New tester strains of Salmonella typhimurium lacking O6-methylguanine DNA methyltransferases and highly sensitive to mutagenic alkylating agents.

摘要

Salmonella typhimurium YG7104 and YG7108 are derivatives of the Ames tester strain TA1535, and have chromosomal deletions of the ogtST gene or both the ogtST and adaST genes, respectively. The ogtST and adaST genes encode O6-methylguanine DNA methyltransferases that are involved in the repair of DNA damage caused by alkylating agents. The sensitivities of these strains to 15 mutagens with different structures were tested and compared with those of the parent strain TA1535. Deletion of ogtST or ogtST plus adaST substantially increased the sensitivity of strain TA1535 to the mutagenicity of alkylating agents, such as N-ethyl-N'-nitro-N-nitrosoguanidine, ethyl methanesulfonate or dimethylnitrosamine (DMN). Preincubation of the chemical with S9 mix and bacteria for 20 min at 37 degrees C before pouring them together on agar plates was not necessary to detect the mutagenicity of DMN when strain YG7104 or YG7108 was used as a tester strain. Introduction of plasmid pKM101 did not enhance but rather decreased the sensitivity of YG7104 and YG7108 to alkylating agents. Since the new strains are highly sensitive only to alkylating agents, they will be useful to detect the mutagenicity with high efficiency and to study the mechanism of mutagenesis induced by environmental alkylating agents.