The Rôle of Mutation and of Selection in the Frequency of Mutants Among Microörganisms Grown on Irradiated Substrate

Abstract

If selection is to explain the increased occurrence of mutants when Staphylo-coccus aureus is grown in irradiated broth, the following conditions should be met: (l)Quantitative expts. should show the mutants have a selective advantage over the normal strain under these conditions. This should be especially evident in a mixed culture. (2) When organisms are centrifuged from irradiated broth after a short exposure period and inoculated with unirradiated broth, the increase in the number of mutants should cease. (3) Both forward and reverse mutations should not be differentially increased by growth in irradiated broth. The results of the expts. reported do not fulfill any of these conditions but are in agreement with the hypothesis that mutations are induced by some factor in the irradiated broth.