Viruses are the most numerous component of the plankton, often ten-fold more abundant than their procaryotic and eucaryotic counterparts. In most aquatic systems, a steady state exists between bacteria and viruses without collapse of the bacterial or cyanobacterial host populations. Because the infectivity of phages decays relatively quickly in surface waters, there must be an equally rapid re--supply of new phages. However, the cyanobacteria (and perhaps the heterotrophic bacteria) are largely resistant to phage infection. How can there be constant phage production in the presence of a resistant host population? The hypothesis tested in this project is that bacterioplanlkon persist in the presence of high viral abundance because lytic phages have selected for a community that is resistant to infection. Alternatively, bacterioplankton (including cyanobacteria) persist in the presence of high viral abundance because of homo-immunity conferred by lysogeny and pseudolysogeny. To test these hypotheses, the project will work toward the following objectives: 1. To determine the relationship between lytic, pseudolysogenic, and lysogenic modes of existence using isolates in culture. 2. To determine if the transition between lysogeny and lytic existence occurs in natural microbial populations such as those occurring in Tampa Bay. 3. To determine the prevalence of lysogeny amongst marine Synechococcus isolates. We will examine a series of phycoerythrin containing and non-PE containing strains from culture collections as well as our own isolates from the Gulf of Mexico for the presence of prophage by mitomycin C and/or UVC exposure, and will use these strains to understand the process of lysogeny in cyanobacteria. 4. To determine if lysogeny or pseudolysogeny is the mechanism of resistance in natural Populations of Synechococcus. The results obtained from this study may substantially alter our understanding of viruses in the Microbial Loop, from lytic entities that perpetually attack their hosts to co-participants in a highly evolved symbiosis that may switch from virulence to temperate existence in response to environmental cues.
