A differential killing assay for mutagens and carcinogens based on an improved repair-deficient strain of Escherichia coli

Abstract

The lexA gene suppresses the spontaneous inviability of recA strains of E. coli without affecting their repair deficiency. This phenomenon was used to construct a uvrA recA lexA triple mutant CM871 that combines extreme repair deficiency with near wild-type growth. This strain was used in conjunction with an isogenic strain WP67 uvrA polA and isogenic wild-type strain WP2 in a differential killing test. Dilute suspensions in buffer of the repair-deficient strains and repair-proficient control are incubated for 2 h at 37.degree. C with test compound in the presence or absence of a S9 metabolizing system. Survival is determined by Miles Misra plating. For each strain three 10 .mu.l spots of each of 3 concentrations of test compound and of the untreated control are placed on a nutrient agar plate. Following overnight incubation survivors are counted. Results with reference compounds are given and the advantages and disadvantages of the test are discussed.