PLASMID INTEGRATION IN A WIDE-RANGE OF BACTERIA MEDIATED BY THE INTEGRASE OF LACTOBACILLUS-DELBRUECKII BACTERIOPHAGE-MV4

Bacteriophage mv4 is a temperate phage infecting Lactobacillus delbrue ckii subsp. bulgaricus. During lysogenization, the phage integrates it s genome into the host chromosome at the 3' end of a tRNA(Ser) gene th rough a site-specific recombination process (L. Dupont et al., J. Bact eriol. 177:586-595, 1995). A nonreplicative vector (pMC1) based on the mv4 integrative elements (attP site and integrase-coding int gene) is able to integrate into the chromosome of a wide range of bacterial ho sts, including Lactobacillus plantarum, Lactobacillus casei (two strai ns), Lactococcus lactis subsp, cremoris, Enterococcus faecalis, and St reptococcus pneumoniae. Integrative recombination of pMC1 into the chr omosomes of all of these species is dependent on the int gene product and occurs specifically at the pMC1 attP site, The isolation and seque ncing of pMC1 integration sites from these bacteria showed that in lac tobacilli, pMC1 integrated into the conserved tRNA(Ser) gene. In the o ther bacterial species where this tRNA gene is less or not conserved, secondary integration sites either in potential protein-coding regions or in intergenic DNA were used. A consensus sequence was deduced from the analysis of the different integration sites. The comparison of th ese sequences demonstrated the flexibility of the integrase for the ba cterial integration site and suggested the importance of the trinucleo tide CCT at the 5' end of the core in the strand exchange reaction.