Phenotypic Polymorphism in Two Endosymbiotic Bacteria of the Ciliate Paramecium: Pseudolyticum multiflagellatum and “Ca. Megaira venefica”

Here, we report a comprehensive description of the stable associations between two Paramecium species (P. nephridiatum and P. caudatum) their cytoplasmic bacterial endosymbiont Pseudolyticum multiflagellatum. These spindle-like, rod-shaped, non-motile peritrichous bacteria demonstrate significant phenotypic polymorphism. Considering differences in morphology host species, several scientific groups have previously described these endosymbionts as distinct species. Our study provides brand-new molecular data, which allows us to unify earlier descriptions determine phylogenetic position this member family “Ca. Midichloriaceae” (Rickettsiales). The distinguishing feature bacterium is presence highly refractive granule its cytoplasm, well detectable with differential interference contrast (DIC) microscopy. protein nature peculiar inclusion bodies considered. other endosymbiont, Megaira venefica”, co-inhabiting cytoplasm studied strains, also displayed polymorphism, rounded forms being infected phages.