Dataset Information

Identification of the origin of transfer (oriT) and a new gene required for mobilization of the SXT/R391 family of integrating conjugative elements.

ABSTRACT: Integrating conjugative elements (ICEs) are self-transmissible, mobile elements that are widespread among bacteria. Following their excision from the chromosome, ICEs transfer by conjugation, a process initiated by a single-stranded DNA break at a specific locus called the origin of transfer (oriT). The SXT/R391 family of ICEs includes SXT(MO10), R391, and more than 25 related ICEs found in gammaproteobacteria. A previous study mapped the oriT locus of SXT(MO10) to a 550-bp intergenic region between traD and s043. We suspected that this was not the correct oriT locus, because the identical traD-s043 region in R391 and other SXT/R391 family ICEs was annotated as a gene of an unknown function. Here, we investigated the location and structure of the oriT locus in the ICEs of the SXT/R391 family and demonstrated that oriT(SXT) corresponds to a 299-bp sequence that contains multiple imperfect direct and inverted repeats and is located in the intergenic region between s003 and rumB'. The oriT(SXT) locus is well conserved among SXT/R391 ICEs, like R391, R997, and pMERPH, and cross-recognition of oriT(SXT) and oriT(R391) by R391 and SXT(MO10) was demonstrated. Furthermore, we identified a previously unannotated gene, mobI, located immediately downstream from oriT(SXT), which proved to be essential for SXT(MO10) transfer and SXT(MO10)-mediated chromosomal DNA mobilization. Deletion of mobI did not impair the SXT(MO10)-dependent transfer of the mobilizable plasmid CloDF13, suggesting that mobI has no role in the assembly of the SXT(MO10) mating pair apparatus. Instead, mobI appears to be involved in the recognition of oriT(SXT).

SUBMITTER: Ceccarelli D

PROVIDER: S-EPMC2493277 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Identification of the origin of transfer (oriT) and a new gene required for mobilization of the SXT/R391 family of integrating conjugative elements.

Ceccarelli Daniela D Daccord Aurélie A René Mélissa M Burrus Vincent V

Journal of bacteriology 20080606 15

Integrating conjugative elements (ICEs) are self-transmissible, mobile elements that are widespread among bacteria. Following their excision from the chromosome, ICEs transfer by conjugation, a process initiated by a single-stranded DNA break at a specific locus called the origin of transfer (oriT). The SXT/R391 family of ICEs includes SXT(MO10), R391, and more than 25 related ICEs found in gammaproteobacteria. A previous study mapped the oriT locus of SXT(MO10) to a 550-bp intergenic region bet ...[more]

PMID: 18539733

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Project description:Integrative and conjugative elements (ICEs) of the SXT/R391 family are key drivers of the spread of antibiotic resistance in Vibrio cholerae, the infectious agent of cholera, and other pathogenic bacteria. The SXT/R391 family of ICEs was defined based on the conservation of a core set of 52 genes and site-specific integration into the 5' end of the chromosomal gene prfC Hence, the integrase gene int has been intensively used as a marker to detect SXT/R391 ICEs in clinical isolates. ICEs sharing most core genes but differing by their integration site and integrase gene have been recently reported and excluded from the SXT/R391 family. Here we explored the prevalence and diversity of atypical ICEs in GenBank databases and their relationship with typical SXT/R391 ICEs. We found atypical ICEs in V. cholerae isolates that predate the emergence and expansion of typical SXT/R391 ICEs in the mid-1980s in seventh-pandemic toxigenic V. cholerae strains O1 and O139. Our analyses revealed that while atypical ICEs are not associated with antibiotic resistance genes, they often carry cation efflux pumps, suggesting heavy metal resistance. Atypical ICEs constitute a polyphyletic group likely because of occasional recombination events with typical ICEs. Furthermore, we show that the alternative integration and excision genes of atypical ICEs remain under the control of SetCD, the main activator of the conjugative functions of SXT/R391 ICEs. Together, these observations indicate that substitution of the integration/excision module and change of specificity of integration do not preclude atypical ICEs from inclusion into the SXT/R391 family.IMPORTANCEVibrio cholerae is the causative agent of cholera, an acute intestinal infection that remains to this day a world public health threat. Integrative and conjugative elements (ICEs) of the SXT/R391 family have played a major role in spreading antimicrobial resistance in seventh-pandemic V. cholerae but also in several species of Enterobacteriaceae Most epidemiological surveys use the integrase gene as a marker to screen for SXT/R391 ICEs in clinical or environmental strains. With the recent reports of closely related elements that carry an alternative integrase gene, it became urgent to investigate whether ICEs that have been left out of the family are a liability for the accuracy of such screenings. In this study, based on comparative genomics, we broaden the SXT/R391 family of ICEs to include atypical ICEs that are often associated with heavy metal resistance.

Project description:Integrative and conjugative elements (ICEs) of the SXT/R391 family are the main contributors to acquired multidrug resistance in the seventh pandemic lineage of Vibrio cholerae, the etiological agent of the diarrheal disease cholera. Conjugative transfer of SXT/R391 ICEs is triggered by antibiotics and agents promoting DNA damage through RecA-dependent autoproteolysis of SetR, an ICE-encoded ? CI-like repressor. Here, we describe the role of CroS, a distant ? Cro homolog, as a key component contributing to the regulation of expression of the activator SetCD that orchestrates the expression of the conjugative transfer genes. We show that deletion of croS abolishes the SOS response-dependent induction of SXT despite the presence of a functional setR gene. Using quantitative reverse transcription-PCR and lacZ reporter assays, we also show that CroS represses setR and setCD expression by binding to operator sites shared with SetR. Furthermore, we provide evidence of an additional operator site bound by SetR and CroS. Finally, we show that SetCD expression generates a positive feedback loop due to SXT excision and replication in a fraction of the cell population. Together, these results refine our understanding of the genetic regulation governing the propagation of major vectors of multidrug resistance.Healthcare systems worldwide are challenged by an alarming drug resistance crisis caused by the massive and rapid propagation of antibiotic resistance genes and the associated emergence of multidrug-resistant pathogenic bacteria. SXT/R391 ICEs contribute to this phenomenon not only in clinical and environmental vibrios but also in several members of the family Enterobacteriaceae. We have identified and characterized here the regulator CroS as a key factor in the stimulation of conjugative transfer of these ICEs in response to DNA-damaging agents. We have also untangled conflicting evidence regarding autoactivation of transfer by the master activator of SXT/R391 ICEs, SetCD. Discovery of CroS provides a clearer and more complete understanding of the regulatory network that governs the dissemination of SXT/R391 ICEs in bacterial populations.

Dataset Information

Identification of the origin of transfer (oriT) and a new gene required for mobilization of the SXT/R391 family of integrating conjugative elements.

Publications

Identification of the origin of transfer (oriT) and a new gene required for mobilization of the SXT/R391 family of integrating conjugative elements.

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