Aspects of the ecological role of bacteriophages

The discovery of high viral abundance in marine waters prompted investigation into the ecology of Chesapeake Bay virioplankton. The annual dynamics of virioplankton abundance was observed at six stations traversing Chesapeake Bay. Average viral abundance in Chesapeake Bay water samples was ;Direct counting established that virioplankton abundance changed seasonally; however the proportion of viruses seen in direct counts which are infective was unknown. This is an important consideration for determining the importance of lysis in regulating host abundance. The differential effects of sunlight on bacteriophage viability and structure, was examined in a microcosm study utilizing two autochthonous bacteriophages, CB 7;It has been postulated that viral infection may serve as a significant agent of bacterial mortality. Another theory is that viral infection influences the clonal diversity of host communities. Such an ecological role would predict that virioplankton populations are seasonally and spatially unstable in species composition. To test this, the population dynamics of Chesapeake Bay virioplankton was observed, using pulsed-field gel electrophoresis (PFGE), at six stations in the Bay for one annual cycle. PFGE revealed several distinct bands, ranging from 50 to 300 kilobases. Comparisons of electrophoretic banding patterns from different water samples indicated that virioplankton populations changed according to geographical location, time and the degree of water column stratification.;While PFGE analysis identified large scale changes in the composition of virioplankton populations, hybridization analysis revealed changes in the abundance of specific virioplankton strains. The spatial and temporal dynamics of specific virioplankters supports the behavior predicted from a model for viral control of phyto- and bacterioplankton diversity. Results indicate that Chesapeake Bay virioplankton populations are unstable in composition, supporting the theory that virioplankton maintain the clonal diversity of host populations.