ABSTRACT

The evolutionary ecology of virus-host interactions are key to understanding viral-induced mortality rates in marine ecosystems, as the pattern and dynamics of virus-host interactions will ultimately determine the influence of viruses on nutrient cycling. Recent studies suggest that the diversity and composition of marine viruses appears to vary over time and space. The goal of this research is to move beyond simply documenting biogeographic patterns in marine viruses and to begin to ask why the genetic composition of marine viruses varies over time and space. Part of the challenge in doing this is that little is known about how the genetic diversity of a marine virus relates to its phenotype. To address this challenge, the PIs propose to take an isolation approach, using lytic cyanophages that infect marine Synechococcus as a model system. In this way they can compare the genotype and phenotype of each virus isolate.

Intellectual merit
This project will test the overarching hypothesis that the biogeographic patterns of marine cyanophages depend on the particular gene examined, as different parts of the genome, and ultimately, the phenotypes that they encode are under different evolutionary pressures. To do this, the investigators will use a three-pronged approach. First, they will identify "host range genes", or genetic markers of cyanophage host range (the particular hosts that a phage can infect). Second, they will conduct a time-series study of cyanophage isolates from the Pacific and Atlantic coasts of North America to compare the temporal and spatial biogeography of three types of cyanophage genes (conserved core genes, host range genes, and host-derived genes). To test that these patterns hold for cyanophage generally, and not just for culturable isolates, the investigators will examine the diversity of the conserved core gene directly from environmental DNA using 454 sequencing technology. Finally, using isolates from the time-series, they will characterize cyanophage phenotypes. For instance, they will determine the survival rates of cyanophage outside of the host under different temperatures. The investigators will also assay host range by testing the ability of each isolate to infect a diverse range of Synechococcus strains. This study will take advantage of the extensive cyanophage collections in Marston and Martiny's labs. Marston has been isolating cyanophage from Rhode Island waters for 10 years, and Martiny has been collecting isolates off the southern California coast for 2 years. It will also build on a completed long-term chemostat experiment from a prior NSF collaborative project and build on a currently funded 1-yr time-series in CA (a RAPID grant to Martiny to sample through the El Niño year). In addition, the project will leverage the whole genome sequencing of nine cyanophage genomes, which are already underway as part of the Broad-GBMF Phage, Virus, and Viriome Sequencing Project.

Broader impacts
This project will have broad impacts on a number of levels. First, the research will provide general insights into the evolutionary ecology of marine bacteriophage, which are key players in marine nutrient cycling. In addition, identifying genetic markers of a phage's host range would be extremely useful for future studies that focus on the role of phage in marine biogeochemical cycles. Second, the project will provide an outstanding learning experience for students at a variety of levels. In total, this project will support the training of 8 undergraduates per year, 1 PhD students, and 1 postdoctoral researcher. Two undergraduates per year (at least one a minority student) will participate in a science-education internship with the Crystal Cove State Park to develop exhibits, talks, and activities to showcase marine science at the Park; these materials are expected to benefit more than 50,000 visitors per year. Finally, aspects of this research will be developed into inquiry-based laboratory exercises at RWU and into K-12 curriculum materials for use in UCI's new BS in Teaching Science.