title: Salmonella genomic island 1 (SGI1) reshapes the mating apparatus of IncC conjugative plasmids to promote self-propagation.
abstract: IncC conjugative plasmids and Salmonella genomic island 1 (SGI1) and relatives are frequently associated with multidrug resistance of clinical isolates of pathogenic Enterobacteriaceae. SGI1 is specifically mobilized in trans by IncA and IncC plasmids (commonly referred to as A/C plasmids) following its excision from the chromosome, an event triggered by the transcriptional activator complex AcaCD encoded by these helper plasmids. Although SGI1 is not self-transmissible, it carries three genes, traNS, traHS and traGS, coding for distant homologs of the predicted mating pore subunits TraNC, TraHC and TraGC, respectively, encoded by A/C plasmids. Here we investigated the regulation of traNS and traHGS and the role of these three genes in the transmissibility of SGI1. Transcriptional fusion of the promoter sequences of traNS and traHGS to the reporter gene lacZ confirmed that expression of these genes is inducible by AcaCD. Mating experiments using combinations of deletion mutants of SGI1 and the helper IncC plasmid pVCR94 revealed complex interactions between these two mobile genetic elements. Whereas traNC and traHGC are essential for IncC plasmid transfer, SGI1 could rescue null mutants of each individual gene revealing that TraNS, TraHS and TraGS are functional proteins. Complementation assays of individual traC and traS mutants showed that not only do TraNS/HS/GS replace TraNC/HC/GC in the mating pore encoded by IncC plasmids but also that traGS and traHS are both required for SGI1 optimal transfer. In fact, remodeling of the IncC-encoded mating pore by SGI1 was found to be essential to enhance transfer rate of SGI1 over the helper plasmid. Furthermore, traGS was found to be crucial to allow DNA transfer between cells bearing IncC helper plasmids, thereby suggesting that by remodeling the mating pore SGI1 disables an IncC-encoded entry exclusion mechanism. Hence traS genes facilitate the invasion by SGI1 of cell populations bearing IncC plasmids.
authors.affiliation: Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Nicolas
authors.identifier: 0000-0001-6364-547X
authors.initials: N
authors.lastname: Carraro
authors.affiliation: Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Romain
authors.identifier: 0000-0002-7681-4727
authors.initials: R
authors.lastname: Durand
authors.affiliation: Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Nicolas
authors.identifier: 0000-0003-3764-5438
authors.initials: N
authors.lastname: Rivard
authors.affiliation: Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Charley
authors.identifier: 0000-0001-5241-5249
authors.initials: C
authors.lastname: Anquetil
authors.affiliation: Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Catherine
authors.initials: C
authors.lastname: Barrette
authors.affiliation: Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Malika
authors.identifier: 0000-0002-1841-7854
authors.initials: M
authors.lastname: Humbert
authors.affiliation: Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Vincent
authors.identifier: 0000-0001-6318-6904
authors.initials: V
authors.lastname: Burrus
mesh_terms: D002875:Chromosomes / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D044404:Genomic Islands / Q000235:genetics*; D020071:Interspersed Repetitive Sequences / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D019779:Salmonella enterica / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D017384:Sequence Deletion / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial