This proposal addresses one of the most elusive problems in marine bacterial symbiosis research: that of the mode and mechanisms of symbiont inheritance. Our recent rDNA/rRNA-based hybridization probe studies have demonstrated the efficacy of these techniques in resolving low copies of symbiont target within host tissues. A trans-ovarial mechanism of symbiont transmission has now been identified in several species of deep-sea Vesicomyid clams, however the developmental process of symbiont incorporation cannot be elucidated in these deep-sea representatives. With initial studies completed we propose to employ a similar suite of molecular tools with several novel additions to examine the ontogenetic and biochemical process of bacterial symbiont incorporation in the protobranch bivalve Someya reidi. Specifically we will: 1) determine the mode of symbiont transmission and ontogenetic process of incorporation into the gill tissue, 2) to may the metabolic state of the symbionts during the incorporation process and determine the role of the symbionts in the hosts early development using quantitative fluorescence microscopy, and 3) to examine the symbiont role in environmental cue detection and the process of settlement by monitoring the expression of key metabolic enzymes in the symbionts.
