Mutual interactions between the pathobiont Helicobacter hepaticus and the mouse intestinal microbiota: Ecology, mechanisms and relevance to the induction of IBD

原型病原体肝螺杆菌可在免疫功能低下的易感小鼠株中诱发炎症性肠病，肝螺杆菌感染已成为研究IBD发病过程中细菌因素的广泛模型。现有数据表明，肝芽胞杆菌感染引起的病理既取决于细菌的特定致病机制，也取决于肠道微生物群的组成。我们发现，在两个不同的机构（MHH和MIT）饲养的C57BL/6 IL-10小鼠在肝炎感染后对IBD的敏感性非常不同。通过16S rDNA扩增子深度测序（454 FLX技术）对这些小鼠进行微生物群分析，发现了仅存在于一组小鼠中的多种可培养细菌物种，因此可能参与增强或抑制炎症。在项目的第一部分，我们将测试这些单一细菌物种的存在会影响对肝炎杆菌诱导的结肠炎的易感性的假设。将候选菌种添加到微生物群中，然后进行肝芽胞杆菌感染，并分析由此产生的病理和微生物群组成的变化。在第二部分，我们将研究肝炎嗜血杆菌定殖对炎症和非炎症条件下肠道微生物群组成的影响。肝芽胞杆菌基因组包含一个称为HHGI1的致病性岛。这个岛编码6型分泌系统（T6SS），能够将多种蛋白质运送出细菌细胞。先前的研究表明，失去部分岛，或单个基因vgrG1失活，会强烈减弱肝杆菌诱导结肠炎的能力。该项目的另一个目标是了解T6SS功能的丧失如何影响肝芽孢杆菌与微生物群的相互作用。最后，我们将研究在肝芽孢杆菌是复杂微生物群的一部分的情况下，肝芽孢杆菌对小鼠的基因组适应性，并与肝芽孢杆菌单一相关的小鼠进行比较。总之，为了更好地理解模型病原体、肠道微生物群和宿主之间的复杂相互作用，本项目将实验上通用的持续感染模型与最先进的微生物群分析和全基因组比较技术相结合。我们希望在这个项目中获得的发现将被转移到其他epsilon变形菌（例如弯曲杆菌物种）与小鼠和人类生理微生物群之间的相互作用，并有助于理解它们在肠道宿主生态系统中的复杂相互作用，并对其产生积极影响。

The prototype pathobiont, Helicobacter hepaticus, induces inflammatory bowel disease in susceptible immunocompromised mouse strains, and H. hepaticus infection has become a widely used model to investigate bacterial factors involved in IBD pathogenesis. Available data indicate that the pathology induced by H. hepaticus infection depends on both specific pathogenic mechanisms of the bacterium, as well as the composition of the intestinal microbiota. We showed that C57BL/6 IL-10 ko mice reared at two different institutions (MHH and MIT) display very different susceptibilities to IBD after H. hepaticus infection. Microbiota analyses of these mice by deep sequencing of 16S rDNA amplicons (454 FLX technology) have identified multiple culturable bacterial species that are only present in one group of mice and therefore might be involved in augmenting or suppressing inflammation. In a first part of the project, we will test the hypothesis that the presence of these single bacterial species affects susceptibility to H. hepaticus-induced colitis. Candidate species will be added to the microbiota, followed by H. hepaticus infection, and the resulting pathology and shifts in microbiota composition will be analyzed. In a second part, we will investigate the influence of H. hepaticus colonization on the composition of the intestinal microbiota in both inflamed and non-inflamed conditions.The H. hepaticus genome contains a pathogenicity island termed HHGI1. This island encodes a type 6 secretion system (T6SS) capable of transporting multiple proteins out of the bacterial cell. Loss of a part of the island, or inactivation of one single gene, vgrG1, was previously shown to strongly attenuate the ability of H. hepaticus to induce colitis. A further objective of this project is to understand how loss of the T6SS function affects the interaction of H. hepaticus with the microbiota. Finally, we will study the genomic adaptation of H. hepaticus to mice under conditions where H. hepaticus is part of a complex microbiota in comparison with mice that are monoassociated with H. hepaticus. In summary, to better understand the complex interactions between a model pathobiont, the gut microbiota and the host, this project combines an experimentally versatile persistent infection model with state -of-the-art microbiota analysis and whole genome comparison technology. We hope that findings obtained during this project will be transferable to interactions between other epsilon proteobacteria (e.g. Campylobacter species) and the physiological microbiota in mice and humans, and to contribute to understanding their complex interplay within the intestinal host ecosystem, and to positively influence it.