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 c ontains an F' plasmid with a different base substitution mutation within th e lacZ gene. Each of the six possible base substitution mutations, therefor e, can be assayed with these strains by Lac(+) reversion. We used the strai ns to characterize the mutational profiles of 21 chemical mutagens, includi ng 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 t he S.typhimurium strains to G . C --> A . T transitions Induced by N-4-amin ocytidine, 5-azacytidine, cumene hydroperoxide (CHP), t-butyl hydroperoxide (BHP), N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), methyl methane sulfonat e and N-ethyl-N-nitrosourea (ENU), while the reverse was true for G . C --> A . T transitions induced by a-aminopurine and phosmet, Escherichia coli s train WP3104P, which detects G . C --> T . A transversions, was superior to the S.typhimurium strains in detecting transversions induced by N-4-aminoc ytidine, 5-azacytidine, 5-diazouracil, CHP, BHP, ENNG, ENU, 4-nitroquinolin e 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 t o A . T --> T . A transversions induced by N-methyl-N-nitrosourea (MNU), CH P and 4-NQO, but it was less sensitive to those induced by ENNG, ENU and 2- amino-purine, The present results indicate that the E.coli Lac(+) reversion system with tester strains WP3101P-WP3106P is as sensitive as the S.typhim urium His(+) reversion system for the detection of specific mutations induc ed by a variety of direct mutagens.