CONCOMITANT EFFECTS OF SULFIDE AND HYPOXIA ON THE AEROBIC METABOLISM OF THE MARINE OLIGOCHAETE TUBIFICOIDES BENEDII

Sulfide is toxic for most aerobic organisms and inhibits the key enzym e of aerobic respiration, cytochrome c oxidase, at low mu M concentrat ions. Tubificoides benedii is a ubiquitous marine oligochaete that reg ularly occurs in polluted, poorly oxidized coastal muds with high sulf ide concentrations. The questions posed in this study were: Can T. ben edii maintain aerobic pathways despite the occurrence in its habitat o f sulfide concentrations that are toxic for many marine invertebrates? What influence does the ambient oxygen concentration have on the sulf ide effects? To answer these questions animals were incubated under fl ow-through conditions in various sulfide and oxygen concentrations. As an indicator of an anaerobic metabolism succinate was measured, a met abolite which accumulates in high concentrations in T. benedii under h ypoxic conditions. The results show that under normoxic conditions, T. benedii can maintain a completely aerobic metabolism at sulfide conce ntrations up to 175 mu M. At 300 mu M sulfide, anaerobic pathways are utilized to only a small extent and even at sulfide concentrations as high as 450 mu M and 600 mu M a partially aerobic metabolism is sustai ned. However, if ambient oxygen concentrations are decreased, much low er sulfide concentrations cause the animal to utilize anaerobic pathwa ys. At oxygen concentrations as low as 20 mu M (= 1.5 kPa O-2 or 7% ai r saturation), where the worms can maintain a fully aerobic metabolism in the absence of sulfide, minimal concentrations of sulfide (40 mu M ) are sufficient to give rise to an anaerobic metabolism. (C) 1994 Wil ey-Liss, Inc.