MODIFIED METHOD OF DETERMINING MIUTATION RATES IN BACTERIA'

The elucidation of many biological and meta-bolic processes has been facilitated by the use of microbial mutants. Studies concerning the ef-fects of radiations, the relation between killing and mutations, and the effects of different muta-genic agents on genetic material have been made with the prospect of correlating this information with that of more complex multicellular or-ganisms. In studies of this type it is desirable that the method employed for measuring induced mutations be simple yet reliable. MIethods devised for measuring in(luced muta-tion rates have as a basis the fluctuation test (Luria and Delbruck, 1943), the average number of mutants per culture in a series of parallel cul-tures (Newcombe, 1948), clonal systems and population dynamics (Lea and Coulson, 1949), and serial dilution methods (Pratt et al., 1954). It is the purpose of this paper to report a method for measuring induced mutationis which will eliminate many of the time consuming processes employed in some of the above methods, allow complete phenotypic expression and recovery of induced mutants, permit the assay of large populations, and measure many different types of mutations by use of the appropriate selective media. The method was used to compare the mutagenic action of ultraviolet irradiation and manganous chloride on the Y-53 strain of Escherichia coli strain K-12 and a threonine dependent strain (Texas) of E. coli strain B. 1 This work was supported by a grant-in-aid from the American Cancer Society upon recom-mendation of the Committee on Growth of th