Complex glycan utilization by human gut Bacteroides

描述（由申请人提供）： 人类肠道微生物群提供了我们自己没有进化的生理属性，包括处理否则难以消化的膳食聚糖的能力。多形拟杆菌{B. Theta）和卵形拟杆菌（Bacteroides ovatus）是微生物群的两个成员，它们具有不同的但仅部分重叠的加工膳食和宿主来源的聚糖的能力-这些聚糖是可能影响它们在拥挤的肠道生态系统中的适应性的进化特征。这些生物体中至少有一种，B。θ，优先考虑植物果胶聚糖的代谢，而不是宿主粘蛋白聚糖，这表明当膳食聚糖丰富时，它已经进化为避免使用宿主粘膜作为营养基础。我将定义和比较这两个物种的碳水化合物利用等级，以确定它们是否进化出相同或不同的优先级。此外，我将探讨B中聚糖优先化的分子机制。theta，让我在gnotobiotic小鼠肠道中测试这种现象的体内适应值。我还将探讨B. ovatus靶向植物细胞壁聚糖的丰富且有时较不可溶的半纤维素类，半纤维素类是一组B。theta不能代谢从B中删除半纤维素利用基因。ovatus基因组，随后是所得的半纤维素缺陷突变体与其同基因亲本的体内竞争，将揭示这些表型的表达是否在喂食富含这些底物的饮食的无菌小鼠中提供适合性优势或劣势。最后，我将探讨聚糖利用表型可以在拟杆菌属物种之间横向转移的可能性，我们的数据表明这种现象是自然发生的。支持这一假设将产生关于微生物群细菌中聚糖利用的基因组进化的基本机制信息。我目前的培训环境，杰弗里戈登在华盛顿大学医学院的实验室，提供了一个独特的地方开始这项研究，可能是世界上唯一的实验室配备了所有必要的工具来回答手头的实验问题。我的职业发展计划包括在戈登实验室建立一个强大的研究基础，并过渡到一个独立的职业生涯作为终身助理教授。在这个指导研究计划中获得的实验和专业培训将为我提供自己成功所需的经验。 公共卫生相关性：人类肠道细菌对于将复杂的膳食多糖转化为我们容易吸收的形式至关重要，其中许多多糖我们自己无法消化。我将描述进入我们饮食的丰富植物聚糖与我们肠道细菌的生理学和进化之间的动态相互关系。研究结果将揭示哪些饮食聚糖细菌“可以”代谢，哪些是他们“想要”代谢的，为我们的肠道微生物群如何收获饮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.