Thank you for your reply, Dr. Kim.

I am still confused about the first question. Both phages were induced from strain A, and yet one of which could lysis strain A and had plaque formation but the other couldn't in spot test. Could a specific immunity develop against a phage while it is integrated in the genomic DNA?

thanks

Hi,

II have suggestions,which may help, and a comment.

If your A strain is lysogenic (contains “prophage copies”) for the two phages you recovered after MytC induction, one would expect that strain A is “immune” for those phages because the prophages synthesize a repressor which blocks the lytic development of the superinfecting phages. As suggested by Shukho Kim this may be the case for one but not the other of your phage. This would be somewhat unexpected though. Generally a strain that carries a prophage is immune to the corresponding phage.

Another reason for a phage not to grow on a given strain (here A) after it has been propagated on another one (here B) may be the presence of different restriction-modification systems in strain A and B. One of your phage may be sensitive to the RM system(s) in A but not the other. But again I'd favor the immunity hypothesis.

Do yo have indications about the number of prophages present in strain A? One of the phages you get after induction may be a recombinant between for instance a cryptic prophage and a complete one. This should result in different bursts for the two phages. But there are for sure many other possibilities.

Your sentence “There is no antibiotic marker available on the phage, what is the best way to perform a phage transduction and select the lysogency clones?” is somewhat misleading. You seem to wish to isolate a lysogen but you mention a transduction. It is correct that specialized transduction, (of a marker flanking the prophage) usually produces transductants that are lysogenic. But all lysogens are not transductants. They just gain a propahge and no other marker from the former host used to grow the phage.

Normally if you spot a lysate of the phage (10E8-10E9) on a lawn of the strain you want to “lysogenize”, grow and recover colonies that have developed in the phage spot by streaking for isolated colonies, most of these should have a propahge and hence produce phage on a lawn of sensitive bacteria. This of course requires that the host you lysogenize does not already produce phages! A resistance marker helps for this but is surely not essential!

Hope this is of some help.