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The complexity and diversity of the Pathogenicity Locus in Clostridium difficile clade 5
Briony Elliott1, Kate E Dingle2, Xavier Didelot3
1Microbiology and Immunology, School of Pathology and Laboratory Medicine, The University of Western Australia, Crawley, Western Australia, Australia briony.elliott@uwa.edu.au.
Genome Biology and Evolution
|November 10, 2014
Summary
The Pathogenicity Locus (PaLoc) in Clostridium difficile clade 5 has a complex evolutionary history, involving at least two distinct acquisition events and evidence of recombination. This sheds light on the emergence of pathogenic strains.
Area of Science:
- Microbiology
- Evolutionary Biology
- Genomics
Background:
- Clostridium difficile infection symptoms are driven by toxins TcdA and TcdB, encoded by the Pathogenicity Locus (PaLoc).
- The PaLoc is a mobile genetic element with variable presence across C. difficile strains.
- Clade 5 strains include emergent, highly pathogenic C. difficile genotypes linked to human and animal infections.
Purpose of the Study:
- To investigate the evolutionary history of the PaLoc specifically within Clostridium difficile clade 5.
- To understand the origins and diversification of PaLoc variants in pathogenic C. difficile.
Main Methods:
- Phylogenetic analyses of PaLoc variants and adjacent genomic regions in clade 5 strains.
- Comparison of core genome and PaLoc phylogenies between clade 5 and other C. difficile clades.
- Annotation of PaLoc variants using a collection of toxigenic and nontoxigenic strains.
Main Results:
- Identified two distinct PaLoc acquisition events in clade 5: one for toxin A(+)B(+) and another for A(-)B(+).
- Evidence of homologous recombination within the PaLoc and surrounding regions, both between clade 5 lineages and with other clades.
- Suggests PaLoc loss via recombination and acquisition of a variant holin gene in the A(-)B(+) PaLoc through allelic exchange.
Conclusions:
- The PaLoc in C. difficile clade 5 exhibits a complex evolutionary trajectory marked by multiple acquisition and recombination events.
- Genetic diversity within clade 5 PaLoc is extensive, indicating ancient origins and a dynamic evolutionary past.
- Understanding PaLoc evolution is crucial for tracking the emergence and spread of highly pathogenic C. difficile strains.
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