pLS20 is the archetype of a new family of conjugative plasmids harboured byBacillusspecies

Abstract

Conjugation plays important roles in genome plasticity, adaptation and evolution but is also the major horizontal gene-transfer route responsible for spreading toxin, virulence and antibiotic resistance genes. A better understanding of the conjugation process is required for developing drugs and strategies to impede the conjugation-mediated spread of these genes. So far, only a limited number of conjugative elements have been studied. For most of them, it is not known whether they represent a group of conjugative elements, nor about their distribution patterns. Here we show that pLS20 from the Gram-positive bacterium Bacillus subtilis is the prototype conjugative plasmid of a family of at least 35 members that can be divided into four clades, and which are harboured by different Bacillus species found in different global locations and environmental niches. Analyses of their phylogenetic relationship and their conjugation operons have expanded our understanding of a family of conjugative plasmids of Gram-positive origin.

Establishment Genes Present on pLS20 Family of Conjugative Plasmids Are Regulated in Two Different Ways

“…One of these was based on the replication region and the other on a concatenated sequence of nine conserved orthologous genes. This analysis resulted in two very similar trees in which these plasmids were divided into four clades [11]. pLS20 belongs to clade I, together with 23 other plasmids, and p576 belongs to clade II, together with six other plasmids.…”

“…In those cases where the plasmid sequence was present in the database as one large linear contig that probably corresponds to most of the plasmid sequence, the name was extended with a single dagger. Names are extended with a double dagger symbol when the plasmid was reconstructed form two or several contigs [11]. Putative establishment regulons of the other clade II plasmids are approximately aligned with that of p576.…”

“…The work presented here also revealed two interesting differences between the genes of the pLS20 family plasmids that are involved in the first three steps of conjugation (i.e., recipient cell selection and attachment, synthesis of the translocation machinery, and DNA processing), and those corresponding to the fourth step of the conjugation process (i.e., establishment genes). First, there is an overall high level of similarity between the genes involved in the first three steps [11], but the establishment genes involved in step four tend to be more variable. Second, while the genes involved in the first three steps are all located in one single large operon, the establishment genes are distributed in multiple operons, which cluster together on the plasmid.…”

“…Although pLS20 is among the best-studied conjugative plasmids in G+ bacteria, its establishment genes have not been studied so far. Very recently, we have found that pLS20 is the prototype of a new family of conjugative plasmids that includes p576 [11]. The family has over 30 members and the plasmids are hosted by Bacillus species that are distributed worldwide.…”

Conjugation Operons in Gram-Positive Bacteria with and without Antitermination Systems

“…Recently, we reported that pLS20 is the prototype of a family of related plasmids and that the conjugation operons present on all these plasmids (i) contain multiple intrinsic terminators and (ii) start with a processive antitermination (P-AT) system, named conAn [ 30 , 31 ]. The conAn system contributes to the strictly controlled expression of the conjugation genes by minimizing the effects of spurious transcription and allowing the differential expression of subsets of genes within the conjugation operon.…”