessible in the US and internationally. The close collaboration, throughout this project and its associated outreach, between two laboratories with complementary research strengths will provide highly interdisciplinary training for undergraduate students as well for two graduate students.

Viruses and their microbial hosts have co-evolved over billions of year and shape the ecology of the ocean in many ways. Broadly, understanding the mechanisms and emergent properties of virus-host interactions will allow for better understanding and modeling of biogeochemical cycles and the diversity of microbes at the population and genomic level. The guiding hypothesis of this project is that the prevalence of each of different viral strategies is probabilistic and linked to host availability, environmental parameters, and frequency-dependent competition with other virus strains for available hosts. This research will address four aims that characterize how viruses interact with their hosts in the dilute ocean environment by (1) quantification of ecological tradeoffs between specialist and generalist viral strategies, (2) estimation of the prevalence of dual lytic/lysogenic strategy in marine viruses, (3) identification of host surface receptors of particular viruses and examination of genetic signatures of distinct viral strategies in virus and host genomes, and (4) identification of genetic and metabolic interactions between virus and host genomes. This study takes advantage of a model system with the largest available collection of viruses and hosts for which host range and genome sequences have been determined. This work will provide fine-scale analysis of host and phage genomic diversity and abundance in this model system, while at the same time estimating host-range and co-infection, all of which represent important, poorly constrained parameters in virus-host interactions. Finally, this project complements the large number of studies that have looked at single host-virus interactions, metagenome sequencing, and assessment of viral impact on microbial production.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Michael Sieracki
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Massachusetts Institute of Technology
United States
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