Genetic Relationships among Bacterial Endosymbionts of Paramecium aurelia: Deoxyribonucleotide Sequence Relationships among Members of Caedobacter

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Abstract
Genetic relationships among bacterial endosymbionts of Paramecium assigned to the genus Caedobacter Preer et al. 1974 were determined using DNA-DNA hybridization techniques. It was shown that mu, nu and pi endosymbionts are closely related to each other, but not to any of the strains of kappa endosymbionts tested, and that kappa consists of at least three distinct and genetically diverse groups. Therefore, it is proposed that Caedobacter be split into two genera, Caedobacter and Pseudocaedobacter, depending upon the ability or lack of ability, respectively, to produce cells containing R bodies. Strains were screened for covalently closed, circular DNA by ethidium bromide/CsCl centrifugation, but only pi and hump-killer kappa particles were found to contain this form of DNA.