Comparative analysis of Enterococcus faecalis sex pheromone plasmids identifies a single homologous DNA region which codes for aggregation substance

An analysis of the 11 known sex pheromone plasmids of Enterococcusfaecalis was performed by DNA-DNA hybridization. Plasmids pAD1, pJH2, and pBEM10 turned out to be closely related, whereas pAM373 showed only weak homology with pADl. A comparison of the hemolysin/bacteriocin determinants of pAD1, pJH2, and pOB1 revealed strong similarities at the DNA level. Our main finding was that one DNA region is conserved among all sex pheromone plasmids, with pAM373 again being an exception; for pADi this region was shown earlier to code for aggregation substance. Detailed hybridization studies of the genes for this plasmid-coded adhesin, which is responsible for cell-cell contact during conjugative transfer via the so-called sex pheromone system of E. faecalis, support the idea of their common origin. A group of conjugative plasmids of Enterococcus faecalis which transfers at high frequencies (10-3 to 10-1) in broth matings has been described. Mating is triggered by sex pheromones (small, linear peptides) excreted into the me-dium by plasmid-free cells. These sex pheromones induce the synthesis of an adhesin called aggregation substance which appears on the surface of cells carrying the corre