Molecular Investigation of Paramecium bursaria Endosymbiotic Algae: the First Records of Symbiotic Micractinium reisseri from Kamchatka

Paramecium bursaria is a symbiotic ciliate species which cells contain hundreds of algae enclosed in perialgal vacuoles. The aim of the present study was to identify endosymbiotic algal strains of P. bursaria and to define the geographical distribution of the identified species. We analyzed symbiotic strains of P. bursaria originating from distant geographical locations and housed at the Culture Collection of Ciliates and their Symbionts (CCCS) at St. Petersburg University. Based on the obtained results, we identified these strains as Micractinium reisseri , Chlorella vulgaris, and Chlorella variabilis. We did not confirm the occurrence of a division into American and European groups and we guess that this division is only contractual and corresponds to the amount of introns in the 18S rDNA, and that there is no strong correlation with the geographical location. We have demonstrated that the range of M. reisseri is greater than previously supposed. We identified algae strains originating from Southern Europe (Serbia), Western Asia, and from the Far East (Kamchatka) as M. reisseri. Moreover, we identified two strains originating from Europe as C. variabilis, which also contradicts the predetermes about a division into American and European groups.