Suppression of the thermosensitive replication phenotype of the derivative plasmid of pI9789::Tn552 in Staphylococcus aureus may involve integration of the plasmid into the host chromosome

Abstract

Plasmid-chromosome co-integration was found to be the mechanism of choice to overcome thermosensitivity of replication of the plasmid pS1 in PS80d and RN4220 strains of Staphylococcus aureus. The integration of the plasmid was sometimes accompanied by deletion of a specific section of the plasmid pS1 in PS80d. Growth of bacteriophage on strains containing the integrated plasmid and the subsequent use of the phage in transduction gave transductants containing plasmids that had regained their replication thermosensitivity. These plasmids had not acquired any detectable chromosomal DNA. The 16-kb EcoRI fragment of the PS80d chromosome that hybridizes to pS1 is the target for recombination in many cases, but apparently other sites are also used. This fragment contains sequence homologous to parts of the transposon Tn552 and it is probable that site-specific recombination is involved in the integration. The possible mechanisms for the integrations and the deletions are discussed.