Proteus mirabilis converting phage 5006Mpa has an oversized genome

Proteus mirabilis phage 5006Mpa is a converting variant for ampicillin resistance of phage 5006M. We show here that the ampicillin resistance marker of transposon Tn1 is located on a 9.8% insertion with respect to the wild-type phage genome. This renders the 5006Mpa genome 5% oversized, albeit without loss of wild-type genetic material from the phage population.