Viruses in marine food webs

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Viruses are the most abundant biological agents in marine plankton and have a tremendous potential impact on biological oceanographic processes, including material & energy flow as well as plankton diversity. New molecular methods to investigate diversity of host bacteria and viruses permit researchers to begin unraveling the relationships between virus and host diversity in marine plankton, and how it may affect overall rate processes. These molecular techniques include molecular fingerprinting of 16S rRNA and other genes for bacterial hosts, and pulsed field gel electrophoresis for virus communities. This project will use such approaches, along with other techniques, to study natural and experimental marine microbial systems and address basic hypotheses on the relationships between bacterial and viral communities. Study sites will include the Wrigley Time Series Site (WTSS) midway between Los Angeles and Catalina Island, and also richer coastal waters near Los Angeles and Catalina Island. Part of the project is continuation of an existing monthly time series at WTSS of virus abundance and virus community composition at 4 depths to 500 m, to augment other microbiological and oceanographic observations being made at that location with other financial support. In addition to the general time series databasing component which continues to provide valuable microbial community data in its own right, we will use this sampling to test hypotheses about viral control of specific common groups of marine bacteria, initially targeting the SAR 11 cluster, cyanobacteria, and marine alpha proteobacteria. Other focused experiments will also target these groups. SAR 11 and cyanobacteria are good targets because (a) they are ubiquitous and typically each makes up 5-30% of the bacteria (b) their members are very closely related to each other worldwide, yet distant from other known groups (c) an extensive database of 16S rRNA and 16S-23S intergenic spacer sequences for both groups is published (and also other genes in cyanobacteria), facilitating investigation of strain composition at high resolution without the need to culture the organisms (d) both groups are culturable, with the SAR11 group just recently isolated in dilution culture, with multiple strains reported. Short-term, more frequent sampling and experimental mesocosms will be used to examine community and specific subgroup dynamics on the generation time scale. The project has the added value of taking advantage of a unique time series of microbial diversity at an easily accessible marine site, suitable for further analysis such testing hypotheses relating diversity and stability in marine microbes. Samples (e.g. preserved virus concentrates, microbial DNA) will also be available for retrospective analysis. Exploratory investigation of virus diversity and activity in sediments is also included as a minor component. Broader impacts of this project include a training and education component with participation of underrepresented groups, enhancement of the research and education infrastructure, and planned broad dissemination of the results.