Mutation and DNA modification in Salmonella exposed to N-nitrosodimethylamine under UVA- and sunlight-irradiation.

Previously, we reported that when Salmonella typhimurium and Escherichia coli were treated with N-nitrosodimethylamine (NDMA) under irradiation with ultraviolet-A (UVA), mutagenesis of the bacteria took place without externally added activation enzymes. We also observed the formation of O(6)-methylguanine (O(6)-meG), N(7)-methylguanine (N(7)-meG) and 7,8-dihydro-8-oxodeoxyguanosine (8-oxodG) in calf thymus DNA treated with NDMA plus UVA. In this study, we observed the mutagenicity of NDMA under irradiation of natural sunlight in S. typhimurium. Furthermore, we detected the formation of O(6)-meG, N(7)-meG and 8-oxodG in calf thymus DNA treated with NDMA plus simulated sunlight. Regarding the mutagenesis of S. typhimurium by NDMA plus UVA, we have now identified and quantified O(6)-meG formed in the genomic DNA of the bacteria under conditions of the mutagenesis.