Transduction of resistance determinants and R factors of the transfer systems by phage Plkc.

Abstract

Transduction by P1ke shows that Δ-mediated R factors fall into two groups: those in which the resistance and the Δ transfer factor are transduced as a single unit; and those in which the resistance determinant is transduced independently of the transfer factor. The first group is exemplified by the T-Δ R factor, which is transferable after transduction. An example of the second group is the SSu,Δ R factor, in which the SSu determinant is transduced independently to recipient cells. The SSu resistance is therefore not transferable until Δ is introduced into these recipients. These observations support the postulate, originally based on conjugational observations, that R factors are of two classes. In Class 1 the resistance determinant and the transfer factor form a single covalently bonded complex which is transferred intact to recipient cells; T-Δ belongs to this class. In Class 2 the resistance determinant and the transfer factor are separate plasmids. Although the transfer factor is necessary for transfer of the determinant in this class, independence of the plasmids is maintained in new hosts, and the nature of the association between the respective plasmids during transfer requires clarification.