Effects of amount and type of agar on the number of spontaneous revertants in the Ames test

It has been shown that the spontaneous revertants in the Ames test can depend on the amount and type of bottom agar on the plates. The most clear-cut effect was found with the his G46 strains, carrying the delta uvrB mutation, and with the new hisG428 strain, TA102. Evidence of mutagenic impurities in agar has been found.