The Role of Type VI Secretion in Cholera Pathogenesis

项目摘要/总结 我们对霍乱弧菌的特定谱系如何引起霍乱暴发的理解存在差距， 小肠感染，引发严重的水泻、脱水，并经常导致死亡。霍乱 在世界许多地区流行，每年造成超过120，000人死亡。霍乱也是最早的 当医疗保健系统和卫生基础设施在经济危机期间崩溃时， 或者是国内危机，就像最近在也门发生的50万起病例和2,000人死亡。 这一建议的科学前提是长期以来的认识，即霍乱疫情出现在单一的 克隆谱系-基因上密切相关的菌株。虽然它的自然水生环境 不同的霍乱弧菌种群，既有致病性（产生霍乱毒素的主要毒力因子， 毒素协同调节菌毛）和非致突变菌株，霍乱暴发是由单克隆谱系引起的。 我们认为，产酶菌株使用VI型分泌系统（T6 SS）作为一种主动竞争机制 以防止其他菌株在小肠内定植。T6 SS在结构上类似于注射器， T4噬菌体的细胞器，并将有毒的T6 SS效应物递送到邻近的细菌中。效应器的递送是 致命的，除非接收细胞产生免疫蛋白，隔离传入的毒素。 T6 SS在染色体上的三个不同的基因座中编码。每个位点都有一个水平获得的遗传基因 一个具有独特的毒素免疫对的元素，称为模块。一个菌株中的三个效应器模块一起 包括其效应器模块组（例如，AAA-模块组用于产酶菌株）。我们发现， 相同的模块是相容和共存的，而具有不同模块的菌株在接触时竞争。 我们的中心假设是，致炎性霍乱弧菌获得了最具竞争力的T6 SS模块集（AAA）， 排除不相容的作弊菌株。为了检验我们对资助父母补助金的假设，我们将解决 获得AAA模块集（目的I），如何在体内使用（目的II）以及如何有助于克隆优势 (Aim III）。在这个修订后的提案中，我们增加了一个子目标（目标IIIb），以测试AAA菌株何时何地成为 在孟加拉国接触霍乱的人群中占主导地位。 该提案研究了细菌竞争机制如何有助于爆发的克隆性质， 使我们能够利用策略来干扰致病谱系的能力，以扩大和引起霍乱。

PROJECT ABSTRACT/SUMMARY There is a gap in our understanding of how specific lineages of Vibrio cholerae cause outbreaks of cholera - an infection of the small intestine that triggers severe watery diarrhea, dehydration, and, too often, death. Cholera is endemic in many regions of the world, causing over 120,000 deaths every year. Cholera is also one of the first diseases to emerge when the health care system and sanitation infrastructure break down during an economic or civil crisis, as witnessed just recently in Yemen with 500,000 cases and 2,000 deaths. The scientific premise for this proposal is a longstanding appreciation that cholera outbreaks emerge from single clonal lineages – strains that are closely related genetically. Although its natural aquatic environment harbors a diverse V. cholerae population, with both toxigenic (producing the main virulence factors of cholera toxin and toxin-coregulated pilus) and non-toxigenic strains, cholera outbreaks are caused by single clonal lineages. We propose that toxigenic strains use the type VI secretion system (T6SS) as an active competition mechanism to prevent other strains from colonizing the small intestine. The T6SS structurally resembles the injection apparatus of T4 bacteriophage and delivers toxic T6SS effectors into adjacent bacteria. Delivery of effectors is lethal unless the receiving cell produces immunity proteins that sequester the incoming toxins. The T6SS is encoded in three distinct loci on the chromosome. Each locus hosts a horizontally acquired genetic element with a distinct toxin–immunity pair called a module. Together, the three effector modules in a strain comprise its effector module set (e.g., AAA-module set for toxigenic strains). We discovered that strains with identical modules are compatible and co-exist, while strains with different modules compete on contact. Our central hypothesis is that toxigenic V. cholerae acquired the most competitive T6SS module set (AAA) to exclude incompatible cheater strains. To test our hypothesis for the funded parent grant, we will resolve how the AAA module set is acquired (Aim I), how it is used in vivo (Aim II) and how it contributes to clonal dominance (Aim III). In this revised proposal, we are adding a sub-aim (Aim IIIb) to test when and where AAA strains become dominant in human populations in Bangladesh exposed to cholera. This proposal investigates how bacterial competition mechanisms contribute to the clonal nature of outbreaks, allowing us to exploit strategies that interfere with the ability of toxigenic lineages to expand and cause cholera.