Probing the role of commensal intestinal fungi during Salmonella pathogenesis

项目摘要 尽管有现代化的卫生设施和个人卫生，胃肠道感染仍然是一个重大的健康问题， 在美国，失业是一个巨大的经济负担。的一个关键 沙门氏菌致病性的步骤是在肠道中建立定植。当宿主最终清除 沙门氏菌感染后，宿主的初始反应有利于沙门氏菌的生长。同样，一些 肠道细菌促进沙门氏菌肠道定植。例如，这些常驻细菌 否则无法获得的碳源。然而，以前的研究只集中在药物的作用， 细菌在沙门氏菌发病过程中的作用，并没有解决另一个重要的群体， 存在于肠道中的微生物：肠道真菌。近年来，这一研究 微生物群的一个组成部分与包括炎症性肠病在内的多种疾病有关。 然而，肠道真菌在肠道病原体如沙门氏菌的发病机制中的作用尚不清楚。 尽管沙门氏菌编码的基因与肠道真菌高度相互作用， 很有可能。在这方面，沙门氏菌产生真菌和细菌铁载体的三种受体（所谓的铁载体受体）。 异铁载体）。铁载体是由真菌和细菌分泌的用于铁获取的小分子 在低铁环境中，比如发炎的肠道。我们的初步数据显示，两种真菌的表达 铁载体受体赋予沙门氏菌在常规饲养条件下而非无菌条件下的生长优势 小鼠此外，沙门氏菌产生的几丁质酶可以削弱含几丁质的真菌细胞壁， 使沙门氏菌获得真菌营养素，包括细胞内储存的铁载体。因此我们 假设沙门氏菌获得异铁载体，并在 几丁质酶来增加肠道中的定植。我们计划在目标1中研究真菌异铁载体如何 通过消耗或添加真菌促进沙门氏菌在胃肠道中的定植。我们将测序 真菌微生物群来鉴定产生铁载体的真菌。我们还将确定促进生长的效果 第三种异种铁载体受体，它与细菌铁载体结合。在目标2中，我们建议研究如何 微生物群的成员与沙门氏菌竞争异铁载体。为此，我们将减少 微生物群的复杂性。无菌小鼠允许与生产者和竞争者特异性定植， 真菌铁载体我们将测试不产生铁载体的普通真菌和细菌是否能产生铁载体， 如假丝酵母属、酵母属和拟杆菌属与沙门氏菌竞争异铁载体。在目标3中， 将阐明沙门氏菌几丁质酶是否增强沙门氏菌的致病性。我们将测试两个不同的功能， 几丁质酶：削弱真菌细胞壁以获取真菌营养物质，包括细胞内储存的铁载体 以及上皮细胞上粘蛋白或聚糖的降解。我们希望，我们的方法将提高我们的 了解肠道真菌在沙门氏菌感染过程中的作用。在更广泛的背景下，我们预计 我们的工作将有助于设计治疗方法，即肠道病原体的有效竞争者。

PROJECT SUMMARY Despite modern sanitation and hygiene, gastrointestinal infections continue to be a significant health problem in the United States and represent a tremendous economic burden in terms of loss of work. One of the crucial steps of Salmonella pathogenicity is the establishment of colonization in the gut. While the host eventually clears the infection with Salmonella, initial host responses benefit the growth of Salmonella. Similarly, also some commensal bacteria promote Salmonella intestinal colonization. These resident bacteria liberate for example otherwise inaccessible carbon sources. However, previous studies focused exclusively on the role of commensal bacteria during Salmonella pathogenesis and did not address the role of another important group of microorganisms that resides in the gut: commensal intestinal fungi. In recent years, this under-studied component of the microbiota has been implicated in a variety of diseases including Inflammatory Bowel Disease. However, the role of commensal fungi during pathogenesis of gut pathogens like Salmonella is unknown. This is despite the fact that Salmonella encodes genes that make an interaction with commensal gut fungi highly likely. In this regard, Salmonella produces three receptors for fungal and bacterial siderophores (so-called xenosiderophores). Siderophores are small molecules that are secreted by fungi and bacteria for iron acquisition in low iron environments like the inflamed gut. Our preliminary data show that expression of two fungal siderophore receptors confers a growth advantage to Salmonella in conventionally raised but not in germ-free mice. Furthermore, chitinases produced by Salmonella could weaken the chitin-containing fungal cell wall to enable Salmonella to acquire fungal nutrients including intracellularly stored siderophores. We therefore hypothesize that Salmonella acquires xenosiderophores and accesses fungal nutrients with the help of chitinases to increase colonization in the gut. We plan to investigate in Aim 1 how fungal xenosiderophores promote Salmonella colonization in the gastrointestinal tract by depletion or addition of fungi. We will sequence the fungal microbiota to identify siderophore-producing fungi. We will also determine the growth promoting effect of the third xenosiderophore receptor, which binds a bacterial siderophore. In Aim 2, we propose to study how members of the microbiota compete with Salmonella for xenosiderophores. For this, we will reduce the complexity of the microbiota. Germ-free mice allow for specific colonization with producers and competitors for fungal siderophores. We will test if common fungal and bacterial commensals that do not produce siderophores like Candida, Saccharomyces, and Bacteroides compete with Salmonella for xenosiderophores. In Aim 3, we will elucidate if Salmonella chitinases enhance Salmonella pathogenicity. We will test two different functions of chitinases: weakening the fungal cell wall to access fungal nutrients including intracellularly stored siderophores and degradation of mucin or glycans on epithelial cells. We expect that our approaches will enhance our understanding of the role of commensal fungi during infection with Salmonella. In a broader context, we expect our work will help to design treatments, i.e. effective competitors to intestinal pathogens.