Promoter analysis of cytolethal distending toxin genes (cdtA, B, and C) and effect of a luxS mutation on CDT production in Campylobacter jejuni

Quorum sensing is known to be related to regulation of virulence factors in some pathogens. We report transcriptional analysis of cdt genes (cdtA, B, and C) encoding cytolethal distending toxin (CDT) in Campylobacter jejuni and demonstrate that a luxS mutation affects the cdt transcription in C. jejuni. The reverse transcriptase-polymerase chain reaction (RT-PCR) showed that cdtA, cdtB, and cdtC genes constitute a polycistronic operon in C. jejuni. A putative transcriptional start site was found at 81-bp upstream from the start codon of cdtA by the primer extension assay. A decrease in cdt transcription was observed in the luxS null mutant, which is defective in AI-2 production. The level of cdt transcription in the luxS mutant was approximately 61% of that in the wild-type. Flow cytometric analysis showed that the number of HeLa cells arrested in the G₂/M phase, a common biological feature of CDT activity, was reduced by treatment with the cell-free supernatant of the luxS mutant as compared to that of the wild-type. Our observations suggest that the function of luxS is related to the regulation of cdt in C. jejuni.