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Characterization of the stable maintenance of the Shigella flexneri plasmid pHS-2
1Département de Microbiologie et Immunologie, Faculté de médecine, Université de Montréal, C.P. 6128, succ. Centre-Ville, Montréal, Québec, H3C 3J7, Canada.
Abstract:
pHS-2 is a 3-kb plasmid originally isolated from Shigella flexneri infections associated with reactive arthritis in humans. This plasmid is stably maintained in many clinical isolates of Shigella flexneri. The nucleotide sequence of this plasmid displays two closely linked regions that may play a role in the maintenance of this plasmid. One region consists of a 250-bp locus showing a significant homology to the ColE1 cer site. The results indicate that the cer-like site of pHS-2, like the ColE1 cer site, acts as a recA-independent, site-specific recombination site involved in the resolution of multimers, requiring the presence of the host-encoded factors ArgR, PepA, XerC, and XerD. The second region consists of a 36-kDa open reading frame involved in generating resistance to the bactericidal effect of complement, which confers a selective advantage to cells containing this sequence. The results also indicate that pHS-2 can replicate in another species of Enterobacteriaceae (Escherichia coli) and is mobilized by the F plasmid.
Insights
The pHS-2 plasmid from Shigella flexneri aids in resolving DNA multimers and provides complement resistance. This plasmid is stably maintained and can replicate in E. coli.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- pHS-2 is a plasmid isolated from Shigella flexneri, a pathogen linked to reactive arthritis.
- This plasmid is frequently found in clinical Shigella flexneri isolates, indicating stable maintenance.
- Understanding plasmid maintenance and function is crucial for studying bacterial pathogenesis.
Purpose of the Study:
- To investigate the functional regions of the pHS-2 plasmid involved in its maintenance and host interactions.
- To characterize the role of a cer-like site in plasmid stability and multimer resolution.
- To identify genetic elements contributing to bacterial survival in host environments.
Main Methods:
- Plasmid DNA sequencing and analysis.
- Site-specific recombination assays using host factors (ArgR, PepA, XerC, XerD).
- Functional studies on open reading frames related to bacterial defense mechanisms.
Main Results:
- pHS-2 contains a 250-bp cer-like site mediating recA-independent, site-specific recombination for multimer resolution.
- This recombination requires host factors ArgR, PepA, XerC, and XerD.
- A 36-kDa open reading frame confers resistance to complement, providing a selective advantage.
- pHS-2 replicates in Escherichia coli and is mobilized by the F plasmid.
Conclusions:
- The pHS-2 plasmid possesses a functional cer-like site crucial for its stable inheritance.
- Complement resistance encoded by pHS-2 enhances bacterial survival, potentially aiding infection.
- pHS-2 exhibits broad host range within Enterobacteriaceae and is transferable via conjugation.