Virulence Gene Regulation by the agr System in Clostridium perfringens

A gram-positive anaerobic pathogen, Clostridium perfringens, causes clostridial myonecrosis or gas gangrene in humans by producing numerous extracellular toxins and enzymes that act in concert to degrade host tissue. The agr system is known to be important for the regulation of virulence genes in a quorum-sensing manner in Staphylococcus aureus. A homologue for S. aureus agrBD (agrBD(Sa)) was identified in the C. perfringens strain 13 genome, and the role of C. perfringens agrBD (agrBD(Cp)) was examined. The agrBD(Cp) knockout mutant did not express the theta-toxin gene, and transcription of the alpha- and kappa-toxin genes was also significantly decreased in the mutant strain. The mutant strain showed a recovery of toxin production after the addition of the culture supernatant of the wild-type strain, indicating that the agrBD(Cp) mutant lacks a signal molecule in the culture supernatant. An agr-virR double-knockout mutant was constructed to examine the role of the VirR/VirS two-component regulatory system, a key virulence regulator, in agrBD(Cp)-mediated regulation of toxin production. The double-mutant strain could not be stimulated for toxin production with the wild-type culture supernatant. These results indicate that the agrBD(Cp) system plays an important role in virulence regulation and also suggest that VirR/VirS is required for sensing of the extracellular signal and activation of toxin gene transcription in C. perfringens.