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Formation of chromosomal tandem arrays of the SXT element and R391, two conjugative chromosomally integrating elements that share an attachment site.

ABSTRACT: The SXT element, a conjugative, self-transmissible, integrating element (a constin) originally derived from a Vibrio cholerae O139 isolate from India, and IncJ element R391, originally derived from a South African Providencia rettgeri isolate, were found to be genetically and functionally related. Both of these constins integrate site specifically into the Escherichia coli chromosome at an identical attachment site within the 5' end of prfC. They encode nearly identical integrases, which are required for chromosomal integration, excision, and extrachromosomal circularization of these elements, and they have similar tra genes. Therefore, these closely related constins have virtually identical mechanisms for chromosomal integration and dissemination. The presence of either element in a recipient cell did not significantly reduce its ability to acquire the other element, indicating that R391 and SXT do not encode surface exclusion determinants. In cells harboring both elements, SXT and R391 were integrated in tandem fashion on the chromosome, and homologous recombination appeared to play little or no role in the formation of these arrays. Interference between R391 and SXT was detected by measuring the frequency of loss of an unselected resident element upon introduction of a second selected element. In these assays, R391 was found to have a stronger effect on SXT stability than vice versa. The level of expression and/or activity of the donor and recipient integrases may play a role in the interference between these two related constins.

SUBMITTER: Hochhut B

PROVIDER: S-EPMC94984 | biostudies-literature | 2001 Feb

REPOSITORIES: biostudies-literature

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Formation of chromosomal tandem arrays of the SXT element and R391, two conjugative chromosomally integrating elements that share an attachment site.

Hochhut B B Beaber J W JW Woodgate R R Waldor M K MK

Journal of bacteriology 20010201 4

The SXT element, a conjugative, self-transmissible, integrating element (a constin) originally derived from a Vibrio cholerae O139 isolate from India, and IncJ element R391, originally derived from a South African Providencia rettgeri isolate, were found to be genetically and functionally related. Both of these constins integrate site specifically into the Escherichia coli chromosome at an identical attachment site within the 5' end of prfC. They encode nearly identical integrases, which are req ...[more]

PMID: 11157923

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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.

Dataset Information

Formation of chromosomal tandem arrays of the SXT element and R391, two conjugative chromosomally integrating elements that share an attachment site.

Publications

Formation of chromosomal tandem arrays of the SXT element and R391, two conjugative chromosomally integrating elements that share an attachment site.

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