Viruses in the plankton of the Rybinsk Reservoir

The role of autochthonous viruses in the regulation of bacterioplankton abundance and production was studied in the Rybinsk Reservoir. During the ice-free period, the number of virus-like particles varied within the range of (11.0-57.4) x 10(6) particles/ml. The virus to bacterioplankton abundance ratio ranged within 3.0-9.4. From 4 to 25% of bacterioplankton was infected by phages. A single infected cell contained up to 80 mature virus particles. The phage-induced bacterioplankton mortality in different parts of the reservoir constituted 3.7-41.8% (22.5% on average) of bacterioplankton daily production. Heterotrophic flagellates grazed from 7.6 to 68.8% (27.5% on average) of the daily bacterial production. Thus, along with flagellates, viruses are an important factor controlling bacterioplankton development in the reservoir.