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does sodium deoxycholate effect salmonella typhimurium

Genetics as it applies to evolution, molecular biology, and medical aspects.

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does sodium deoxycholate effect salmonella typhimurium

Postby amberdagp » Fri Dec 25, 2009 11:28 am

Hi there
I hope everyone is well
I really need help, I cant find the information I need..

Firstly, I know that crystal violet on filter paper, in the presence of wild type salmonella typhimurium strain creates inhibition around the filter paper, but also bacterial growth after and around the inhibition zone. Is this right?
Im not sure what happens to the bacterial growth when Sodium Deoxycholate is applied, does anyone know?

Furthermore, how do you find out the mutation rate of two given mutagens? i have also tried to such for this, but find this confused :S

Thank you for all your help in advance!!
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Postby JackBean » Fri Dec 25, 2009 11:46 am

Look for Ames test/assay. You get let's say His- bacteria and plate them on plates w/o His (so they can't grow), one plate free and one plate with your substance (you can use also several concentrations of course).
On the free plate you find out native revertants, that is, how many colonies mutate back without any help. On the plates with your mutagen you should have more colonies formed. The more colonies, the stronger mutagen it should be.
Anyway, mutagens can cause different mutations, whereas this test requires quite strict mutation, so the accuracy may not be perfect ;)
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Re:

Postby amberdagp » Fri Dec 25, 2009 12:12 pm

Thank you for your reply:) so what you are saying is that if the Salmonella typhimurium strain has a defective gene that cannot synthesise HIS, and the medium culture does NOT contain HIS then this mutation can be reversed, and so can grow back?

But if a mutagen is grown with the bacteria, for the bacteria to grow HIS should be present in the culture in order to form more colonies?


JackBean wrote:Look for Ames test/assay. You get let's say His- bacteria and plate them on plates w/o His (so they can't grow), one plate free and one plate with your substance (you can use also several concentrations of course).
On the free plate you find out native revertants, that is, how many colonies mutate back without any help. On the plates with your mutagen you should have more colonies formed. The more colonies, the stronger mutagen it should be.
Anyway, mutagens can cause different mutations, whereas this test requires quite strict mutation, so the accuracy may not be perfect ;)
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Postby JackBean » Fri Dec 25, 2009 7:54 pm

Well, His+ strain is histidine-autotroph, can produce His by itself. His- is histidine-heterotroph, for some reason needs histidine to be supplemented, so His- strain can't grow on medium w/o His. BUT - mutations sometimes occur (even w/o mutagens), so even on plate w/o mutagen can some (originally His-, now of course His+) bacteria grow ;)
And if you add some mutagen, the rate of mutagenesis should increase and that should lead to increased grow on such a plate ;)

Of course, if the mutagen will lead to some frame shifts, that probably won't cause reversion of His-, so you could not detect such a mutagen, but if it causes some exchanges, that could be fine ;)
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