Fusion and compatibility of camphor and octane plasmids in Pseudomonas

The octane (OCT) plasmid in Pseudomonas putida derived from the omega-hydroxylase-carrying strain of Coon and coworkers is transferable to the camphor (CAM) plasmid-bearing strain by conjugation or by transduction. While the majority of the Cam (+)Oct(+) exconjugants segregate Cam(+) or Oct(+) cells, exconjugants with stable Cam (+)Oct(+) phenotype (CAM-OCT) can be detected at a low frequency. The transductants are all of the CAM-OCT phenotype. In the stable Cam (+)Oct(+) strains, the OCT plasmid resembles the CAM plasmid with respect to curing by mitomycin C, transfer in conjugation, and reaction to ts (temperature-sensitive) mutation specifically affecting CAM plasmid replication. Therefore, it is suggested that certain regions of homology exist between the CAM and OCT plasmids that enable them to recombine to form a single plasmid, and to overcome the incompatibility barrier that prevents their coexisting.