Physiological Role and Phylogenetic Diversity of Termite Gut Symbionts

白蚁肠道共生体的生理作用和系统发育多样性

• 批准号: 0114505
• 负责人: John Breznak
• 金额: $ 78.2万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0114505&HistoricalAwards=false
• 关键词: Physiological; Role; Phylogenetic; Diversity; Termite

IBN-0114505: Physiological Role and Phylogenetic Diversity of Termite Gut SymbiontsPrincipal Investigator: John A. Breznak, Michigan State UniversityTermites are important decomposers of earth's major form of biomass -- lignocellulosic plant material and residues derived from it, e.g. humus. In order to thrive on such relatively refractory, nitrogen-poor food resources, termites are aided by a diverse community of gut microbial symbionts. The nature of the gut microbes, and their role in termite nutrition and vitality, has been an ongoing focus of research in the PI's laboratory for many years. Research supported by the current award is largely an outgrowth of a breakthrough, which led to two major discoveries during the previous funding period. The breakthrough was the isolation in pure culture of a long-recognized, major, and morphologically distinct, but hitherto elusive, component of the termite gut microbial community, i.e. spirochetes. The discoveries were: (a) the recognition of them as novel species of Treponema capable of acetate production from a variety of substrates, including H2+CO2; and (b) the demonstration of nitrogenase structural genes (nifH) and N2 fixation in these (and subsequently in free-living) spirochetes. Inasmuch as microbially-produced acetate supports up to 100% of the daily energy requirement of termites, and N2 fixation by gut microbes can supply up to 60% of the nitrogen for termite growth, the importance of spirochetes in termite nutrition was becoming clearer. Moreover, as neither H2/CO2-acetogenesis nor N2 fixation had ever been recognized in spirochetes before, these discoveries were also providing new insight into the metabolic diversity of these fascinating bacteria.A combination of physiological, biochemical, and molecular biological methods will now be used to explore these metabolic activities in greater detail. We seek to identify factors affecting their expression and activity, and to assess the importance of spirochetes to H2/CO2-acetogenesis and N2 fixation in situ. Cooperative and antagonistic interactions of spirochetes with other members of the gut microbiota will also be examined, including: the provision of folate compounds (required for growth of termite gut spirochetes) by other gut microbes that utilize spirochete products, e.g. acetate oxidizers; and antagonisms between H2/CO2-acetogenic spirochetes and H2-consuming methanogens - two groups of microbes competing for the same energy source. Studies will also be done to test the hypothesis that many of the (non-spirochetal) gut microbes colonizing the microoxic region of hindguts near the epithelium are microaerophiles that have previously escaped isolation in pure culture, because they will not grow in air or under anoxia. It is hypothesized that such microaerophiles are acetate-oxidizers that consume inwardly diffusing O2, thereby rendering the luminal region of the gut anoxic for the fermentative production (by spirochetes and protozoa) of more acetate. This latter effort is likely to reveal new principles about life under hypoxia, a pervasive but poorly studied condition experienced by many organisms in our biosphere. This research project will involve graduate students and a postdoctoral and, hence, will expand the base of scientists trained to explore two of the most salient features of the microbial world - its enormous, but poorly understood and largely untapped diversity, and its importance to macrobial life on our planet.

IBN-0114505：白蚁肠道共生体的生理作用和系统发育多样性。Breznak，密歇根州立大学白蚁是地球上主要形式的生物质的重要分解者-木质纤维素植物材料及其残留物，例如腐殖质。为了在这种相对难处理的、氮缺乏的食物资源上茁壮成长，白蚁得到了多种肠道微生物共生体的帮助。肠道微生物的性质，以及它们在白蚁营养和活力中的作用，多年来一直是PI实验室的研究重点。该奖项支持的研究主要是一项突破的结果，该突破在上一个资助期内导致了两项重大发现。突破是在纯培养物中分离出白蚁肠道微生物群落的一种长期公认的、主要的、形态上不同的、但迄今为止难以捉摸的组分，即螺旋体。这些发现是：（a）确认它们为能够从多种底物（包括H2+CO2）产生乙酸盐的密螺旋体的新物种;和（B）证明在这些螺旋体中（以及随后在自由生活的螺旋体中）存在固氮酶结构基因（nifH）和N2固定。由于微生物产生的乙酸盐支持白蚁高达100%的日常能量需求，肠道微生物的N2固定可以为白蚁生长提供高达60%的氮，螺旋体在白蚁营养中的重要性变得越来越清楚。此外，由于螺旋体的H2/CO2-产乙酸和N2固定功能在以往的研究中均未被发现，这些发现也为螺旋体代谢多样性的研究提供了新的视角，将结合生理学、生物化学和分子生物学方法对这些代谢活动进行更详细的研究。我们试图确定影响其表达和活性的因素，并评估螺旋体的重要性，H2/CO2-乙酸和N2固定原位。还将检查螺旋体与肠道微生物群的其他成员的合作和拮抗相互作用，包括：利用螺旋体产物的其他肠道微生物提供叶酸化合物（白蚁肠道螺旋体生长所需），例如乙酸氧化剂;和H2/CO2产乙酸螺旋体和H2消耗产甲烷菌之间的拮抗作用-两组微生物竞争相同的能源。还将进行研究以检验以下假设：定殖在后肠上皮附近的微氧区域的许多（非螺旋体）肠道微生物是先前在纯培养物中逃脱分离的微需氧菌，因为它们不会在空气中或缺氧下生长。据推测，这种微需氧菌是乙酸盐氧化剂，消耗向内扩散的O2，从而使肠腔区域缺氧，用于发酵生产（通过螺旋体和原生动物）更多的乙酸盐。后一种努力可能揭示缺氧下生命的新原理，缺氧是我们生物圈中许多生物体经历的普遍但研究不足的条件。这个研究项目将涉及研究生和博士后，因此，将扩大科学家的基础，他们经过培训，探索微生物世界的两个最显著的特征-其巨大的，但知之甚少，基本上未开发的多样性，以及其对我们星球上的宏生物生命的重要性。