ROLE OF B.FRAGILIS OXYGEN STRESS RESPONSE IN INFECTION

描述(申请人提供)：厌氧有机体，脆弱类杆菌，对氧气的毒性作用具有极强的抵抗力。这种抗性可归因于诱导氧化应激反应(OSR)，将对这种反应进行研究，以证明其在类杆菌感染的发病机制中的作用。预计新的自由基保护机制和新的抗氧化防御策略将被发现。这一观点得到了一个事实的支持，即脆弱芽孢杆菌很早就从其他真细菌中分离出来，并独立进化出了长期暴露在氧气中生存的能力。此外，由于这是一种厌氧菌，它可能对氧气保护有严格的要求，这导致了独特的高度保护抗氧化剂的开发。这项研究的长期目标是了解导致脆弱芽孢杆菌耐氧性的基本生理和遗传过程，以及这些过程是如何促进毒力的。这项建议的具体目标是：1)描述调控OxyR表达和功能的新机制。OxyR是一种氧化还原敏感的转录调节因子，调控OSR的表达。这一目标提出了对OxyR调节基因表达的独特机制进行分析。此外，我们将检验这一假设，即脆弱杆菌硫氧还蛋白系统是维持细胞氧化还原平衡的主要系统，因此它控制氧化应激响应调节蛋白的氧化还原状态，如OxyR。2)鉴定毛皮同系物在控制OSR中的作用。这一目标将检验这一假说，即脆弱芽孢杆菌中的三个毛皮同源物由于调节金属(Fe)稳态和其他OSR基因而在氧化应激过程中需要保护。3)阐明OSR在脆弱芽孢杆菌感染中的作用。这一目的将解决这样的假设，即OSR是启动感染和在宿主中持续所必需的。我们的方法由两个阶段组成，将在模拟两个不同感染阶段的动物模型中检查OSR突变对生存的影响。了解耐氧性可能有助于确定有效治疗脆弱芽孢杆菌感染的新抗生素靶标。例如，对硫氧还蛋白进行氧化还原控制的排他性依赖可能是针对硫氧还蛋白还原酶的药物所利用的弱点。

DESCRIPTION (provided by applicant): The anaerobic organism, Bacteroides fragilis is exceptionally resistant to the toxic effects of oxygen. This resistance can be attributed to induction of an oxidative stress response (OSR) and this response will be studied to document its role in the pathogenesis of Bacteroides infections. It is expected that new mechanisms of free radical protection and novel antioxidant defense strategies will be uncovered. This idea is supported by the fact that B. fragilis has diverged early from other eubacteria and has independently evolved the ability to survive extended exposure to oxygen. Further, since this is an anaerobe it is likely to have stringent requirements for oxygen protection that have resulted in the development of unique highly protective antioxidants. The long-term goals of this research are to understand the basic physiological and genetic processes responsible for B. fragilis oxygen tolerance and how these contribute to virulence. Specific objectives for this proposal are: 1) Delineate novel mechanisms that regulate expression and function of OxyR. OxyR is a redox sensitive transcriptional regulator that governs expression of the OSR. This aim proposes to pursue analysis of unique mechanisms through which OxyR regulates genes expression. In addition we will test the hypothesis that the B. fragilis thioredoxin system is the predominant system for maintaining the cellular redox balance and as such it controls the redox state of oxidative stress responsive regulatory proteins such as OxyR. 2) Characterize the role of Fur homologs in control of the OSR. This aim will test the hypothesis that the three Fur homologs in B. fragilis are required for protection during oxidative stress due to their regulation of metal (Fe) homeostasis and other OSR genes. 3) Elucidate a role for the OSR in B. fragilis infections. This aim will address the hypothesis that the OSR is necessary for initiation of infection and for persistence in the host. Our approach is composed of two phases that will examine the effect of OSR mutations on survival in animal models that mimic the two different stages of infection. Understanding oxygen tolerance may lead to identification of new antibiotic targets effective for treatment of B. fragilis infections. For example, exclusive dependence on thioredoxins for redox control may be a weakness that can be exploited by drugs targeted against thioredoxin reductase.