Identification of Paramecium bursaria syngens through molecular markers--comparative analysis of three loci in the nuclear and mitochondrial DNA

This is the first attempt to resolve the phylogenetic relationship between different syngens of Paramecium bursaria and to investigate at a molecular level the intraspecific differentiation of strains originating from very distant geographical locations. Herein we introduce a new collection of five P. bursaria syngens maintained at St Petersburg State University, as the international collection of syngens was lost in the 1960s. To analyze the degree of speciation within Paramecium bursaria, we examined 26 strains belonging to five different syngens from distant and geographically isolated localities using rDNA (ITS1-5.8S-ITS2-5'LSU) fragments, mitochondrial cytochrome c oxidase subunit I (COI), and H4 gene fragments. It was shown that P. bursaria strains of the same syngens cluster together in all three inferred molecular phylogenies. The genetic diversity among the studied P. bursaria strains based on rDNA sequences was rather low. The COI divergence of Paramecium bursaria was also definitely lower than that observed in the Paramecium aurelia complex. The nucleotide sequences of the H4 gene analyzed in the present study indicate the extent of genetic differences between the syngens of Paramecium bursaria. Our study demonstrates the diagnostic value of molecular markers, which are important tools in the identification of Paramecium bursaria syngens.