9634028 FUHRMAN Although viruses are now thought to be major players in marine food webs, we know very little about what happens to viral "biomass" in these food webs. The subject is important because a significant fraction, on the order of 10s of %, of total marine primary productivity passes through the viral "compartment." While it has been assumed that this matter is utilized by bacteria, there have been no studies of the actual fates of this material nor of the rates with which it is transformed or decomposed. This project will use a combination of laboratory and field studies to determine the fates of viral matter and cell debris released when viruses lyse an organism, and the rates by which this matter travels through different routes in the microbial food web. A major method to be used is radiolabelling of the products of viral infection, purification of the products, and then addition to fresh seawater. The project will examine the interactions with bacteria, phytoplankton, and other protists. Of particular interest is the variability of these processes, within communities and between different times and places. It is also proposed to develop an approach to label natural viruses with colloidal gold and then use an electron microscopy-based analysis analogous to "isotope dilution" to estimate simultaneously the production and loss rates of each labelled viral morphological type. The information should improve our ability to form conceptual and numerical models of marine microbial food webs. It also should prove useful in the more general study of the turnover of marine dissolved organic matter (to which viruses operationally belong), which now appears to be of considerable significance in global geochemical cycles. ***
