Complex glycan utilization by human gut Bacteroides

描述(由申请人提供)： 人类肠道微生物区系提供了我们不必自己进化的生理属性，包括处理原本无法消化的饮食多糖的能力。Thetaiotaomicron(B.theta)和Bacteroidesovatus是微生物群中的两个成员，它们处理食物和宿主衍生的多糖的能力不同，但只有部分重叠-这些进化特征可能会影响它们在拥挤的肠道生态系统中的适合性。在这些生物中，至少有一种叫B.theta，它优先考虑植物果胶多糖的新陈代谢，而不是宿主粘蛋白多糖，这表明当饮食中的多糖丰富时，它已经进化到避免使用宿主粘膜作为营养基础。我将定义并比较这两个物种的碳水化合物利用等级，以确定他们进化出的优先顺序是相同的还是不同的。此外，我将探索在B.theta中多糖优先排列的分子机制，使我能够在体内测试这一现象在灵生小鼠肠道中的适合性价值。我还将探索卵形芽孢杆菌针对植物细胞壁多糖的机制，半纤维素含量丰富，有时不易溶解，这是一组B.theta不能代谢的底物。从卵形芽孢杆菌基因组中删除半纤维素利用基因，然后在体内与其同基因双亲竞争产生的半纤维素缺陷突变体，将揭示这些表型的表达在喂养富含这些底物的GnotoBiotic小鼠中是否提供了适合的优势或劣势。最后，我将探索利用多糖的表型在类杆菌属物种之间横向转移的可能性，我们的数据表明这一现象是自然发生的。这一假说的支持将产生有关微生物区系细菌间利用多糖的基因组进化的基本机制信息。我目前的培训环境是华盛顿大学医学院的杰弗里·戈登的实验室，它为开始这项研究提供了一个独特的地方，也可能是世界上唯一一个配备了回答手头实验问题的所有必要工具的实验室。我的职业发展计划包括在戈登实验室建立一个坚实的研究基础，并过渡到一个独立的职业生涯，成为终身教职的助理教授。在这个指导性的研究方案中获得的实验和专业培训将为我提供独立取得成功所需的经验。 与公共卫生相关：人体肠道细菌对于将复杂的饮食多糖转化为我们容易吸收的形式至关重要，其中许多我们自己无法消化。我将描述大量进入我们饮食的植物多糖与我们肠道细菌的生理和进化之间的动态相互关系。研究结果将揭示细菌“能”代谢哪些膳食糖链，以及它们“想”代谢哪些糖链，从而为我们的肠道微生物区系如何获取膳食营养提供新的知识。

DESCRIPTION (provided by applicant): The human gut microbiota provides physiologic attributes that we have not had to evolve on our own, including the ability to process otherwise indigestible dietary glycans. Bacteroides thetaiotaomicron {B. theta) and Bacteroides ovatus, two members of the microbiota, have diverse but only partially overlapping abilities to process dietary and host-derived glycans - evolved features that likely influence their fitness in the crowded gut ecosystem. At least one of these organisms, B. theta, prioritizes metabolism of plant pectic glycans over host mucin glycans, suggesting that it has evolved to avoid using the host mucosa as a nutrient base when dietary glycans are abundant. I will define and compare the carbohydrate utilization hierarchies of these two species to determine if they evolved the same or different priorities. Moreover, I will explore the molecular mechanisms that underlie glycan prioritization in B. theta, allowing me to test the fitness value of this phenomenon in vivo in the gnotobiotic mouse gut. I will also explore the mechanisms through which B. ovatus targets the abundant and sometimes less soluble hemicellulose class of plant cell wall glycans, a group of substrates that B. theta is not able to metabolize. Deletion of hemicellulose utilization genes from the B. ovatus genome followed by in vivo competition of the resulting hemicellulose-deficient mutants with their isogenic parents, will reveal if expression of these phenotypes provides a fitness advantage or disadvantage in gnotobiotic mice fed a diet rich in these substrates. Finally, I will explore the possibility that glycan utilization phenotypes can be laterally transferred between Bacteroides species, a phenomenon that our data suggest occurs naturally. Support of this hypothesis will yield fundamental mechanistic information about genomic evolution of glycan utilization among microbiota bacteria. My current training environment, Jeffrey Gordon's lab at Washington University Medical School, provides a unique place to begin this research and may be the only lab in the world equipped with all of the necessary tools to answer the experimental questions at hand. My career development plan includes building a robust research foundation in the Gordon lab and transitioning into an independent career as a tenure track Assistant Professor. The experimental and professional training achieved during this mentored research proposal will provide the experience I need to be successful on my own. PUBLIC HEALTH RELEVANCE: Human gut bacteria are essential for the transformation of complex dietary polysaccharides, many of which we cannot digest on our own, into forms that we readily absorb. I will characterize the dynamic interrelationships between abundant plant glycans that enter our diets and the physiology and evolution of our gut bacteria. The results will reveal which dietary glycans bacteria 'can' metabolize and which ones they 'want' to metabolize, providing new knowledge about how our gut microbiota harvests dietary nutrients.