|
Dr. Craig Cary's Abstracts
Habitat characterization and nutritional
strategies of the endosymbiont-bearing bivalve, Lucinoma aequizonata. Abstract
A population of the lucinid bivalve Lucinoma aequizonata, with sulfur-oxidizing endosymbiotic bacteria in the gills, is restricted to a narrow depth range (500ñ10 m) on the slope of the Santa Barbara Basin, California, USA. In this zone, the seawater just above the substratum is sub-oxic ([02] <20 M). The organically rich sediments in which these clams live are well mixed by bioturbation, which appears to maintain a redox condition limiting the extensive accumulation of hydrogen sulfide. However, thiol levels in the blood of the clams indicate an exposure to significant amounts of sulfide and/or thiosulfate apparently from randomly dispersed short-lived pockets of sulfidic mud that can be reached by the clam's burrowing vermiform foot. When the bivalves are incubated in the presence of hydrogen sulfide, thiosulfate is concentrated in the blood and apparently utilized by the bacteria for metabolic energy and the production of intracellular elemental sulfur. The utilization of thiosulfate under near anaerobic conditions and the accumulation of intracellular elemental sulfur by the endosymbiotic bacteria coupled with the high availability of environmental nitrate and low molecular oxygen suggests a metabolic strategy analogous to the free-living sulfur oxidizer Thiobacillus denitrificans. The ë13C values of the purified endosymbiont bacteria ( 34.0 ñ 0.8%) were significantly lighter than those of the host tissue ( 29.0 ñ 0.7%) suggesting that in addition to the nutrition provided by the bacteria, over 25% of the host carbon may be attributed to exogenous dissolved carbon which is high concentrations in its natural habitat. |
