Each day massive quantities of wood and woody plant materials enter the oceans, providing resources upon which a large variety of marine organisms depend. However, the biological communities supported by marine wood are only poorly understood. Globally, the most important consumers of marine wood are wood-boring bivalves of the family Teredinidae (shipworms, primarily found above 150 m) and Pholadidae (subfamily Xylophagainae, primarily found in the deep sea, 150-8000 m). These clams depend on intracellular endosymbiotic bacteria (endocytobionts) to help them consume a substrate (lignocellulose) that cannot be utilized by most other animals. Two functions have been proposed for symbionts of wood-boring bivalves; 1) production of enzymes to facilitate lignocellulose digestion (xylotrophy) and 2) nitrogen fixation (diazotrophy) to supplement the host.s nitrogen-deficient diet. The purpose of the proposed research is to explore the physiological ecology of symbiotic xylotrophy in shipworms using molecular, biochemical and microbiological techniques. Three questions are foremost in this investigation; 1) What genetic variation occurs in symbiont populations within and between host species? 2) What is the quantitative contribution of symbionts to lignocellulose digestion and nitrogen fixation? and 3) What physical and biochemical mechanisms are involved in transfer of nutrients and enzymes between host and symbiont compartments?
