Characterization of pER371-based Streptococcus thermophilus Escherichia coli shuttle vectors

Native plasmid of Streptococcus thermophilus ST137, pER371 (2.7 kb) linearized at various unique restriction sites was individually subcloned into Escherichia coli plasmid pUC19 to generate the pUER-series recombinants. A selection cassette consisting of chloramphenicol- and erythromycin-resistance genes was spliced into each construct to generate the pMEU shuttle vectors. Electrotransformation of Streptococcus thermophilus with these vectors showed that a ca. 1.7 kb BstEII/BanII fragment is essential for plasmid replication. A shuttle vector, pMEU14'-1 (5.3 kb), was constructed using the minimally required fragment for replication. A chloramphenicol acetyltransferase (cat) gene was successfully expressed in the ultimate S. thermophilus host by using pMEU14'-1 Cloning vectors derived from pER371 should provide valuable alternative gene delivery vehicles for the genetic engineering of lactic acid bacteria.