Probing the role of commensal intestinal fungi during Salmonella pathogenesis

项目总结 尽管有现代化的卫生设施和个人卫生设施，但在#年胃肠道感染仍然是一个严重的健康问题。 在失业方面，这对美国来说是一个巨大的经济负担。其中一个关键的 沙门氏菌致病的步骤是在肠道内建立定植。当主机最终清除时 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，也有一些 共生菌促进沙门氏菌肠道定植。例如，这些驻留的细菌会释放出 否则就无法获得碳源。然而，以前的研究完全集中在共生的作用上 细菌在沙门氏菌致病过程中的作用并没有涉及到另一类重要的 驻留在肠道中的微生物；共生肠道真菌。近年来，这方面的研究还不够深入 微生物区系的组成部分与包括炎症性肠病在内的各种疾病有关。 然而，共生真菌在沙门氏菌等肠道病原体发病机制中的作用尚不清楚。 这是尽管沙门氏菌编码的基因与共生肠道真菌高度相互作用的事实 很有可能。在这方面，沙门氏菌产生三种真菌和细菌铁载体受体(所谓的 外星铁载体)。铁载体是真菌和细菌分泌的用于获取铁的小分子。 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 铁载体受体使沙门氏菌在常规培养而不是无菌培养中具有生长优势 老鼠。此外，沙门氏菌产生的几丁质酶可以削弱含有几丁质的真菌细胞壁 使沙门氏菌能够获得真菌营养，包括细胞内储存的铁载体。因此，我们 假设沙门氏菌获得外生铁载体并借助 几丁质酶，以增加肠道中的定植。我们计划在目标1中调查真菌异铁生物载体如何 通过消耗或添加真菌来促进沙门氏菌在胃肠道的定植。我们将按顺序排列 真菌微生物区系，用于鉴定产铁载体的真菌。我们还将测定促进生长的效果 第三个外源铁载体受体，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外星铁载体。为此，我们将降低 微生物区系的复杂性。无菌小鼠允许与生产商和竞争对手进行特定的殖民 真菌铁载体。我们将测试不产生铁载体的常见真菌和细菌共生体 与假丝酵母菌一样，酵母菌和类杆菌与沙门氏菌争夺外来铁载体。在目标3中，我们 将阐明沙门氏菌几丁质酶是否增强沙门氏菌的致病性。我们将测试两种不同的功能 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 上皮细胞上粘蛋白或多聚糖的降解。我们希望我们的方法将增强我们的 了解共生真菌在沙门氏菌感染中的作用。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对手。

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.