Isolation of Mutants with Altered DNA Base Composition in Bacillus subtilis 168

Abstract

WEED¹ exposed Bacillus subtilis strain 168 to copper sulphate at 43° C and induced a mutant with small colonies (sc-22) and altered DNA base composition, Gause et al.^2,3 induced other somewhat similar mutants in this strain by exposing it to 5-fluorouracil. In these experiments the parent culture was cultivated at 43° C for 3 days in nutrient broth containing 1 per cent of glucose and 100–250 µg/ml. of 5-fluorouracil. Twenty tubes were usually prepared for each concentration of 5-fluorouracil. When samples from these tubes were plated on nutrient agar containing 1 per cent glucose and then incubated at 37° C, mutants with small colonies were isolated. The DNA base composition in most of these mutants does not differ from that of the parent culture, B. subtilis 168. Mutation with altered DNA base composition represents an extremely rare event, and this communication describes a technique which can be used to detect these mutants.