Quorum Sensing in Group B Streptococcus

描述（由申请人提供）：B群链球菌（无乳链球菌或GBS）是革兰氏阳性新生儿脑膜炎的主要原因，也是老年人和慢性病成年人严重感染的一个日益重要的原因。虽然GBS通常表现为一种无害的共生菌，在近三分之一的成年女性的胃肠道和生殖道中定居，但它有能力在易感宿主中产生危及生命的感染。与GBS从无害的共生病原体转变为侵袭性病原体相关的因素尚不清楚，但可能涉及对不同宿主环境中遇到的特定线索作出反应的一系列细菌机制。据推测，革兰氏阳性和革兰氏阴性细菌通过分泌LuxS依赖的AI-2信号分子来利用密度依赖的传感机制（称为“群体感应”），该信号分子与其他生物体进行通信并调节细菌基因表达。我们已经鉴定并构建了GBS中LuxS同源物的非极性缺失突变体。与野生型亲本菌株相比，luxS缺失突变体在哈维弧菌的AI-2报告菌株中产生的生物发光减少，这表明GBS能够响应依赖luxS的AI-2信号分子。本提案的总体目标是：(1)确定由LuxS依赖的AI-2信号分子调控的GBS基因阵列，并确定AI-2分子对GBS毒力的贡献；(2)确定LuxS依赖的AI-2信号分子调控GBS基因表达的分子机制。这些目标将通过以下方式实现：(A)通过微阵列分析比较野生型GBS和等基因luxS缺失突变体的转录体，随后进行小鼠致病性研究，评估AI-2对毒力的贡献；(B)构建受luxS依赖的AI-2信号分子调控的基因融合体，以确定luxS依赖的AI-2分子是否通过细胞外积累实现基因调控。

DESCRIPTION (provided by applicant): Group B Streptococcus (Streptococcus agalactiae or GBS) is the leading cause of gram positive neonatal meningitis and is an increasingly important cause of serious infection in elderly and chronically ill adults. Although GBS usually behaves as a harmless commensal colonizing the gastrointestinal and genital tracts of nearly a third of adult women, it has the capacity to produce life-threatening infection in susceptible hosts. The factors associated with the transition of GBS from harmless commensal to invasive pathogen are not known but are likely to involve a repertoire of bacterial mechanisms that respond to specific cues encountered in various host environments. It has been speculated that gram-positive and gram-negative bacteria utilize a density-dependent sensing mechanism (termed "quorum sensing") through secretion of a LuxS dependent AI-2 signaling molecule that communicates with other organisms as well as regulates bacterial gene expression. We have identified and constructed a non-polar deletion mutant in a LuxS homolog in GBS. The luxS deletion mutant produces decreased bioluminescence in an AI-2 reporter strain of Vibrio harveyi compared to the wild type parent strain suggesting that GBS is capable of responding to the LuxS dependent AI-2 signaling molecule. The overall objectives of this proposal are to (1) determine the array of GBS genes regulated by the LuxS dependent AI-2 signaling molecule as well as determine the contribution of the AI-2 molecule to GBS virulence and (2) determine the molecular mechanism by which the LuxS dependent AI-2 signaling molecule regulates GBS gene expression. These objectives will be achieved by (A) comparing the transcriptisomes of wild type GBS and an isogenic luxS deletion mutant by microarray analysis followed by mouse lethality studies to assess the contribution of AI-2 to virulence and (B) constructing reporter fusions in genes regulated in response to the LuxS dependent AI-2 signaling molecule to determine if gene regulation is achieved by extracellular accumulation of a LuxS dependent AI-2 molecule.