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Laboratory Techniques Used to Maintain and Differentiate Biotypes of Vibrio cholerae Clinical and Environmental Isolates
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Laboratory Techniques Used to Maintain and Differentiate Biotypes of Vibrio cholerae Clinical and Environmental Isolates

Published on: May 30, 2017

Three pathogenicity islands of Vibrio cholerae can excise from the chromosome and form circular intermediates

Ronan A Murphy1, E Fidelma Boyd

  • 1Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA.

Journal of Bacteriology
|November 13, 2007
PubMed

Insights

Vibrio pathogenicity islands (VPI-2, VSP-I, VSP-II) can excise from the V. cholerae chromosome. This excision, requiring specific integrases, is a key step for horizontal gene transfer and potential pandemic spread.

Area of Science:

  • Microbiology
  • Genetics
  • Molecular Biology

Background:

  • Vibrio pathogenicity island-2 (VPI-2) is a 57-kb genomic region found in pandemic Vibrio cholerae isolates.
  • VPI-2 is integrated at a transfer RNA (tRNA)-serine locus and encodes genes for sialic acid metabolism, including neuraminidase, which unmasks the cholera toxin receptor.
  • Other Vibrio seventh pandemic islands (VSP-I and VSP-II) are also present in pandemic strains and integrate at tRNA loci.

Purpose of the Study:

  • To investigate the excision mechanism of VPI-2, VSP-I, and VSP-II from the Vibrio cholerae genome.
  • To determine the role of specific integrases in the excision process.
  • To understand the potential for horizontal gene transfer of these pathogenicity islands.

Main Methods:

  • Analysis of sequenced V. cholerae genomes to identify variants of VPI-2, VSP-I, and VSP-II.
  • Inverse nested PCR to detect extrachromosomal circular intermediate (CI) molecules.
  • Construction of knockout mutants for integrase genes (e.g., VC1758 for VPI-2) to assess their necessity for excision.

Main Results:

  • VPI-2, VSP-I, and VSP-II were all shown to excise from the V. cholerae chromosome, forming circular intermediate molecules.
  • Excision of VPI-2 and VSP-II requires their respective cognate P4-like integrases.
  • VSP-I, although not integrated at a tRNA locus and encoding a XerDC-like recombinase, also undergoes excision.

Conclusions:

  • All three major Vibrio pathogenicity islands (VPI-2, VSP-I, VSP-II) possess the capability to excise from the host chromosome.
  • Integrase-mediated excision is a crucial step preceding the horizontal transfer of these pathogenicity islands.
  • Understanding these excision mechanisms provides insights into the evolution and spread of Vibrio cholerae.

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