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.
