Cytoplasmic hemoglobins characteristic of nearly all bivalves and gastropod molluscs in which chemoautotrophic bacteria are present as internal symbionts appear vital to the symbiosis. Three such hemoglobins, from gills of the clam Lucina, have been isolated and their interactions with either sulfide or oxygen determined. The role(s) of these hemoglobins in the symbiotic association will now be examined using broken-cell systems containing symbiotic bacteria, kpurified gill hemoglobins, sulfide, and oxygen. The molecular mechanisms of cytoplasmic hemoglobin-mediated oxygen delivery and sulfide delivery to the bacterial symbionts will be studied; the effects of reduction of either heme or the ligand on ligand dissociation will be examined. Our understanding of the means whereby the bacteria utilize carbon dioxide using energy gained from sulfide oxidation, thus supporting life of this clam and other similar macrobes should be enhanced by these studies. The particular roles and mechanisms whereby hemoglobins, present in the cytoplasm of certain marine invertebrates in which an unusual symbiosis involving internalized chemoautotrophic bacteria exists, will be studied in terms of the ability of the invertebrate's hemoglobins to transport oxygen and sulfide to the bacteria. This inter-dependence of micro- and the macro-organism is an increasingly recognized one; an understanding of the means whereby sulfide, toxic to the invertebrate, reaches the symbiont and is protected from oxygen should be enlarged by this study. //
