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)
Is it possible that Y contains a plasmid, whereas Y+ a transposon? When the Y+ transposon moves to Z, it locates at a different site?
The results can be explained by the concept of horizontal gene transfer, specifically through a process called conjugation.
Conjugation is a method of genetic transfer where genetic material, such as plasmids, can be passed between bacterial cells. It involves the formation of a physical bridge, called a pilus, between two bacterial cells, through which genetic material can be transferred from one cell to another.
In the first scenario, Bacteria Y, with the mutation at gene R that provides resistance to neomycin, transfers the genetic material containing this resistance to Bacteria Z. As a result, Bacteria Z acquires neomycin resistance. This transfer occurs because the mutated gene R in Bacteria Y is present on a plasmid that can be transferred to Bacteria Z during conjugation.
In the second scenario, when Bacteria Y+ (with the additional mutation at gene R providing resistance to streptomycin) is mixed with Bacteria Z, Bacteria Z does not acquire resistance to neomycin or streptomycin. This suggests that the additional mutation in Bacteria Y+ has altered the plasmid or the specific mechanism by which resistance is transferred.
To summarize, the explanation for these results is that the transfer of the mutated gene R, responsible for neomycin resistance, occurs through conjugation, a process of horizontal gene transfer between bacteria. The presence of an additional mutation in Bacteria Y+ affects the transfer of genetic material, preventing Bacteria Z from gaining resistance to neomycin and streptomycin.