Dominance of the Inducible State in Strains of Staphylococcus aureus Containing Two Distinct Penicillinase Plasmids

Abstract

Richmond, Mark H. (National Institute for Medical Research, Mill Hill, London, England). Dominance of the inducible state in strains of Staphylococcus aureus containing two distinct penicillinase plasmids. J. Bacteriol. 90: 370–374. 1965.—The phenotypic expression of penicillinase synthesis is studied in a strain of S. aureus containing two distinct plasmids, each carrying the penicillinase structural gene and its associated control (inducibility) gene. One plasmid in the heterodiploid carries the genes responsible for the normal, fully inducible synthesis of a structural mutant of type A penicillinase, and the second plasmid carries the genes required for constitutive synthesis of C-type enzyme. The heterodiploid is phenotypically fully inducible, indicating that the inducible state dominates the constitutive in penicillinase synthesis. The heterodiploid synthesizes approximately equal quantities of A- and C-type enzyme when fully induced. Parental types are obtained from the heterodiploid by spontaneous segregation at a frequency of about 1 per 1,000 divisions of each character. Recombination between the two plasmids in such a persistent heterodiploid is a rare event.