An Hfr strain with the genotype cys⁺ lue⁺ met⁺ strˢ is m...

Question

An Hfr strain with the genotype cys⁺ lue⁺ met⁺ strˢ is mated with an strain carrying the genotype cys⁻ lue⁻ met⁻ strᴿ. In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:

Medium 1: Minimal medium plus leucine, methionine, and streptomycin
Medium 2: Minimal medium plus cysteine, methionine, and streptomycin
Medium 3: Minimal medium plus cysteine, leucine, and streptomycin

List all possible bacterial genotypes growing on each medium.

Accepted Answer

Hello, everyone. Let's look at our next problem. In a bacterial conjugation experiment. A researcher wanted to investigate the transfer of a plasmid containing a resistance gene from a donor strain to a recipient strain. The donor strain was resistant to ampicillin and carried the plasmid while the recipient strain was sensitive to ampicillin and lack the plasmid. The researchers used a selective medium that contained ampicillin to identify the trans conjugates after the conjugation after incubation, the researcher observed the growth of colonies on the selective medium. The results showed the presence of trans conjugate colonies on the selective medium. The researcher then picked 10 random trans conjugate colonies and tested them for Amin resistance. nine of the colonies were resistant to ampicillin while one colony was sensitive to ampicillin. What conclusion can the researcher make about the transfer of the plasmid and the resistance gene from the donor strain to the recipients strain? And our answer choices are a, the resistance gene has been destroyed. B the resistance gene was not successfully transferred. C the resistance gene has been successfully transferred to the recipient strain or D. The information is insufficient to make a conclusion. Well, we have this plate containing ampicillin and our recipient strain that used to not be used to be sensitive to amici now is able to grow on a plate with ampicillin. So that would lead us to believe that the colonies that have grown do contain that resistant gene. And the researchers saw by testing them that nine out of 10 colonies were resistant. So what is the conclusion here? Well, a is the resistance gene has been destroyed, But that does not make sense is our answer since we have nine colonies out of 10. So 90% that went from sensitive to resistant. So that definitely doesn't lead us to the conclusion that they've been, it's been destroyed. Choice B says the resistance gene was not successfully transferred Again. That would not be the conclusion you'd draw here. Um otherwise you wouldn't see 90% of your colonies with resistance. Choi C says the resistance gene has been successfully transferred to the recipients gene and this would be our likely conclusion. 90% of our colonies are now resistant. You still have that one out of 10 and that could be a result of incomplete transfer or loss of the plasmid um as the colony is growing, but you do have 90% that are resistant. And finally, choice D says the information is insufficient To make a conclusion, but 90% is pretty sufficient in concluding that the, the transfer has been successful. So choice d would not be our answer. So what conclusion can the researcher make about the transfer of the plasmid and the resistance gene from the donor strain to the recipient strain? Choice C the resistance gene has been successfully transferred to the recipient strain. See you in the next video.

Key Concepts

Hfr Strains and Conjugation

Interrupted Mating Experiment

Selection Media

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