Paramecia that secrete into the medium particles that kill other paramecia. The killer trait is due to kappa particles, which reside in the cytoplasm of those strains of Paramecium aurelia syngen 2 that carry the dominant K gene. Later it was found that kappa particles were symbiotic bacteria and that the particles with killing activity were defective DNA phages. The lysogenic, symbiotic bacterium has been named Caenobacter taenospiralis, and it is but one of many kinds of bacterial endosymbionts that occur in over 50% of the P. aurelia collected in nature. See Chronology, 1938. Sonneborn; Paramecium aurelia.
Subjects: Genetics and Genomics.