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

肝幽门螺杆菌的原型致病株可在免疫功能低下的小鼠中诱发炎症性肠病，肝螺杆菌感染已成为研究IBD发病机制中细菌因素的广泛应用模型。现有资料表明，肝片吸虫感染的病理机制既取决于细菌的特定致病机制，也取决于肠道微生物区系的组成。我们发现，在两个不同机构(MHH和MIT)饲养的C57BL/6 IL-10 Ko小鼠在感染肝吸虫后表现出非常不同的IBD易感性。通过对16S rDNA扩增片段的深度测序(454 FLX技术)对这些小鼠进行的微生物区系分析发现了多种可培养的细菌物种，这些细菌只存在于一组小鼠中，因此可能参与增强或抑制炎症。在项目的第一部分，我们将测试这一假设，即这些单一细菌物种的存在会影响对肝炎性结肠炎的易感性。候选物种将被添加到微生物区系中，随后是肝片吸虫感染，并将分析由此产生的病理和微生物区系组成的变化。在第二部分中，我们将研究在炎症和非炎症条件下，肝片吸虫定植对肠道微生物区系组成的影响。这个岛编码一个6型分泌系统(T6SS)，能够将多种蛋白质输送出细菌细胞。岛的一部分丢失，或单个基因vgrG1的失活，以前被证明会强烈减弱肝炎螺旋体诱导结肠炎的能力。该项目的另一个目标是了解T6SS功能的丧失如何影响肝炎杆菌与微生物区系的相互作用。最后，我们将研究在肝片吸虫是复杂微生物群的一部分的条件下，与与肝片吸虫单一相关的小鼠相比，肝片吸虫对小鼠的基因组适应性。总之，为了更好地了解模型病原体、肠道微生物区系和宿主之间的复杂相互作用，该项目将一个实验通用的持续感染模型与最先进的微生物区系分析和全基因组比较技术相结合。我们希望在这个项目中所获得的发现将被应用于其他Esilon蛋白细菌(如弯曲杆菌)与小鼠和人类的生理微生物群之间的相互作用，并有助于了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.