LuxS/autoinducer-2 quorum sensing molecule regulates transcriptional virulence gene expression in Clostridium difficile

Toxigenic Clostridium difficile CCUG19126 produces the autoinducer-2 (AI-2) quorum sensing molecule that induces bioluminescence in Vibrio harveyi BB170 reporter strain. AI-2-containing cell-free supernatants from mid-log phase C. difficile and Escherichia coli DH5α expressing recombinant luxScd upregulated the transcript levels of tcdA (7-10-fold), tcdB (4-6-fold), and tcdE (2-3-fold) in early-log C. difficile. In contrast, no induction occurred when cells were exposed to sterile medium or to cell-free supernatant from E. coli DH5α. AI-2 did not significantly increase the level of toxin A in early-log C. difficile. These results suggest that LuxScd-dependent signaling regulates virulence gene expression at the transcriptional level in C. difficile.