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

项目总结 关于消化道中流行的细菌(其中大部分是厌氧菌)是如何吸收和 加工寄主的膳食铁。这种活动如何影响人体吸收铁的效率 主办方也不清楚。缩小这一知识差距既是基本的，也是生物医学的利益所在。铁- 营养缺乏症和相关的贫血是世界上最普遍的营养失调，有近1/3的人患有此病。 占总人口的三分之一。同时，红肉中残留的未代谢的血红素铁 从炎症到结肠癌，结肠一直与各种疾病的发展有关， 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 健康哺乳动物肠道中常见的共生细菌在低/一氧化氮条件下代谢铁 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和 基础设施-在催化剂水平上研究好氧血红素/铁生物化学15年来积累的经验， 细胞和生态系统--关于这个雄心勃勃的长期目标，我们将其分为两个重叠的部分。 首先，我们将研究常见的肠道微生物，其中大部分是厌氧、血红素营养缺乏症。 细菌(HAB)，代谢血红素。我们将重点放在三个实验上容易处理的HAB上，它们是 在人类中大量存在，它们要么需要血红素进行呼吸(拟杆菌)，要么能够 属于但不依赖于血红素介导的呼吸(鼠李糖乳杆菌)，或必须发酵的 但对血红素(斯氏梭菌)的用途仍然有限。我们将检查基因(通过生成 基因敲除)和基因产物被预测在这些物种的血红素代谢中发挥重要作用， 但它们属于通常不完整的新陈代谢途径。同时，我们将聘请 使用化学定义的生长识别血红素蛋白质组成员的基于发现的方法 媒体，稳定同位素标记的血红素，和光谱分析，我们在这方面有很深的专业知识。 其次，我们将定义肠道细菌如何与动物宿主一起代谢。 亚铁血红素。作为我们实验方法的一部分，我们将使用基因敲除菌株和同位素标记的血红素 使用上述三种HAB的亚群和一种常见的肠道细菌，通过共培养来检查血红素的代谢 血红素异养菌(大肠杆菌)。混合培养将在烧瓶中进行研究，并在小鼠身上进行 (诺生菌)微生物群，与塞斯·沃克教授(密歇根州立大学)合作。对厌氧血红素的认识 共生细菌的新陈代谢服务于长期的生物医学目标，即操纵微生物组以 促进宿主铁的新陈代谢，从而治疗与缺铁(贫血)或 过度(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).