COLLABORATIVE RESEARCH: Environmental and internal influences on the activities of the Calvin- and reductive citric acid cycles in hydrothermal vent symbiosis Riftia pachyptila

地球上的所有生命都依赖于有机体将二氧化碳固定为有机碳，这些有机体用光能或高能化学物质为这一过程提供动力。有四种已知的催化碳固定的途径。基于系统发育分布和功能属性，有人假设在植物、藻类和一些细菌中发现的Calvin Benson Bassham循环，由于其对氧气的适应能力，在有氧陆地和海洋有氧栖息地中占主导地位，而其他“氧敏感”的碳固定途径则被转移到缺氧或缺氧的环境中，如喷口和温泉。与这一假设相反，在热液喷口周围的缺氧弥散流动中发现了共生现象，其中细菌伴侣使用卡尔文·本森·巴萨姆循环。管虫-细菌共生，特别是厚皮裂谷菌（“裂谷菌”），是太平洋热液喷口的主要关键物种。这些共生系统固定碳的质量比速率与生长最快的植物相当。令人惊讶的是，最近的研究表明，细菌共生体使用两种碳固定途径，卡尔文本森巴萨姆循环和还原性三羧酸循环。单一生物（细菌）使用这两种途径来固定碳是前所未有的，可能是一种应对热液喷口生物遇到的环境条件高度变化的策略。在这里提出的工作中，Riftia将在高压水族箱中孵育，条件模仿原位环境变化。对细菌和管虫宿主的生化分析将用于确定环境条件、代谢活动和两种途径的不同使用之间的关系，以了解它们如何协同作用以维持动态环境中的碳固定。这些数据将大大进一步了解环境对细菌和植物固碳的影响，也将有助于确定为什么不同的生物具有不同的固碳途径。我们同样致力于拟议的科学研究和我们拟议的教育和推广。我们计划支持三个主要项目：(1)研究生发展；(2)本科生指导；(3)使用真实研究数据和经验设计高影响力的教育课程。本研究将支持和训练本科生和研究生，他们将密切参与实验的设计和工程，分析数据，并正式展示和记录工作。拟议的研究包含重要的领域和实验室组成部分，这为学生和教师提供了在不同层次上参与该项目的机会。

All life on Earth depends upon the fixation of carbon dioxide to organic carbon by organisms that power this process with light energy or high-energy chemicals. There are four known pathways that catalyze carbon fixation. Based on phylogenetic distributions and functional attributes, it has been posited that the Calvin Benson Bassham cycle, found in plants, algae, and some bacteria, dominates in aerobic terrestrial and marine aerobic habitats due to its resilience to oxygen, while other 'oxygen sensitive' carbon fixation pathways are relegated to hypoxic or anoxic environs like vents and hot springs. Contrary to this supposition, there are symbioses found in hypoxic diffuse flows around hydrothermal vents in which the bacterial partner uses the Calvin Benson Bassham cycle. Tubeworm-bacterial symbioses, in particular Riftia pachyptila ("Riftia"), are the dominant keystone species at hydrothermal vents in the Pacific Ocean. These symbiotic systems fix carbon at mass specific rates comparable to the fastest growing plants. Surprisingly, recent studies suggest that the bacterial symbionts use two carbon fixation pathways, the Calvin Benson Bassham cycle and the reductive tricarboxylic acid cycle. The use of these two pathways by a single organism (the bacterium) to fix carbon is unprecedented, and may be a strategy to cope with the high variability in environmental conditions encountered by hydrothermal vent organisms. For the work proposed here, Riftia will be incubated in high-pressure aquaria under conditions that mimic the environmental variations found in situ. Biochemical assays on the bacteria and tubeworm host will be used to ascertain the relationship between environmental conditions, metabolic activity and differential use of the two pathways, to understand how they act in concert to sustain carbon fixation in a dynamic environment. These data will considerably further the understanding of the influence of environment on carbon fixation by bacteria as well as plants, and will also be helpful for determining why different organisms have the different carbon fixing pathways.We are equally committed to the proposed scientific research and our proposed education and outreach. We plan to support three major programs: (1) graduate student development (2) undergraduate mentoring, and (3) the design of high-impact educational curricula using real research data and experiences. This study will enable the support and training of undergraduate and graduate students who will be intimately involved in designing and engineering the experiments, analyzing the data, and formally presenting and documenting the work. The proposed research contains significant field and laboratory components, which affords students and teachers the opportunities to participate in this project at a variety of levels.