Conjugation in Gram-Positive Bacteria

Abstract

This chapter discusses conjugative systems in various gram-positive genera, and includes some discussion of conjugative transposons insofar as they assume a plasmid-like (circular) intermediate structure during movement. The pheromone-responding plasmids, which frequently encode antibiotic resistance traits as well as the production of cytolysins or bacteriocins, are commonly found in Enterococcus faecalis. The plasmids that have been studied in the greatest detail with respect to regulation of the pheromone response are pADl, pCFlO, pPDl, and pAM373. The hemolysin/bactcriocin (cytolysin)-encoding plasmids exemplified by the well-characterized pADl represent a large and globally disseminated family of pheromone-responding plasmids. Analysis of the sequence suggests an important role for insertion sequence elements in its evolution insofar as the conjugation genes, bacteriocin production genes, and bacteriophage resistance and plasmid maintenance functions are organized in three different regions separated by insertion sequence elements. The mob-oriT region is essential for the pBC16 mobilization by several other Bacillus conjugative plasmids, such as pLS20, pHT73, or pAW63, and represents functions generally required for the transfer of mobilizable plasmids by self-transmissible plasmids in gram-negative and other gram-positive bacteria. The growing problem of multiple antibiotic resistance among human and animal pathogens is a classic example of how quickly horizontal gene transfer can relate to serious health issues.