INTEGRATION AND EXCISION OF PLASMID DNA IN LACTOCOCCUS-LACTIS SUBSP LACTIS

The capacity of the 75-kb lactose-proteinase plasmid pCI301 fromLactococcus lactis subsp.lactis UC317 to recombine with the lactococcal chromosome was examined. Low-frequency integration of pCI301 sequences was detected following protoplast transformation of strain MG1363Sm with total plasmid DNA from strain UC317. Excision of integrated sequences was subsequently observed at a low level. Excised sequences were rescued through recombination with and mobilization by the conjugative enterococcal plasmid pAMB1. Transconjugants harboring novel recombinant pCI301::pAMB1 plasmids, both pAMB1 and a pCI301 derivative, and pAMB1 only were isolated. The latter represents a class of transconjugant in which an elevated level of reintegration of pCI301 DNA in the recipient chromosome has occurred. © 1990 Academic Press, Inc. All rights reserved.