Sulfide binding in the body fluids of hydrothermal vent alvinellid polychaetes

Dissolved H₂S is a major environmental factor in hydrothermal vent ecosystems. In a study of adaptations to sulfide by alvinellid polychaetes, the sulfide-binding capacity of body fluids was examined in Paralvinella palmiformis from northeast Pacific ridges and Alvinella species from the East Pacific Rise. Sulfide concentrations in vascular blood and coelomic fluid of freshly collected animals were notably variable. Separation of P. palmiformis bodyfluid components revealed that most sulfide (ca. 77%) was accumulated in the dissolved fraction. In P. palmiformis, both vascular blood and coelomic fluid could reversibly bind sulfide in vitro with a low affinity, saturating only at high dialysate concentrations (ca. 2 mmol L^-1). No sulfide-binding activity was observed in the vascular blood from Alvinella species. A dissolved protein component of greater than 90 kDa appears to be involved in sulfide binding in Paralvinella, probably a vascular extracellular high-molecular-weight hemoglobin. Some sulfide may also adsorb onto a 15.35-kDa intracellular hemoglobin present in the coelomic erythrocyte fraction. In the absence of epibiotic bacteria, Paralvinella body fluids may function as a sulfide buffer to protect tissues from deleterious effects of sulfide exposure.