Hemoglobin in the symbiont-harboring gill of the marine gastropod Alviniconcha hessleri.

Hydrogen sulfide of geochemical origin, mixing at oceanic hydrothermal vents with oxygen from oceanic seawater, supports dense populations of chemoautrophic, sulfur-oxidizing bacteria. Those animals, the vestimentiferan worm Riftia pachyptila, certain bivalve molluscs, and the recently discovered Pacific gastropod Alviniconcha hessleri, that interiorize the bacteria as intracellular symbionts dominate the vent fauna (1, 2). The immense size of these animals, the large standing crop represented in their dense communities, and the rapid growth of individuals all attest to the effective use of an abundant food base. Dense concentrations of the mesogastropod Alviniconcha hessleri (2, 3) were recently discovered at deep-sea hydrothermal vents at the spreading center in the Mariana Back-Arc Basin of the Western Pacific. These animals house chemoautrophic, sulfide-oxidizing bacteria within specialized cells (bacteriocytes) of their modified gills (2). They are the only reported example of a symbiotic association between a gastropod mollusc and intracellular chemoautotrophic bacteria. We now show that the modified gill of Alviniconcha contains hemoglobin at a concentration of about 65 mumol/kg wet weight gill. This value falls within the range, 20-250 mumol hemoglobin per kilogram, encountered in the modified symbiont-harboring gills of many of the sulfide-dependent clams examined but is short of the very high concentrations, 550 and 1200 mumol/kg, found in Myrtea spinifera and Lucina pectinata respectively (4). Accordingly, bacteriocyte hemoglobin is a feature common to both gastropod and bivalve symbioses.