Quorum sensing is a phenomenon defined as gene regulation in response to cell density that regulates various functions in bacteria. The periodontopathogen Porphyromonas gingivalis possesses a luxS gene homologue that may encode a quorum-sensing system. In order to identify genes of P. gingivalis that are regulated by luxS, gene expression analysis was done using microarrays and RNA samples from the W83 wild-type strain and an isogenic luxS mutant, 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, including htrA, clpB, groEL, dnaK, and the F subunit of alkyl hydroperoxide reductase. This suggested that luxS is involved in stress gene regulation in P. 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 the P. gingivalis wild-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 that luxS might be involved in promoting survival of P. gingivalis in the host by regulating its response to host-induced stresses such as temperature, H2O2, and pH.
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机译：群体感应是一种定义为对细胞密度作出反应的基因调节现象，该细胞密度调节细菌的各种功能。牙周病原体牙龈卟啉单胞菌具有luxS基因同源物，可编码群体感应系统。为了鉴定受luxS调控的牙龈卟啉单胞菌的基因，使用来自W83野生型菌株和同基因的luxS突变体LY2001的微阵列和RNA样品进行基因表达分析。结果表明，LY2001中的17个开放阅读框（ORF）被上调而两个被下调。进行实时PCR以确认微阵列结果。在上调的ORF中有一组与压力相关的基因，包括htrA，clpB，groEL，dnaK和烷基氢过氧化物还原酶的F亚基。这表明luxS参与牙龈卟啉单胞菌的应激基因调控。对牙龈卟啉单胞菌野生型和LY2001菌株进行了应力响应实验，包括高温存活，对过氧化氢（H2O2）的抗性以及在暴露于低和高pH下的存活。在50°C的压力下，LY2001的存活率明显高于W83。在pH 5时没有发现差异，但是与在pH 9时的W83相比，LY2001的存活率增加了。当用0.35 mM H2O2胁迫时，LY2001的存活率也比W83好。这些结果表明，luxS可能通过调节其对宿主诱导的应激（例如温度，H2O2和pH）的响应来促进牙龈卟啉单胞菌在宿主中的存活。
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