Abstract
A recombination-deficient (rec-) strain, AB2463, of Escherichia coli K12 yielded λ lysogens of two types. A rare form, AB 2463 (λ)(ind), differed from the usual type, AB 2463 (λ), in showing ultraviolet (u.v.) irradiation induction of the prophage, forming normal numbers of conjugational recombinants and displaying a u.v. response curve similar to that of the parental rec+ strain, AB 1157. Superinfection of the inducible form with phage 21 b2 led either to loss of the prophage or to the infrequent production of a form which was still lysogenic but no longer inducible. In both cases the bacteria regained their rec- condition as a result of the curing treatment. The phage released from AB 2463 (λ)(ind) was normal λ. It is concluded that the rec+ phenotype of AB 2463 (λ)(ind) derives from the presence of the prophage and represents a case of host conversion. It is proposed that AB 2463 (λ)(ind) is doubly lysogenic for λ and that partial curing yields the rec- single lysogen AB 2463 (λ).
* Present address: New Zealand Dairy Research Institute, P.O. Box 1204, Palmerston North New Zealand.