Sulfide Tolerance and Detoxification inArenicola marinaandSipunculus nudus

Abstract

SYNOPSIS. 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 μM 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 sulfide. Neither A. marina nor S. nudus is able to exclude sulfide completely from its body. However, both worms accumulate only 15 to 40% respectively of the external sulfide concentration during hypoxic 1 mM sulfide 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 component of sulfide oxidation is due to the mitochondria of both species. Mitochondrial sulfide oxidation in the tissues of A. marina is insensitive to low cyanide and to high sulfide concentrations, but can be inhibited by salicylhydroxamic acid. The existence of an alternative terminal oxidase is suggested. When the sulfide level in the body of A. marina and S. nudus increases above a toxic level, both species survive by switching to an anaerobic metabolism.