Viral Infection of Picocyanobacteria in the Rybinsk Reservoir During the Freezing Period

The abundances of virioplankton and planktonic picocyanobacteria in deep and shallow water sites of Rybinsk Reservoir during the freezing period (water temperature 0.3–0.9°C) varied from (37.1 to 84.1) × 10 6 ((57.3 ± 2.1) × 10 6 , on average) particles/ml and from 13.5 to 75.0 × 10 3 ((48.7 ± 3.4) × 10 3 , on average) cells/ml, respectively. The fraction of picocyanobacteria with viruses attached to their cell surface was 6.5–29.0% (12.0 ± 0.8%, on average). The proportion of visible infected cells was 0.7–7.6% (2.2 ± 0.3%, on average) of the numbers of picocyanobacteria. It is likely that viruses play an important role in the regulation of picocyanobacteria abundance during the freezing period.