DNA sequence analysis and Southern hybridizations, together with complementation experiments, were used to study relationships between lactococcal plasmid replicons. pWVO2, pWVO4 and pWVO5, which co-exist in Lactococcus lactis subsp. cremoris Wg2, and pIL7 (isolated from another strain) all contained a functional replication region which appeared to be very similar to that of some known lactococcal plasmids. They contain a gene encoding a highly conserved RepB protein (60–80% amino acid identity between pWVO2, pWVO4 and pWVO5), which is essential for replication. When supplied in trans, repB of pWVO2 complemented a repB deficiency of pWVO5. Upstream of the repB gene, all these plasmids contain a strongly conserved region including a 22 bp sequence tandemly repeated three-and-a-half times, and an A/T-rich region. The similarity with pWVO2, which is known to replicate via a theta mechanism, suggests that all plasmids of this family are capable of theta replication. Southern hybridizations revealed that many lactococcal strains contain plasmids of this family.
ChopinA., ChopinM-C., Moillo-BattA., LangellaP.1984; Two plasmid-determined restrictionmodification systems in Streptococcus lactis. Plasmid 11:260–263
HayesF., VosP., FitzgeraldG. F., de VosW. M., DalyC.1991; Molecular organization of the minimal replicon of novel, narrow-host-range, lactococcal plasmid pCI305. Plasmid 25:16–26
HoloH., NesI. F.1989; High-frequency transformation, by electroporation, of Lactococcus lactis subsp. cremoris grown with glycine in osmotically stabilized media. Appl Environ Microbiol 55:3119–3123
JahnsA., SchaferA., GeisA., TeuberM.1991; Identification, cloningsequencing of the replication region of Lactococcus lactis ssp. lactis biovar. diacetylactis Bu2 citrate plasmid pSL2. FEMS Microbiol Lett 80:253–258
KiewietR., KokJ., SeegersJ. F. M. L., VenemaG., BronS.1993; The mode of replication is a major factor in segregational plasmid instability in Lactococcus lactis. Appl Environ Microbiol 59:358–364
KokJ.1991; Special -purpose vectors for lactococci. In GeneticsMolecular Biology of Streptococci, LactococciEnterococci pp. 97–102 Edited by DunnyG. M., ClearyP. P. , McKayL. L. Washington, DC: American Society for Microbiology;
LeenhoutsK. J., TolnerB., BronS., KokJ., VenemaG., SeegersJ. F. M. L.1991; Nucleotide sequencecharacterization of the broad-host-range lactococcal plasmid pWVOl. Plasmid 26:55–66
OttoR., de VosW. M., GavrieliJ.1983; Plasmid DNA in Streptococcus cremoris Wg2: influence of pH on selection in chemo- stats of a variant lacking a protease plasmid. Appl Environ Microbiol 43:1272–1277
PerriS., HelinskiD. R., ToukdarianA.1991; Interactions of plasmid-encoded replication initiation proteins with the origin of DNA replication in the broad host range plasmid RK2. J Biol Chem 266:12536–12543
ShortJ. M., FernandezJ. M., SorgeJ. A., HugeW. D.1988; ZAP: a bacteriophage expression vector with in vivo excision properties. Nucleic Acids Res 16:7583–7600
VisserS., ExterkateF. A., SlangenC. J., de VeerG. J. C. M.1986; Comparative study of action of cell wall proteinases from various strains of Streptococcus cremoris on bovine asl-, β-k- casein. Appl Environ Microbiol 52:1162–1166
Von WrightA., WesselsS., TynkknenS., SaarelaM.1990; Isolation of a replication region of a large lactococcal plasmiduse in cloning of a nisin resistance determinant. Appl Environ Microbiol 56:2029–2035