Extrachromosomal Elements of Extrachromosomal Elements of Paramecium and Their Extrachromosomal Elements

Publisher Website
Google Scholar
Abstract
Members of the bacterial genus Caedibacter (commonly known as kappa particles) are obligate endosymbionts of paramecia. They confer killer traits upon their ciliate hosts, and, if one uses the term loosely, these bacteria can be considered to be extrachromosomal elements of killer paramecia. In fact, Caedibacter members were originally characterized as cytoplasmic genetic elements by T.M. Sonneborn in 1943 (21). In the belief that these bacteria were cytoplasmic genes, Sonneborn designated them as kappa in keeping with the convention at that time for naming cytoplasmic genetic elements. Sonneborn’s work on kappa is considered to be classic and had considerable impact on the development of modern biology, since it influenced researchers to consider the possible existence of extrachromosomal genetic elements in other biological systems. Subsequent cytological and genetic analyses of killer paramecia demonstrated the bacterial nature of kappa particles which now comprise the genus Caedibacter (6,7,9,10,13).