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Evolution of a self-inducible cytolethal distending toxin type V-encoding bacteriophage from Escherichia coli O157:H7

Anna Allué-Guardia1, Lejla Imamovic, Maite Muniesa

  • 1Department of Microbiology, University of Barcelona, Barcelona, Spain.

Journal of Virology
|October 11, 2013
PubMed

Insights

Researchers discovered a new bacteriophage, ΦAA91, carrying Shiga toxin genes. This phage evolved in Shigella sonnei, gaining enhanced lysogenic abilities and potentially contributing to new pathogenic strains.

Area of Science:

  • Microbiology
  • Virology
  • Genetics

Background:

  • Bacteriophages carrying virulence genes, likecdt genes, play a role in bacterial pathogenicity.
  • Limited understanding exists regarding the transfer mechanisms of these genes due to a scarcity of described inducible Cdt phages.

Purpose of the Study:

  • To investigate the mechanisms of cdt gene transfer mediated by bacteriophages.
  • To characterize a novel self-inducible Cdt phage and its evolution after host transfer.

Main Methods:

  • Isolation and characterization of a novel Myoviridae Cdt phage (ΦAA91) from Escherichia coli.
  • Lysogenization of a cdt-negative Shigella sonnei strain with ΦAA91 to generate ΦAA91-ss.
  • Genome sequencing of ΦAA91-ss and analysis of genetic elements, including an IS21 insertion.
  • Infection and lysogenization assays of ΦAA91-ss across a collection of bacterial strains.

Main Results:

  • A new self-inducible Cdt phage, ΦAA91, was isolated and its derivative, ΦAA91-ss, was generated in Shigella sonnei.
  • ΦAA91-ss demonstrated broad infectivity (59.6%) and lysogenization capability (22.8%) in diverse bacterial strains.
  • Genome sequencing revealed ΦAA91-ss has a P2-like structure with the cdt operon near cosR and an IS21 insertion truncating the cox gene.
  • The IS21 element, absent in the original phage, was acquired after transduction in Shigella, enhancing lysogenic potential.

Conclusions:

  • Temperate bacteriophages carrying virulence genes can evolve upon infecting new hosts, acquiring enhanced lysogenic abilities.
  • The observed evolution of ΦAA91-ss in Shigella sonnei provides empirical evidence for the emergence of new pathogenic strains through phage-mediated gene transfer.

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