ИСТИНА

Five microsporidian nucleotide sequences of the SSU rRNA gene were PCR amplified from DNA samples of gregarines parasitic in White Sea polychaetes. Three sequences were obtained from gregarine Ancora sagittata parasitic in the gut of Capitella capitata (two of them were almost identical and differed by only a few substitutions); and two more sequences were obtained from gregarines parasitic in Lumbrineris fragilis: one from Lecudina cf. elongata and another from L. cf. longissima. All the sequences formed a stable monophyletic clade (with a posterior probability of 0.99) at the base of a Bayesian tree of 70 microsporidian species, which represent all branches commonly resolved in the SSU rDNA phylogenetic analysis. Some representatives of the hyperparasitic microsporidian family Metchnikovellidae are morphologically described from gregarine hosts mentioned above or from their close relatives: two Amphiamblys species from Ancora sagittata and two Amphiacantha species from Lecudina spp. parasitic in Lumbrineris spp. (including L. elongata). Our previous light and electron microscopic studies on the gregarines, from which the microsporidian sequences were obtained, also often demonstrated vegetative stages of microsporidians and characteristic spore-containing cysts similar to those of Amphiamblys and Amphiacantha. This suggests that the obtained sequences belong to these microsporidians too. Thus, molecular phylogenetic analysis confirms the affiliation of Metchnikovellidae to microsporidians and demonstrates that they are the most plesiomorphic group of modern Microsporidia.