Isolation and Characterization of Macronuclei of Paramecium Caudatum Infected with the Macronucleus-specific Bacterum Holospora Obtusa

Endosymbiotic associations between bacteria and eukaryotes are commonly reported (Taylor, 1983). The prokaryotic cell (the cytobiont (Taylor, 1979) or endocytobiont (Schwemmler, 1979)) may live non-specifically within the intracellular habitat provided by the host, but some endosymbiotic bacteria are specialized to invade specific cellular organelles. Three species of the bacterial genus Holospora invade exclusively the nuclei of the ciliate Paramecium caudatum. Like other ciliates P. caudatum contains two different nuclei, the generative, transcriptionally inactive micronucleus and the vegetative, transcriptionally active macronucleus (for a review see Nanney, 1980). Both types of nuclei can be infected by some species of the genus Holospora. Whereas Holospora elegans and H. undulata can only be found in the micronucleus of P. caudatum, H. obtusa is restricted to the macronucleus (for a review see Gortz, 1983). In all Holospora species two morphologically different forms can be distinguished. The long infectious form is taken up from the surrounding medium into a food vacuole and then transported into the nucleus that is specific to the species. Having reached the nucleus the infectious form differentiates by multiple fissions into the smaller reproductive form, which multiplies by binary fission. From the reproductive form the infectious form can then be developed and released into the medium (Ossipov & Podlipaev, 1977; Gortz & Dieckmann, 1980). Normally, the endonuclear bacteria do not destroy the P. caudatum cell. They