Question

Recall that in the Ames Test, potential mutagens are tested for their ability to revert His− auxotrophs to His+. Any particular his- mutation present in a His− auxotrophic bacterial strain would be able to be reverted only by some mutagens and not others. Yet, the purpose of the Ames Test is to determine whether or not a specific substance is a mutagen of any type. How is the Ames Test actually performed to circumvent this problem?

Answer 1

To work around this problem, the Ames test is done as follows:

A petri dish is seeded with salmonella colonies, moreover, in that petri dish a little chemical is added in the center. A culture medium is also added to the plate where agar is one of the ingredients and biotin and histidine have been mixed.

Only bacteria that show some kind of mutation will grow on these agar plates. This is because histidine has the function of allowing cell divisions necessary only for cases in which mutagenesis is necessary to occur.