Bacteria Y has a mutation within it’s genome, at gene R, that provides resistance to neomycin. Bacteria Z is sensitive to neomycin, however, when Bacteria Y is placed in a mixture with Bacteria Z, Bacteria Z also gains neomycin resistance.
One cell of Bacterium Y undergoes another mutation at gene R which now provides resistance to neomycin and a closely related anti-biotic, streptomycin. Bacteria Y that has the mutated R gene that gives resistance to both neomycin and streptomycin will be called Y+. When Bacteria Y+ is placed in a mixture with Bacteria Z (that has never been exposed to Bacteria Y before), Bacteria Z does not gain neomycin or streptomycin resistance.
What can explain these results?
So basically:
Bacteria Y (res to neo) + Bacteria Z (sens to neo) = Bacteria Z (res to neo)
Bacteria Y+(res to neo & strep) + Bacteria Z(sens to neo)=Bacteria Z(sens to neo)
A microbiologist inoculates a growth medium with 150 bacterial cells/ml. If the generation time of the species is 3 hours,
(a) how many generations will it take for the culture to contain more than 9,500 cells/ml? (5 pts.)
(b) how long, in hours, will it be before the culture contains more than 9,500 cells/ml? Show your calculations. (5 pts.) (Points : 10)
A) 3
B) 9
The results can be explained by the phenomenon of horizontal gene transfer, specifically through a process called conjugation.
Conjugation is a mechanism of genetic exchange in which genetic material, such as plasmids or segments of DNA, can be transferred from one bacterium to another. In this case, Bacteria Y, which has a mutation in gene R providing resistance to neomycin, can transfer this resistance to Bacteria Z.
When Bacteria Y undergoes another mutation in the same gene R, resulting in resistance to both neomycin and streptomycin, the bacterium is called Y+. However, when Bacteria Y+ is introduced into a mixture with Bacteria Z, Bacteria Z does not gain resistance to either neomycin or streptomycin.
This lack of transfer of resistance can be attributed to several possible explanations:
1. Specificity of plasmids: The resistance genes for neomycin and streptomycin may be present on different plasmids, and only the plasmid carrying the neomycin resistance gene is transferring to Bacteria Z. Therefore, Bacteria Y+ does not transfer the plasmid carrying the streptomycin resistance gene to Bacteria Z.
2. Lack of plasmid uptake: Bacteria Z may not possess the necessary receptors or mechanisms to take up the plasmids containing the streptomycin resistance gene. Without the ability to uptake the plasmid, the resistance gene cannot be transferred, resulting in Bacteria Z remaining sensitive to both neomycin and streptomycin.
3. Incompatibility of plasmids: The plasmid carrying the streptomycin resistance gene in Bacteria Y+ may be incompatible with Bacteria Z. Incompatibility can arise due to differences in replication or regulation mechanisms between the plasmids carried by the two bacterial strains. As a result, the plasmid carrying the streptomycin resistance gene is unable to function properly in Bacteria Z.
These explanations highlight the complex nature of gene transfer mechanisms and the specific interactions required for successful horizontal gene transfer.