Understanding how heme and iron are metabolized by anaerobic commensal bacteria and host-microbiome communities

项目摘要 关于消化道中流行的细菌（其中大多数是厌氧菌）如何摄取和消化道中的蛋白质， 处理宿主的膳食铁。这种活动如何影响铁被吸收的效率， 主持人也不清楚。缩小这一知识差距既具有根本意义，也具有生物医学意义。铁- 缺乏症和相关贫血是全世界最普遍的营养失调， 三分之一的人口。与此同时，来自红肉饮食的未代谢血红素铁仍然存在于 结肠与从炎症到结肠癌的疾病的发展有关， 其中微生物活动被认为起着关键作用。这项工作的长期目标是了解如何 在健康哺乳动物肠道中常见的细菌在低/无铁条件下代谢铁。 在这个生态系统中普遍存在的氧气条件。拟议的工作集中了我们小组的知识， 基础设施-积累了超过15年的研究有氧血红素/铁生物化学在催化剂的水平， 细胞和生态系统-这个雄心勃勃的长期目标，我们已经分为两个重叠的部分。 首先，我们将研究常见的肠道微生物，其中大多数是厌氧的，血红素营养缺陷型 细菌（HAB）代谢血红素。我们集中研究三种实验上容易处理的有害藻华， 在人类中大量存在，并且需要血红素进行呼吸（多形拟杆菌）， 属于但不依赖于血红素介导的呼吸作用（鼠李糖乳杆菌），或专性发酵 但对于血红素（梭菌属（Clostridium））仍具有有限的用途。我们将研究基因（通过产生 敲除）和被预测在这些物种的血红素代谢中起重要作用的基因产物， 但属于通常不完全的代谢途径。与此同时，我们将聘请 以发现为基础的方法来确定血红素蛋白质组的成员，使用化学定义的生长 媒体，稳定同位素标记的血红素，和光谱分析，我们有深入的专业知识。 其次，我们将确定肠道细菌物种如何共同工作，并与动物宿主代谢 血红素铁作为我们实验方法的一部分，我们将使用敲除菌株和同位素标记的血红素 使用上述三种HAB的子集和常见的肠道菌，通过共培养来检查血红素代谢 血红素异养菌（大肠杆菌）。将在培养瓶中和小鼠中研究共培养物， （gnotobiotic）微生物组，与Seth Walk教授（MSU）合作。了解厌氧血红素 微生物的代谢服务于操纵微生物组的长期生物医学目标， 促进铁的宿主代谢，从而治疗与缺铁（贫血）相关的疾病，或 过量（感染、结肠炎、炎症、结肠癌）。

PROJECT SUMMARY Little is known about how bacteria prevalent in the digestive tract, most of which are anaerobes, take up and process the host’s dietary iron. How this activity influences the efficiency with which iron is absorbed by the host is also unclear. Closing this gap in the knowledge is of both fundamental and biomedical interest. Iron- deficiency and associated anemia are the most prevalent nutritional disorders worldwide, shared by nearly a third of the human population. At the same time, unmetabolized heme iron from red meat diets that remains in the colon has been associated with the development of diseases ranging from inflammation to colon cancer, with microbial activity postulated to play a key role. The long-term goal of this work is to understand how commensal bacteria commonly found in the healthy mammalian gut metabolize iron under the low/no O2 conditions that are prevalent in this ecosystem. The proposed work focuses our group’s knowledge and infrastructure – accrued over 15 years of studying aerobic heme/iron biochemistry at the level of the catalyst, cell, and ecosystem – on this ambitious long-term goal, which we have divided into two overlapping parts. First, we will examine how common gut microbes, most of which are anaerobic, heme auxotrophic bacteria (HAB), metabolize heme. We are focusing on three experimentally tractable HAB which are abundant in humans and which either require heme for respiration (Bacteroides thetaiotaomicron), are capable of but not dependent on heme-mediated respiration (Lactobacillus rhamnosus), or are obligately fermentative but still have limited uses for heme (Clostridium scindens). We will examine genes (via the generation of knock-outs) and gene products that are predicted to play important roles in heme metabolism in these species, but which belong to metabolic pathways that are typically incomplete. At the same time, we will employ discovery-based approaches to identify members of the heme-proteome, using chemically defined growth media, stable-isotope-labeled heme, and spectroscopic analyses with which we have a depth of expertise. Second, we will define how gut bacterial species work together and with the animal host to metabolize heme iron. As part of our experimental approach, we will use knock-out strains and isotopically labeled heme to examine heme metabolism by co-cultures, using subsets of the three HAB above and a common enteric heme heterotroph (Escherichia coli). Cocultures will be studied both in the flask and in mice with defined (gnotobiotic) microbiomes, in collaboration with Prof. Seth Walk (MSU). Understanding anaerobic heme metabolism by commensal bacteria serves the long-term biomedical goal of manipulating the microbiome to facilitate host metabolism of iron, thereby remediating diseases associated with iron deficiency (anemia) or excess (infection, colitis, inflammation, colon cancer).