Microarray Analysis of Quorum-Sensing-Regulated Genes inPorphyromonas gingivalis

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Abstract
Quorum sensing is a phenomenon defined as gene regulation in response to cell density that regulates various functions in bacteria. The periodontopathogenPorphyromonas gingivalispossesses aluxSgene homologue that may encode a quorum-sensing system. In order to identify genes ofP. gingivalisthat are regulated byluxS, gene expression analysis was done using microarrays and RNA samples from the W83 wild-type strain and an isogenicluxSmutant, LY2001. The results indicated that 17 open reading frames (ORFs) in LY2001 are upregulated and two are downregulated. Real-time PCR was done to confirm the microarray results. Among the upregulated ORFs is a group of stress-related genes, includinghtrA,clpB,groEL,dnaK, and the F subunit of alkyl hydroperoxide reductase. This suggested thatluxSis involved in stress gene regulation inP. gingivalis. Stress response experiments, including high-temperature survival, resistance to hydrogen peroxide (H2O2), and survival during exposure to low and high pH, were performed on theP. gingivaliswild-type and LY2001 strains. LY2001 had a significantly higher survival rate than did W83 when stressed at 50°C. No difference was found at pH 5, but LY2001 had increased survival compared to W83 at pH 9. LY2001 also survived better than W83 when stressed with 0.35 mM H2O2. These results suggest thatluxSmight be involved in promoting survival ofP. gingivalisin the host by regulating its response to host-induced stresses such as temperature, H2O2, and pH.