Question

how do you know if a bacteria is a revertant

Answer 1

A revertant bacteria is the bacteria that has reverted back to the wild form from the mutated form. Revertant bacteria can be identified by Ames test. In the Ames test, bacteria that are auxotrophic and require histidine amino acid for their growth are treated with the test chemical, or vehicle, or positive control on an agar plate containing media that lacks the amino acid histidine. Only those bacteria that are reverted back can grow in the agar plates that lack histidine.