SULFIDE TOLERANCE AND DETOXIFICATION IN ARENICOLA-MARINA AND SIPUNCULUS-NUDUS

The lugworm Arenicola marina and the peanut worm Sipunculus nudus both inhabit intertidal flats. Sulfide concentrations in the pore water of the sediment can be as high as 340 mu M in the habitat of A. marina. Sulfide levels in the burrow water and in the coelomic fluid increase during low tide. In contrast, S, nudus is only rarely exposed to sulfi de. Neither A. marina nor S, nudus is able to exclude sulfide complete ly from its body. However, both worms accumulate only 15 to 40% respec tively of the external sulfide concentration during hypoxic 1 mM sulfi de incubations. During normoxia, sulfide accumulation is more than ten -fold lower than under hypoxic conditions in both species. When oxygen is available, sulfide is oxidized to thiosulfate. The oxidation rate is about 5 times higher in A. marina than in S. nudus. A major compone nt of sulfide oxidation is due to the mitochondria of both species. Mi tochondrial sulfide oxidation in the tissues of A. marina is insensiti ve to low cyanide and to high sulfide concentrations, but can be inhib ited by salicylhydroxamic acid. The existence of an alternative termin al oxidase is suggested. When the sulfide level in the body of A. mari na and S. nudus increases above a toxic level, both species survive by switching to an anaerobic metabolism.