[Mutagenicity of steviol: an analytical approach using the Southern blotting system].
Steviol is the aglycone of stevioside, which is a non-caloric sugar substitute commonly used in Japan. Our previous studies and Pezzuto et al. have demonstrated that steviol is mutagenic after metabolic activation in the forward mutation assay using Salmonella typhimurium TM677 (TM677), whereas it is non-mutagenic in the reverse mutation assay (Ames test) using S. typhimurium TA 100, TA98, TA102 and TA97. There is the possibility, therefore, that activated steviol selectively induces a deletion or insertion of more than one base pair which cannot be detected by strains commonly used in the Ames test. In this study, we confirmed first that the 8-azaguanine (8-AG) resistance of the TM677 mutants appears to reside in the chromosomal gpt gene, since it can be complemented by the gpt gene of E. coli (Ecogpt). The chromosomal DNA of TM677 and TM677 mutants were digested by several restriction enzymes: BamHI, Sau3AI, AluI, TaqI, HaeIII, HpaII and RsaI, and analyzed by the Southern blot hybridization technique with a probe to the gpt gene DNA of E. coli. No significant differences in DNA fragment length, however, were formed between the wild type and spontaneous or steviol-induced mutants.