Ammonia Assimilation in the Chemoautotrophic Bacteria-Clam Symbiosis Solemya Velum

与化学自养细菌的共生使一些海洋无脊椎动物，如蛤蜊、贻贝和管虫，能够不依赖颗粒食物来获取营养而生存。相反，这些生物是自养的。它们能够利用硫化氢作为能源，通过类似于植物光合作用的过程，将二氧化碳和氨固定成有机化合物。自养的许多生化途径都局限于寄主组织特化细胞内的细胞内共生体。因此，这些无脊椎动物在其他不适宜居住或食物匮乏的环境中茁壮成长，如深海热液喷口、冷渗漏和厌氧沉积物。该项目的目标是确定导致自养代谢的生理和生化机制。该项目将涉及一种容易收集的沿海蛤共生，Solemya velum。以前的研究主要是针对难以在实验室收集和饲养的动物。实验将集中于氨同化为有机化合物，并解决具体问题，包括：什么是S. velum的氨吸收能力，氨吸收如何受到环境条件的影响，什么生化途径负责同化，这些途径是否局限于宿主或共生体？这些问题将使用生物化学和分子技术的结合，以及使用新设计的自动流式呼吸测量系统进行全生物体生理学研究。基于共生的自养是一个全球性的重要过程，可以支持整个生态系统，如深海喷口或珊瑚礁。这一过程是由宿主/共生体相互作用产生的，而这种相互作用在这些和许多其他共生体系统中尚未得到很好的理解。更好地了解这些相互作用的性质以及它们如何影响整个关联的特征和生理，对于保护和管理依赖共生生物的生态系统是有价值的。这一信息可能具有更广泛的影响，因为细菌（互惠和寄生）与其他生物体的联系无处不在。

Symbiosis with chemoautotrophic bacteria enables some marine invertebrates, such as clams, mussels, and tubeworms, to live without relying on particulate food for their nutrition. Instead, these organisms are autotrophic. They are able to fix carbon dioxide and ammonia into organic compounds using hydrogen sulfide as an energy source via a process analogous to photosynthesis in plants. Many of the biochemical pathways of autotrophy are localized to intracellular symbionts housed within specialized cells of the host tissues. Consequently, these invertebrates thrive in otherwise inhospitable or food-poor environments such as deep-sea hydrothermal vents, cold seeps, and anaerobic sediments. The goal of this project is to determine the physiological and biochemical mechanisms that result in autotrophic metabolism. This project will involve a readily collected coastal clam symbiosis, Solemya velum. Previous studies have largely been of animals that are difficult to collect and maintain in the laboratory. Experiments will focus on assimilation of ammonia into organic compounds and address specific questions including: what are the ammonia uptake capabilities of S. velum, how is ammonia uptake affected by environmental conditions, what biochemical pathways are responsible for assimilation, and are these pathways localized to the host or symbiont? These questions will be investigated using a combination of biochemical and molecular techniques as well as whole organism physiological studies using a newly designed automated flow-through respirometry system. Symbiosis-based autotrophy is a globally important process that can support entire ecosystems such as deep-sea vents or coral reefs. This process results from mutualistic host/symbiont interactions that are not well understood in these and many other symbiotic systems. A better understanding of the nature of these interactions and how they affect the characteristics and physiology of the association as a whole can be valuable in preserving and managing ecosystems that rely on symbiotic organisms. This information potentially has even broader impacts, since association of bacteria (mutualistic and parasitic) with other organisms are ubiquitous.