This research investigates the metabolic interplay between an invertebrate host and its symbiotic, sulfur-oxidizing bacteria by studying (1) the role of sulfur compounds in maintaining the functional symbiosis, (2) the internal defense mechanisms used for detoxifying sulfide, and (3) the role of sulfur compounds in supporting ATP synthesis, carbon fixation, and cellular metabolic rate. The bivalve host Lucinia floridana harbors high densities of chemoautotrophic bacteria in its gill tissues, and furthermore, the bacteria are invariably housed in one specific typed of eucaryotic cell, the bacteriocyte. The use of isolated bacteriocytes figures prominently in the experimental approach, because this cell type represents the simplest level of organization at which the symbiosis is defined. Studies of sulfide detoxification will be conducted at three levels of biological organization: tissue, isolated cells, and isolated organelles. This multi-level approach should allow accurate resolution of the functional contributions to chemical defense of all individual components and then to integrated these separate mechanisms into a unified model for sulfide detoxification in this organism.
