Ecological physiology and biochemistry of sulfide acquisition by two hydrocarbon seep vestimentiferans, Lamellibrachia luymesi and Seepiophila jonesi

Two species of vestimentiferan tubeworm, Lamellibrachia luymesi and Seepiophila jonesi, co-occur in aggregations at northern Gulf of Mexico cold hydrocarbon seep sites. Like all vestimentiferans, L. luymesi and S. jonesi obtain nutrition from sulfide-oxidizing chemoautotrophic bacterial endosymbionts that must be supplied with sulfide, oxygen, and carbon dioxide. Results from previous studies that examined the environmental sulfide chemistry of northern Gulf of Mexico hydrocarbon seeps suggested that the ecological physiology of seep tubeworms was not analogous to that of the hydrothermal vent tubeworm, Riftia pachyptila, which obtains sulfide, oxygen, and carbon dioxide across the anterior plume portion of its body. The focus of this study was to better understand the physiological ecology of environmental sulfide acquisition of L. luymesi and S. jonesi. Whole animal respiration studies were conducted using split-vessel respiration chambers built specifically for this series of experiments. Methods for sulfide equilibrium dialysis experiments were determined and utilized to estimate the sulfide-binding characteristics of the intact fluids and component hemoglobins of L. luymesi and S. jonesi.; Split-vessel respiration experiments which exposed the root portions of L. luymesi to sulfide concentrations between 51 and 561 μM demonstrated that L. luymesi can utilize their roots as a respiratory surface to acquire sulfide at an average rate of 4.1 μmoles*g −1*h−1. Net dissolved inorganic carbon uptake across the plume of the tubeworms was shown to occur in response to exposure of the posterior, root portion of the worms to sulfide, demonstrating that sulfide acquisition by roots of the seep vestimentiferan L. luymesi can be sufficient to fuel net autotrophic total dissolved inorganic carbon uptake.; Results from sulfide-binding experiments show that the 3,500 kDa Hb from the fluids of S. jonesi has a high affinity for sulfide ( C₅₀ value of 8.8μM) while the 3,500 kDa Hb from the fluids of L. luymesi has only a moderate affinity for sulfide (C₅₀ value of 96μM). S. jonesi has elevated fluid heme concentrations that may facilitate the survival of individuals in environments where they are exposed to low concentrations of oxygen and/or short periods without any oxygen. The high affinity of the predominant hemoglobin in the vascular fluid of S. jonesi for sulfide suggests that large S. jonesi may be capable of acquiring sulfide with the anterior plume portion of its body from low concentration pools found just above the sediment-water interface.; Together these data have fundamentally changed our model for the ecological physiology of seep vestimentiferans. Although closely related to hydrothermal vent tubeworms, L. luymesi and S. jonesi do not acquire metabolites from the environment in the same way as R. pachyptila. We are now beginning to understand how sulfide, carbon dioxide, and oxygen can be acquired by L. luymesi and S. jonesi. (Abstract shortened by UMI.)...