Conjugation and meiosis of Paramecium caudatum infected with the micronucleus-specific bacterium Holospora elegans.

Abstract

Cells of two complementary mating types of Paramecium caudatum, syngen 3, are infected with the micronucleus-specific bacterium Holospora elegans. Cells with bacteria in their micronuclei show the mating reaction with agglutination and pair formation. All the stages of meiosis in this species are observed and pronuclei are formed. During the pregamic divisions the bacteria are distributed to the division products, but many of the bacteria remain within the separation spindles, later being released into the medium. Therefore, the pronuclei contain only a few or no bacteria. In a test of the viability of exconjugant clones CNR-mutant (a behavioral mutant) and wild type cells, both infected with H. elegans, are crossed. The survival of exconjugants is very low (10.6% compared to 57.3% in the control). After conjugation only parental types are found indicating the occurrence of macronuclear regeneration after conjugation. The same result is obtained with cells which had contained bacteria but were cured by means of antibiotics. It is concluded that infected micronuclei have become genetically defective and did not give rise of new functional macronuclei. Therefore, H. elegans-bearing paramecia are genetically dead, which shows the parasitic nature of the bacterium H. elegans.