In an Ames test using his⁻ Salmonella bacteria a researcher determines that adding a test compound plus the S9 extract produces a large number of his⁺ revertants but mixing the strain plus the test compound without adding S9 does not produce an elevated number of his⁺ revertants. Is the test compound still considered to be a potential mutagen? Explain why or why not.

Key Concepts

Ames Test

The Ames test is a widely used assay to assess the mutagenic potential of chemical compounds. It utilizes strains of bacteria, typically Salmonella, that are unable to synthesize histidine (his⁻). If a compound induces mutations that restore the ability to synthesize histidine (resulting in his⁺ revertants), it suggests that the compound may be a mutagen.

S9 Extract

S9 extract is a metabolic activation system derived from the liver of rodents, containing enzymes that can convert pro-mutagens into their active mutagenic forms. In the context of the Ames test, the presence of S9 is crucial for evaluating compounds that require metabolic activation to exhibit mutagenic effects. The difference in revertant numbers with and without S9 indicates the necessity of metabolic conversion for the test compound's mutagenicity.

Mutagenicity

Mutagenicity refers to the capacity of a substance to induce genetic mutations, which can lead to cancer and other genetic disorders. A compound is considered a potential mutagen if it causes an increase in the frequency of mutations in a test organism. In the context of the Ames test, the presence of revertants in the S9 condition suggests that the compound may be mutagenic, while the absence of revertants without S9 indicates that metabolic activation is required for mutagenic activity.