High copy number plasmid vectors for use in lactic streptococci

A 3.8 kb DNA fragment from plasmid pBD64 which encoded chloramphenicol and kanamycin resistance genes, but had no replication region, was used as a replicator probe to select for the replication region of the cryptic lactic streptococcal plasmid pSH71 using Bacillus subtilis as host. Three of the resultant recombinant plasmids, pCK1, pCK17 and pCK21 are described. They are vectors in Streptococcus lactis and can be used to clone BglII-compatible fragments into their kanamycin resistance gene. All the plasmids have single sites for restriction endonucleases AvaI, BamHI, EcoRI, PvuII and XbaI, while plasmids pCK17 and pCK21 have single sites for ClaI.