Isolation of a Mutant of Salmonella Typhimurium Strain TA1535 with Decreased Levels of Glutathione (GSH-). Primary Characterization and Chemical Mutagenesis Studies

A mutant of Salmonella typhimurium strain TA1535 with decreased glutathione (GSH) levels was isolated after treatment with UV and selection for N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) resistance; this GSH- mutant also exhibited increased resistance to MNNG, the methyl analog of ENNG. Estimation of the cellular GSH content showed that the GSH- derivative contained about 20% of the GSH levels found in TA1535. In mutagenicity tests (hisG46 leads to His+), the GSH- strain required the presence of GSH or L-cysteine in the medium for an optimal phenotypic expression and/or growth of spontaneous and induced His+ revertants, and may, therefore, be allelic to cys mutants of Salmonella described earlier. The mutagenic activity of MNNG, ENNG and 1,2-dibromoethane (DBE), but not that of N-ethylnitrosourea (ENU), was strongly reduced in TA1535/GSH-; pretreatment of the strain with GSH restored the mutagenicity of the first 3 chemicals to levels normally found in TA1535. The results support the current view that MNNG, ENNG and DBE, but not ENU, can be activated via reaction with GSH to species of higher reactivity and mutagenicity. It is concluded that the present GSH- strain can be used to study more systematically the role of GSH in the bioactivation and -deactivation of xenobiotics to mutagenic factors.