Testing of chemicals for inhibition of the killer action of Paramecium aurelia.

Nearly 100 chemicals, chiefly purincs and pyrimidines and a few antibiotics, have been tested for their ability to interfere with the killing action of Paramecia and to produce sensitives from killer animals, presumably through inactivation of kappa. Kappa, a cytoplasmic factor in certain stocks of Parumecium uureliu, dependent upon, but not initiated by, the dominant allele of the killer gene, is known to be involved in the production of the antibiotic paramecin (l-3). Sensitive stocks of Purum&u with the recessive killer gene, which therefore cannot maintain kappa, and those killer animals depleted of kappa are affected by paramecin and ultimately die in its presence (1). The advantages of using Protozoa as test animals in testing essential nutrients and their analogues for effects on sensitivity, locomotion, growth, reproduction, and survival have been emphasized previously (4, 5). Purume&u with kappa, an independently multiplying cytoplasmic entity containing desoxyribonucleic acid (6,7), appeared to offer a system for demonstrating possible selective interference with nucleic acid metabolism. Inactivation of kappa by high temperature (8), x-rays (9), nitrogen mustards (lo), streptomycin (11)) and Chloromycetin (12) has been reported previously. This paper reports a survey of compounds for possible ability to decrease the content of active kappa in Paramecia as detected by decreased killing ability. Observation of the detrimental effects of 2,6diaminopurine on the killing ability (13) encouraged inclusion in this study of many compounds which might be expected to influence nucleic acid metabolism.