Collaborative research: Characterization of Synechococcus-cyanophage interactions across phylogenetic and temporal scales

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Viral infection influences the flow of nutrients in the oceans and the diversity and structure of ecologically important microbial communities. Understanding which viruses infect which hosts is critical to understanding the exact impact of viruses, but there are still critical gaps in knowledge about how widely viruses can infect specific bacteria types and how this can change over time. This project includes the isolation and characterization of hundreds of co-occurring photosynthetic bacteria (cyanobacteria from the genus Synechococcus) and viruses that infect them (cyanophage) from Narragansett Bay, Rhode Island to assess the degree to which they can infect each other and identify specific genes that control cross-infection. DNA collected for over 10 years from Narragansett Bay is used to track Synechococcus and cyanophage communities to determine how virus-host interactions play out in shaping the diversity of natural Synechococcus and cyanophage communities over seasonal cycles and from year to year. This work provides knowledge of how individual viral-host interactions in a natural community can lead to the stable co-existence of particular species of viruses and bacteria in a coastal ecosystem over time. This project supports 15 undergraduate student researchers, a graduate student and a postdoctoral fellow who also receives training in effective practices in science teaching. Integration of the study’s results into undergraduate courses and outreach activities facilitates authentic opportunities for students to contribute to research and engagement of local junior and senior high school students.The team of scientists and students are conducting a phylogenetically-informed study of natural communities of co-occurring Synechococcus and cyanophage, a model tractable system in Narragansett Bay, to characterize phage-host interactions across different scales of diversity and time. The team’s goal is to isolate a large collection of ~100 Synechococcus and ~200 cyanophage from Narragansett Bay and to conduct infection assays and comparative genomics on these isolates. They employ amplicon sequencing of highly variable loci for both Synechococcus and cyanophage to characterize community dynamics across broad to fine genetic scales—ecotypes to within-species variants—for 10 years of archived monthly samples and a new weekly time-series over two years. These studies address the following three key questions: 1) Are there inherent boundaries of genetic relatedness (i.e. ecotype, species, or finer levels) at which the patterns of infection networks fundamentally shift from being mostly nested to mostly modular? (2) What are the underlying mechanisms and genetic loci that determine the boundaries of infection, i.e., host range and phage susceptibility? and, (3) How do host-phage interactions at different phylogenetic levels influence community structure over short (weeks to months) and long (year-to-year) time scales? Results from this project help to better understand how phytoplankton and bacterioplankton communities are shaped by viral predation and how host and phage diversity is created, maintained, and structured in the oceans.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.