Validation of the mutational spectra obtained with thelacZ Escherichia coli CLP and the Ames II Salmonella typhimurium strains

The six lacZ-- E.coli CLP strains (CL10XP; where X = 1--6) are each reverted by one of the six possible base substitutions. The relative responses of the six strains taken in parallel can be used to determine a compound's mutation spectrum. The responses of these strains to a set of mutagens of known mutational spectra and modes of action were tested. The predominant mutations caused by a set of seven diagnostic mutagens and the strains that scored these mutations were: 4-nitroquinoline 1-oxide, G → A (CL102P), G → C (CL103P) and G → T (CL104P); streptonigrin, A → C (CL101P), A → T (CL105P) and A → G (CL106P); N-methyl-N'-nitro- N-nitrosoguanidine G → T (CL102P); 5-azacytidine G C, (CL103P), N4-aminocytidine G → A, (CL102P) and A → G (CL106P) and N4-hydroxycytidine A → G (CL106P) . These responses were consistent with the results reported by Gee et al., (1994) using the Salmonella 700X (X = 1--6) bacterial test system. A further validation of the responses of the six CLP strains and the six Ames II strains was performed using six polycyclic aromatic hydrocarbon diol epoxide (PAHDE) isomers, the four stereoisomeric 1,2,3,4-tetrahydrobenzo[cjphenanthrene 3,4-diol 1,2-epoxides (BcPhDEs) and two of the stereoisomeric 7,8,9,10-tetrahydrobenzo[a]pyrene 7,8-diol 9,10-epoxides (BaPDEs) for which published mutational spectra exist. Comparisons of the bacterial mutational spectra with the published mutational spectra for the PAHDEs indicate that the E. coli strain CL103P scores G → C mutations consistently lower than published values, and the E. coli strain CL106P (A → G) may be a potential low scoring strain. In the Ames II Salmonella typhimurium TA 70OX system, a high scoring strain is TA 7004 (G → A), which often scores higher than published values. The S. typhimurium AT strains (TA 7001-- 7003) often scored a lower percentage of mutations. The low responses may be due to the excess response of some of the GC strains, particularly TA 7004.