Strain-specificity of mutational types in the Ames Test

    Different strains of his^- Salmonella bacteria are used to test for different types of mutagenic activity. For example, Aflatoxin B₁ is a mycotoxin produced by fungal growth on a variety of crop plants. Besides being among the most potent toxins, Aflatoxin is also a mutagen that binds to G bases and induces apurinic sites in DNA. The TA100 and TA1538 are his^- Salmonella bacterial strains sensitive to reversion mutations by base substitutions and frameshifts, respectively. In the experiment above, increasing concentration of Aflatoxin induces larger numbers of substitution mutations in the TA100 strain [upper plot], but not frameshift mutations in the TA1538 strain [lower plot], as predicted.