Award: OCE-1031783

Viruses are incredibly abundant in the ocean – about 10 billion in a liter of seawater. Most of these viruses do not infect humans or other animals, but bacteria. These bacteria play an ecological important role in the oceans. They take up nutrients, decompose organic matter, and influence gas concentrations in the EarthÆs atmosphere. Cyanobacteria, in particular, are a big part of the base of the marine food chain. Like plants on land, they take up carbon dioxide and use energy from the sun to create biomass. Viruses are thought to be a major source of mortality of cyanobacteria. Therefore, they are key component of understanding how big the base of the food chain is, as well as how much carbon dioxide is taken up by the oceans. Intellectual merit Despite their importance, we know very little about the diversity of marine viruses except that their diversity is very high. We do not know much about what that genetic diversity means; for instance, what genes control whether a virus can infect a particular type of bacterium or how fast the virus kills its host. However, this detailed information is essential to predict how viruses affect other marine organisms and ocean nutrient cycling. One of the best-studied groups of bacteria-infecting viruses in the environment is the cyanophages (viruses that infect cyanobacteria). This project used that system to ask how and why the diversity of marine viruses varies over time and space. During the project, we completed a five year time-series where we sampled cyanophages from both the Pacific and Atlantic coasts of North America. We sampled in such a way to facilitate comparisons between the locations and ask how other environmental and biological measurements correlated with cyanophage diversity in a sample. We then sequenced the genomes of a variety of the isolates to investigate which particular genes varied over space and time. We also used the genomes to search for particular genes that might act as "markers" of which bacterial hosts a virus could infect. Finally, we compared the genetic information with measured "traits" of the cyanophages – like which bacteria they infect and how fast they infect them. We found that like other organisms, cyanophages are highly seasonal. Some cyanophage types dominate in the summer months and others dominate in the winter months. We also found that there was very little overlap in the diversity of viruses in southern California and Rhode Island. We investigated these trends further and saw that the strength of UV at the time was highly correlated with changes in the virus community over time and space. This suggests that some viruses may be more or less susceptible to UV damage, but this hypothesis needs to be tested further. Finally, we saw that the genetic variation within a cyanophage "type" is highly restricted to particular genes and regions of the genome. The identification of these genes and regions can now be compared to measured traits of the cyanophages. Broader impacts This project has had broad impacts on a number of levels. First, the research has provided general insights into the distribution of marine cyanophage, which are key players in marine nutrient cycling. The virus collection, sequenced genomes, and other collected data is (or shortly will be) available to other researchers to aid in further investigations. Second, the project provided an outstanding learning experience for students. At UC Irvine, the project supported the training of 7 undergraduates, 2 PhD students, and 1 postdoctoral researcher. Finally, we developed a collaboration with Crystal Cove Alliance and the Crystal Cove State Park, to present the scientific research of this grant to K-12 and general public audiences through educational internships. As part of this program, four undergraduates and two MasterÆs students developed a hands-on "Build-A-Virus" activity about the role of marine microbes in the ocean, which they implemented...