Award: OCE-1031743

Marine microorganisms are enormously abundant (Fig 1), and they generate and process the large majority of ocean productivity, essential for ecosystem function. The least understood part of marine microbial systems are the viruses, whose many roles include infection and mortality of bacteria, archaea, and protists, but also the augmentation of functions of the system and transfer of genes. This project aimed to study the viruses as an integrated part of marine microbial systems. Studies centered around a well-established Microbial Observatory, the San Pedro Ocean Time Series (SPOT), and included monthly as well as daily studies of the changes in naturally-occurring bacteria, archaea, protists, and viruses. We used molecular genetic characterization of these microbes to track them, and microbial association network analysis to demonstrate interactions among these organisms. Thousands of statistically significant correlations (positive and negative) were found, indicative of many interactions. This project was the first to study these interactions this way. Among our findings, we found that the Association Networks of bacteria and viruses were much more interconnected than the networks of bacteria and protists. We interpreted this as indicative that viruses and bacteria have many specific interactions, where viruses can infect only one or a few bacteria; this contrasts to the less-specific interactions between bacteria and protists, whereby protists include grazing organisms that can consume many species of bacteria, or alternatively some protists are photosynthetic and can essentially feed multiple species of bacteria. The daily time series showed that changes from day to day were generally gradual, but many associations were found in the changes of the various microbial types. Most correlations were among bacteria or among viruses, but interestingly the correlations between bacteria and viruses tended to have time lags of 2-5 days, suggesting these correlations result from infection processes that take a few days to develop. Overall, this project considerably expanded our knowledge of marine viruses and their potential interacitons with the rest of the marine ecosystem. Broader impacts of the project included training of students from a local Los Angeles high school, USC undergraduates and graduate students, as well as technicians. Results have been integrated into websites for broad dissemination. Last Modified: 11/20/2014 Submitted by: Jed A Fuhrman