A Nonkiller Resistant Kappa and Its Bearing on the Interpretation of Kappa in Paramecium Aurelia.

IN spite of more than 20 years of investigation by many workers (reviewed by SONNEBORN 1959), kappa-the first-discovered cytoplasmic genetic basis of the killer trait in Paramecium aurelia-still poses intriguing problems. Among them are the correlation of kappa’s visibly distinguishable forms with its diverse properties: abilities to reproduce, to infect, to kill and to confer complete resistance against homologous killing kappa; the relation of these visible forms to a developmental series; and the peculiar mutational spectrum and sequences exhibited by kappa. The present study bears on all these problems by exploiting a killer mutant possessing properties unlike any heretofore known. The killer trait is recognized when paramecia (killers) containing cytoplasmic symbionts affect other paramecia (sensitives) lacking symbionts in visibly adverse ways and eventually cause them to die (SONNEBORN 1939; 1959). There are many kinds of killers, differing in the ways they affect sensitives, in the conditions for this action, and in the visible features of their determinative symbionts. These differences constitute the bases for assigning descriptive terms to the types of killers (hump, spinner, vacuolizer, paralyzer, rapid lysis and matekiller) and different designations (kappa, lambda, mu and sigma) to the various symbionts (SONNEBORN 1959). The following account relates primarily to hump kappa and hump killers which cause sensitives to form large posterior aboral humps before the onset of death. Killer paramecia act on sensitives by means of killing particles (formerly called paramecin particles) liberated into their medium. Killers are resistant to their own kind of killing particles but are sensitive to toxic particles liberated by paramecia affecting sensitives in other ways. Thus the kind of kappa present in a paramecium determines, except in cases of gene-determined syngenic insensitivity, its pattern of resistance and sensitivity as well as its kind of killing. The amount of kappa present also influences the phenotype. A progressive reduction in the amount of kappa per animal is accompanied by successive phenotypic changes from resistant killer, to resistant nonkiller, to reversible sensitive, to irreversible sensitive ( SONNEBORN 1946; PREER 1948). Kappa stain with Feulgen or Giemsa reagents after acid hydrolysis (PEER 1950). TWO visibly distinct forms are found when crushed unstained killers are