Conjugation in Gram-positive bacteria

Most bacteria contain one or more autonomously replicating units called plasmids, which have a modular structure. Besides an essential DNA replication module, many plasmids contain a conjugation module containing all the genes required for transfer of the plasmid from a donor to a recipient cell via a connecting pore. These plasmids, named conjugative plasmids, often contain toxin, virulence and/or antibiotic resistance genes. Conjugation is the main horizontal gene transfer route responsible for the spread of these genes. Particularly antibiotic resistance is an increasing global problem affecting the health of humans and animals and causing large economic losses. Understanding different aspects of the conjugation process is essential for designing strategies or drugs to combat conjugation-mediated spread of antibiotic resistance. Little is known about conjugation in Gram-positive (G+) bacteria, which is why started to study this topic several years ago. Our studies were initially focused on plasmid pLS20 from Bacillus subtilis, but recently we found that pLS20 is the prototype of a family of related plasmids that allowed broadening our studies. Conjugation can be divided into four steps: (i) recognition/attachment of the donor to the recipient cell, (ii) producing the channel through which the DNA is transferred, (iii) generating the ssDNA that is transferred, and (iv) establishment in the new host. We address all these steps in our studies using a multidisciplinary approach in collaboration with other laboratories. One of our recent discoveries is that most conjugation operons possess a novel two-component antitermination system essential for proper expression of the conjugation genes. This discovery changes our view on conjugation-related spread of antibiotic resistance.