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Summary

Clostridioides difficile toxin genes show modular evolution, with TcdB variants correlating to cell damage. The binary toxin gene region also exhibits variability and potential exchange between strains.

Keywords:
CdtLocClostridioides difficilePaLocevolutiontoxin genetoxinotypes

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Area of Science:

  • Microbiology
  • Evolutionary Biology
  • Genetics

Background:

  • Clostridioides difficile causes hospital-acquired diarrhea, with toxins TcdA and TcdB being key virulence factors encoded by the PaLoc region.
  • The binary toxin (from CdtLoc) also contributes to C. difficile pathogenicity.
  • Toxinotype variations reflect genetic diversity within C. difficile toxin-encoding regions.

Purpose of the Study:

  • To analyze evolutionary relationships of C. difficile toxin gene variants.
  • To investigate mechanisms of variability in toxin genes and the PaLoc region.
  • To explore the structure-function relationship of TcdB variants.

Main Methods:

  • Comprehensive analysis of known C. difficile toxinotypes.
  • Phylogenetic analysis of toxin gene domains and core genome.
  • Mapping mutations onto the 3D structure of TcdB.

Main Results:

  • Toxin genes exhibit modular structures with domains having different evolutionary histories.
  • Four mutation patterns in TcdB correlated with distinct cytopathic effects (CPE) on cells.
  • Variations in TcdB primarily occur at surface residues, with residue 449 impacting CPE type.
  • CdtLoc phylogenies align with core genome, suggesting potential horizontal gene transfer.

Conclusions:

  • C. difficile toxin genes evolve through modular recombination, influencing virulence.
  • TcdB structure-function relationships are linked to specific mutations and cellular effects.
  • The CdtLoc region shows evolutionary patterns consistent with core genome, but also evidence of exchange.