High-frequency conjugal transfer of a gonococcal penicillinase plasmid

Gonococci containing a 24 X 10(6)-dalton conjugal plasmid were able to mobilize for transfer a smaller, non-self-transmissible penicillinase (Pcr) plasmid with high frequency under appropriate conditions. In some strains, over 10% of donor colony-forming units transferred the Pcr plasmid in a mating of less than 2 h, which suggests that the conjugal system was naturally derepressed. Colony-opacity variants containing different quantities of an approximately 28,000-dalton outer membrane protein were altered in their ability to act as conjugal donors and recipients. Maximal transfer of the Pcr plasmid was observed between transparent donors and recipients, lacking appreciable amounts of the 28,000-dalton protein. Under conditions of high-frequency Pcr plasmid mobilization, no conjugal mobilization of chromosomal markers could be discerned.