title: Construction of isogenic gonococcal strains varying in the presence of a 4.2-kilobase cryptic plasmid.
abstract: A 4.2-kilobase (kb) cryptic plasmid is present in 96% of isolates of Neisseria gonorrhoeae. An inability to construct isogenic derivatives which vary in the presence of the 4.2-kb plasmid has prevented the study of its function. We report a method to deliver an intact 4.2-kb plasmid into plasmidless gonococcal strains. The method involved transformation with novel 15.7-kb hybrid penicillinase-producing (Pcr) plasmids, which were cointegrates containing two copies of the 4.2-kb plasmid arranged in tandem direct repeat plus one copy of the 7.2-kb Pcr plasmid pFA3. When the 15.7-kb hybrid Pcr plasmids were introduced into a gonococcal recipient lacking evident plasmids, they dissociated at a relatively high frequency into plasmids identical to their parents: the 4.2-kb cryptic plasmid and pFA10 (a stable 11.5-kb plasmid containing one copy of each of the 7.2-kb Pcr plasmid pFA3 and the 4.2-kb cryptic plasmid pFA1). Curing strains of their Pcr plasmids resulted in isogenic strains which varied only in the presence of the 4.2-kb plasmid. The presence of the autonomously replicating 4.2-kb plasmid did not affect a number of tested phenotypes, including auxotype, antibiotic sensitivity, and frequencies of variation of outer membrane protein II. The interpretation of the functional significance of the 4.2-kb plasmid was complicated, however, by the additional finding that each of three tested plasmid-free strains contained a chromosomal fragment of about 1.6 kb that hybridized under moderate stringency with a 1.65-kb HinfI fragment of the 4.2-kb plasmid.
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D005796:Genes; D005798:Genes, Bacterial; D005822:Genetic Vectors; D008970:Molecular Weight; D009344:Neisseria gonorrhoeae / Q000235:genetics*; D010957:Plasmids; D014170:Transformation, Genetic
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004269:DNA, Bacterial