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 his⁻ 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.

Question

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 his⁻ 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.

Is the test compound still considered to be a potential mutagen? Explain why or why not.

Accepted Answer

Hi, everybody. Let's look at our next problem. It says, how does the Ames test evaluate the DNA Muto GIC of a substance in salmonella bacteria, particularly by using his minus string when the test compound is a pro mutagen that requires metabolic activation to become mugen. So before we walk through our answer choices and read them all, let's just briefly think through what goes on in the Aimes test in the Ames test. We start with his minus mutants of our salmonella bacteria and we recall that therefore, they will not grow in a medium lacking histidine. You then expose them to the potential mutagen, which if it has Mugen activity will cause some of those his minus mutants to sort of revert to be mutated back to his plus mutants. So if Muto GIC, some his plus mutants will arise. So you're sort of back mutating those mutants will be able to grow in medium lacking histamine. So colonies that grow, you will know were mutated by the test compound. And therefore that will show that it's muto there's one last little twist which as our question says, if the test compound is a pro Mugen, that requires metabolic activation. There are quite a number of mutagens that are not harmful just in and of themselves. But when they get processed through the liver become activated and have those mugen and capabilities. So, metabolic activation in this context would mean processed by the liver. So how would we sort of um replicate that in our test conditions? And the answer is when we want to look at compounds that might require this metabolic activation. We use S nine extract which contains liver enzymes. So those enzymes will be able to carry out the reactions they would in the liver and activate those mutagens. So with that in mind, thinking about the Ames test, let's read our answer choices and find the one that describes how the Aimes test then will evaluate the muto of a substance when it needs metabolic activation to become muto choice A says S nine extract and the test compound together produce high his plus reverence. While the test compound alone with the strain does not increase his plus reverence. Well, this is correct. You use the S nine extract to mimic that metabolic activation. If the S nine extract with the test compound produce a high number of those colonies that can now make their own histidine compared to just the test compound by itself. You know that that test compound is muto GIC only after metabolic activation. Choice B says the test compound alone with the strain produces high his plus reverence while adding S nine extract does not increase his plus reverence. Well, this would not show mutagens when the compound requires metabolic activation. Because in this case, the test compound didn't need the S nine extract to produce a high number of reverent. So that's why choice B is not our answer. Then choi says both the test compound alone with a strain and S nine extract and the test compound together generate high his fluster vergence. Well, if we don't see a difference, when we add the S nine extract, then we're not seeing that our strain needs that our mutagen excuse me needs metabolic activation. So choice C is not correct. And then finally, the test compound has no muto genetic potential regardless of metabolic activation high. His plus reverences are observed. Well, this is not correct because if the test compound is not muto GIC, then you will see no or almost no his plus for Vergence because you don't have anything to mutate them back. So choice D is not correct either. So again, our answer to how the Aimes test evaluates DNA Mugen when that test compound is a pro muto that requires metabolic activation to become muto choice A S nine extract and a test compound together produce high his plus reverence. While the test compound alone with the strain does not increase his plus reverence. See you in the next video.

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Key Concepts

Ames Test

S9 Extract

Mutagenicity