IDENTIFICATION OF CISTRONS INVOLVED IN CONJUGAL TRANSFER OF NARROW HOST-RANGE R-PLASMID R91-5 OF PSEUDOMONAS-AERUGINOSA

The development of a transductional method for complementation tests between transfer-deficient mutants of the narrow-host-range R plasmid R91-5 of P. aeruginosa allowed the identification of cistrons involved in the conjugal transfer of this plasmid. Complementation tests performed between transfer-deficient mutants characterized phenotypically with respect to sensitivity to donor-specific phage, ability to inhibit the replication of phage G101 and expression of entry-exclusion has identified a minimum of 10 transfer cistrons. Although most mutagen-induced mutants were relatively heterogeneous and appeared to be affected in a single cistron only, a high proportion of mutants isolated after selection for donor-specific phage resistance had deletions, but always included traY. Mutants selected directly on the basis of transfer deficiency which also became donor-specific phage resistant fell into all 10 cistrons, suggesting that many R91-5 transfer cistrons are concerned with the synthesis of sex pili and other surface structures necessary for conjugal transfer. Conversely, most retaining donor-specific phage sensitivity belonged to 1 cistron, whereas transfer-deficient mutants which also lost the ability to inhibit the replication of phage G101 comprised 4 cistrons.