A comparison of mutation spectra detected by the Escherichia coli Lac+ reversion assay and the Salmonella typhimurium His+ reversion assay

Each of the Escherichia coli tester strains in the WP3101P–WP3106P series contains an F′ plasmid with a different base substitution mutation within the lacZ gene. Each of the six possible base substitution mutations, therefore, can be assayed with these strains by Lac+ reversion. We used the strains to characterize the mutational profiles of 21 chemical mutagens, including alkylating agents, base analogs and oxidative compounds. We also assayed the mutagens with Salmonella typhimurium tester strains TA7002, TA7004 and TA7005, which detect A˙T→T˙A, G˙C→A˙T and G˙C→T˙A mutations, respectively, and we compared the sensitivity and specificity of the two systems. Escherichia coli strain WP3102P was more sensitive than the S.typhimurium strains to G˙C→A˙T transitions induced by N4-aminocytidine, 5-azacytidine, cumene hydroperoxide (CHP), t-butyl hydroperoxide (BHP), N-ethyl-N′-nitro-N-nitrosoguanidine (ENNG), methyl methane sulfonate and N-ethyl-N-nitrosourea (ENU), while the reverse was true for G˙C→A˙T transitions induced by 2-aminopurine and phosmet. Escherichia coli strain WP3104P, which detects G˙C→T˙A transversions, was superior to the S.typhimurium strains in detecting transversions induced by N4-aminocytidine, 5-azacytidine, 5-diazouracil, CHP, BHP, ENNG, ENU, 4-nitroquinoline 1-oxide (4-NQO) and 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Escherichia coli WP3105P was also more sensitive than S.typhimurium to A˙T→T˙A transversions induced by N-methyl-N- nitrosourea (MNU), CHP and 4-NQO, but it was less sensitive to those induced by ENNG, ENU and 2-aminopurine. The present results indicate that the E.coli Lac+ reversion system with tester strains WP3101P–WP3106P is as sensitive as the S.typhimurium His+ reversion system for the detection of specific mutations induced by a variety of direct mutagens.