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Methyl methanesulphonate (MMS) is clearly mutagenic in S. typhimurium strain TA1535; a comparison with strain TA100
E Eder1, C Deininger, M Wiedenmann
1Institute of Toxicology, University of Würzburg, F.R.G.
Abstract:
No mutagenicity or an uncertain mutagenic response has been reported in the literature for methyl methanesulphonate (MMS) in S. typhimurium strain TA1535 when using the plate assay. In our studies we found a reproducible mutagenic activity of 62 revertants/mumole and plate for MMS in strain TA1535 when using the preincubation assay. A dose-dependent increase in revertants was, however, observed only at fairly high doses (exceeding 4 mumole). Two different slopes were observed in the dose-response curve when testing MMS with strain TA100. Slope A is dependent on the error-prone response, possible only in strain TA100 due to the pKm101 plasmid (R factor) but not possible in strain TA1535 due to its umuDC deficiency. Slope B observed at higher doses (as in strain TA1535) could be explained through a GC----AT transition initiated by the O6-methylation of guanine. Our findings demonstrate that MMS induces back mutation in S. typhimurium strains carrying the hisG46 missense mutation due to the formation of O6-methylguanine. In the case of strain TA100 the pKm101 plasmid-mediated error-prone mechanism is, however, the predominant process in MMS mutagenesis which leads to a higher mutagenic response at much lower doses than the GT----AT transition in strain TA1535.
Insights
Methyl methanesulphonate (MMS) shows mutagenic activity in Salmonella typhimurium TA1535 via preincubation assays. This mutagenicity, primarily through O6-methylguanine, is more pronounced in TA100 strains due to error-prone repair mechanisms.
Area of Science:
- Toxicology
- Genetics
- Microbiology
Background:
- Methyl methanesulphonate (MMS) is a known alkylating agent.
- Previous studies reported uncertain mutagenicity of MMS in Salmonella typhimurium strain TA1535.
- The role of specific bacterial strains and assay methods in MMS mutagenicity requires further clarification.
Purpose of the Study:
- To investigate the mutagenic activity of MMS in Salmonella typhimurium strains TA1535 and TA100.
- To elucidate the mechanisms underlying MMS-induced mutagenesis.
- To compare the dose-response and mutagenic pathways of MMS in different bacterial strains.
Main Methods:
- Bacterial reverse mutation assays (plate assay and preincubation assay) were performed.
- Salmonella typhimurium strains TA1535 (umuDC deficient) and TA100 (pKm101 plasmid) were used.
- Dose-response curves were analyzed to determine mutagenic activity and mechanisms.
Main Results:
- Reproducible mutagenic activity of MMS was observed in strain TA1535 using the preincubation assay.
- A dose-dependent increase in revertants was noted at higher MMS doses in TA1535.
- Two distinct dose-response slopes were observed in strain TA100, indicating different mutagenic pathways.
Conclusions:
- MMS induces back mutations in S. typhimurium strains with the hisG46 missense mutation, primarily through O6-methylguanine formation.
- In strain TA100, the pKm101 plasmid-mediated error-prone mechanism is the predominant mutagenic pathway for MMS at lower doses.
- The umuDC-deficient strain TA1535 relies on GC----AT transitions at higher doses, suggesting strain-specific mutagenic responses to MMS.