Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2008
Publication Date: August 1, 2008
Citation: He, Y., Frye, J.G., Strobaugh Jr, T.P., Chen, C. 2008. Ai-2/luxs dependent transcriptional profiling in campylobacter jejuni 81-176. Foodborne Pathogens and Disease. 5(4):399-415. Interpretive Summary: Campylobacter jejuni is a major cause of food-borne illness in the US. Although this bacterium is difficult to cultivate in the laboratory, it can survive in food and in the environment for a long period of time. Thus, it is important to study how Campylobacter interacts with its environment and with other bacteria to develop strategies for its control. Bacteria produce and sense small signaling molecules called autoinducers that have an effect on their growth, survival, and disease-causing potential through a process known as quorum-sensing. We utilized DNA microarrays, a genetic analysis tool, to study the regulation of genes that may be controlled by autoinducer AI-2 to gain insights on the role of quorum sensing in Campylobacter. Changes observed in a Campylobacter mutant lacking production of AI-2 were related to growth, motility, sensitivity to hydrogen peroxide. This information may be useful to develop strategies to modulate quorum sensing to prevent the growth and survival of Campylobacter in food and in the environment.
Technical Abstract: Autoinducer-2 (AI-2) is an universal quorum-sensing signal molecule which controls a variety of cellular activities in response to cell density in both Gram-negative and Gram-positive bacteria. The production of AI-2 is dependent upon LuxS, the key enzyme in the AI-2 biosynthesis pathway and the activated methyl cycle. In this study, we constructed a luxS deletion mutant in the food-borne pathogen, Campylobacter jejuni strain 81-176, and confirmed that there was no AI-2 production in this mutant. The luxS deletion mutant had longer doubling times at 37 and 42-degree C, 12 and 14 min. longer, respectively, and reduced motility as measured by smaller swimming/swarming halos at 37-degree C compared to the wild-type. The luxS deletion mutant was also more sensitive to hydrogen peroxide and cumene hydroperoxide (CHP) (MIC 2- to 4-fold lower) than the wild-type. To gain a better understanding of the mechanism of AI-2/LuxS-dependent quorum sensing and to reveal the role of AI-2/LuxS in the oxidative stress response in C. jejuni, differences in genome-wide gene expression between the wild-type and luxS deletion mutant were compared using DNA microarrays with and without exposure to hydrogen peroxide. The genes that exhibited AI-2/LuxS-dependent expression patterns included operons/pathways involved in AI-2 synthesis and the active methyl cycle (metE, metF, metK, pfs), flagellar proteins or flagella-related proteins, ABC transporters (pstB, pstS, pstA), and membrane proteins of an efflux system, as well as genes of unknown function located downstream of luxS (Cj1199 and Cj1200). The expression of ahpC (encoding alkyl hydroperoxide reductase) and tpx (encoding thio peroxidase) were increased only in the presence of the luxS gene and with hydrogen peroxide treatment, which is consistent with our finding that the luxS deletion mutant exhibits higher sensitivity to oxidative stress than the wild-type. Our results confirm that LuxS plays an important role in central metabolism involving methyl cycles, and that AI-2 may not function as a true quorum sensing signal in C. jejuni.