Analysis of Al-2/LuxS-dependent transcription in Campylobacter jejuni strain 81-176

Autoinducer-2 (Al-2) is a quorum-sensing signal molecule that controls a variety of cellular activities in response to cell density in both gram-negative and gram-positive bacteria. The production of Al-2 is dependent upon LuxS, the last enzyme in the Al-2 biosynthesis pathyway. For this study, we constructed a luxS null mutation (Delta luxS) in Campylobacter jejuni strain 81-176, and showe that it abolished Al-2 production. The Delta luxS mutant had a longer doubling time in Mueller-Hinton (MH) broth and reduced swarming on MH soft agar at 37 degrees C compared to the wild type (wt), whereas growth rate or swarming at 42 degrees C was not affected. The Delta luxS mutant was also more sensitive to hydrogen peroxide (H2O2) and cumene hydroperoxide than the wt by disc inhibition assays at 42 degrees C, though minimum inhibitory concentration comparisons were inconclusive. Differences in genome-wide gene expression between wt and Delta luxS mutant with and without H2O2 treatments were compared using DNA microarrays. The genes that showed differential expressions (wt/Delta luxS) include operons/pathways involved in AI-2 synthesis and S-adenosylmethionine (SAM) metabolism (metE, metF, and pfs), flagellar assembly/regulation, stress response (ahpC, tpx, and groES), ABC transporters/efflux systems, and two genes of unknown function located downstream of luxS (Cj1199 and Cj1200). The wt/Delta luxS expression ratios of ahpC (encoding alkyl hydroperoxide reductase) and tpx (encoding thiol peroxidase) were increased only with H2O2 treatment, consistent with our finding that the Delta luxS mutant exhibits higher sensitivity to oxidative stress than wt. Our microarray results agreed with the Delta luxS mutant phenotypes, and suggested that LuxS plays a role in central metabolism involving SAM metabolism, but it is uncertain whether Al-2 functions as a true quorum-sensing signal in C. jejuni.