RESUMO
The ciliates Paramecium bursaria contain endosymbiotic green algae Chlorella spp. in their cytoplasm. The algae isolated from P. bursaria are sensitive to large DNA-containing viruses of the family Phycodnaviridae. The type virus of this family is PBCV-1 (Paramecium bursaria Chlorella virus). Investigation of the total DNA of P. bursaria clones by pulse-field electrophoresis (PEP) revealed a pronounced band on PEP profiles of some P. bursaria clones; the band was formed by DNA molecules of approx. 300 kb. This band probably contained the DNA of chlorella virus. Two approaches were used in the present work to confirm this hypothesis. Microbiological tests were used to scan a collection of P. bursaria clones for specific types of viruses; the 300-kb band was revealed only in the PEP profiles of virus-containing clones. Blot hybridization of P. bursaria total DNA separated by pulse-field electrophoresis with the virus-specific probe revealed that the band under study contained the DNA of a chlorella virus. Paramecium clones were shown to contain approx. 10(5) copies of nonintegrated viral DNA.
