Mutation spectra of chemical mutagens determined by Lac(+) reversion assaywith Escherichia coli WP3101P-WP3106P tester strains

We previously reported the development of mutation-specific Escherichia col i B tester strains WP3101 to WP3106 from strain WP2uvrA. In this study we c onstructed their pKM101-containing derivatives WP3101P to WP3106P, and furt her isolated their rfa derivatives WP4101-WP4106 and WP4101P-WP4106P. The s ix kinds of F' plasmids (lacI(-), lacZ(-), proAB(+)), each of which carries a different lacZ allele, contained in the above strains were originally de rived from E. coli K-12 strains CC101-CC106. All the tester strains show La c(-) and Trp(-) phenotype. Assays for transitions and transversions are bas ed upon Laci reversion of a specific mutation located within the lacZ gene on an F' plasmid. The trpE65(ochre) allele in the same strains enables them to be used for Trp(+) reversion assays as well. In the present paper, we e valuated the sensitivity, specificity, and usefulness of the newly develope d tester strains. Strains WP3101P-WP3106P were highly sensitive to determin e mutational profile of heterocyclic amines with S9 mix-mediated metabolic activation and most of the oxidative mutagens and free radical generators t ested. Every type of base-pair substitutions induced by 2-amino-3,4-dimethy limidazo[4,5-f]quinoline (MeIQ) or 5-diazouracil were detected in strains W P3101P-WP3106P, while A:T --> C:G and G:C --> A:T mutations induced by MeIQ , and A:T --> C:G, G:C --> A:T, and G:C --> C:G by 5-diazouracil were not d etected in pKM101-free tester strains. In pKM101-carrying strains, cumene h ydroperoxide induced all types of base substitutions, while formaldehyde pr eferentially induced G:C --> T:A transversions. Phenazine methosulfate indu ced predominantly G:C --> A:T transitions and G:C --> T:A transversions, wh ile H2O2 induced predominantly G:C --> T:A and A:T --> T:A transversions. I ntroduction of the rfa mutation considerably enhanced sensitivity to bulky mutagens such as polycyclic aromatic compounds. Air six possible base subst itutions induced by 9,10-dimethyl-1,2-benzanthracene (DMBA) were detected i n tester strains WP4101P-WP4106P. In conclusion, our tester strains WP3101P -WP3106P and WP4101P-WP4106P permitted rapid and simple detection of specif ic mutations induced by variety of mutagens. (C) 1999 Elsevier Science B.V. All rights reserved.