The Role of Type VI Secretion in Cholera Pathogenesis

项目摘要/摘要 我们对霍乱弧菌特定谱系如何导致霍乱暴发的理解存在差距 小肠感染，引起严重的水样腹泻、脱水，常常导致死亡。霍乱 该病在世界许多地区流行，每年造成超过12万人死亡。霍乱也是首批 当医疗保健系统和卫生基础设施在经济衰退期间崩溃时，疾病就会出现 或国内危机，就像最近在也门发生的50万起病例和2 000人死亡一样。 这一提议的科学前提是一个长期存在的认识，即霍乱暴发是由一个 克隆谱系--在遗传上密切相关的菌株。尽管它的自然水生环境蕴藏着 霍乱弧菌种群多样，既有产毒(产生霍乱毒素的主要毒力因子)，也有 霍乱暴发是由单一克隆谱系引起的，它们是由毒素共调节菌毛)和非产毒菌株引起的。 我们认为产毒菌株使用VI型分泌系统(T6SS)作为一种主动竞争机制 以防止其他菌株侵占小肠。T6SS在结构上类似于注射器 T4噬菌体的装置，并将有毒的T6SS效应物输送到邻近的细菌中。效应器的交付是 致命性的，除非接收细胞产生免疫蛋白来隔离传入的毒素。 T6SS编码在染色体上的三个不同的位置。每个基因座都有一个水平获得性基因 元素具有不同的毒素-免疫对，称为模块。加在一起，三个效应器模块处于应变状态 包括其效应器模组(例如，用于产毒菌株的AAA模组)。我们发现菌株与 相同的模块是兼容和共存的，而不同模块的菌株在接触时竞争。 我们的中心假设是，产毒霍乱弧菌获得了最具竞争力的T6SS模块集(AAA)来 排除不相容的作弊菌株。为了测试我们的假设，我们将解析如何获取AAA模块集 (目标一)、如何在体内使用(目标二)以及如何促成克隆优势(目标三)。 这项建议调查了细菌竞争机制如何有助于疫情的克隆性， 使我们能够利用干扰产毒血统扩大并导致霍乱的能力的策略。

PROJECT SUMMARY/ABSTRACT 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, 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). 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.