Integration and excision of a plasmid inBacillus subtilis

摘要

We have studied the behaviour inBacillus subtilisof a plasmid (pPV21) carrying the thymidylate synthetase gene of phage ϕ3T (thyP3). The plasmid can transform efficiently the competent cells of all the strains tested. Polyethylene glycol (PEG)-mediated protoplast transformation is efficient only forrecE, recDorrecFmutants. When present in recombination proficient strains, the plasmid can be integrated into the chromosome, primarily at thethyAlocus. This has been shown by genetic mapping and by blot-hybridization. A second less efficient site is at (or near to) the attachment site of phage ϕ3T. Excision of the plasmid restores theEcoRI restriction pattern of the parental DNA, although with the loss of the defectivethyAendogenotic allele and the retention of thethyPexogenotic gen