ULTRASTRUCTURE AND ANAEROBIC METABOLISM OF MITOCHONDRIA IN THE MARINEOLIGOCHAETE TUBIFICOIDES BENEDII - EFFECTS OF HYPOXIA AND SULFIDE

It has often been suggested that ultrastructural properties of mitocho ndria are correlated with oxygen and sulfide levels from the environme nt, although careful analyses of this question are rare. In this study the ultrastructure and distribution of mitochondria in Tubificoides b enedii, a marine oligochaete from sulfide-rich sediments, were investi gated after a series of oxic, hypoxic and hypoxic-sulfidic (200 mu M H 2S) incubations up to 24 h. Succinate, one of the key endproducts of a n anaerobic metabolism, was used as an indicator of mitochondrial anae robiosis. Consistent differences in mitochondrial ultrastructure were not observed in any of the incubations, even after 24 h. Stereological parameters of mitochondria (volume density, surface density of the ou ter mitochondrial membrane, and specific surface) in epidermal and int estinal tissues of T. benedii were not affected by hypoxia or sulfide either. On the other hand, succinate concentrations increased signific antly within 24 h under hypoxic and hypoxic-sulfidic conditions. Thus, experimental hypoxia and sulfide clearly caused mitochondrial anaerob iosis without affecting ultrastructure or distribution of mitochondria in T. benedii. Distinct differences in ultrastructural and stereologi cal parameters were common between different tissues and between indiv iduals, showing that different forms of mitochondria can occur within one species. Our results imply that a mitochondrial ultrastructure spe cific to thiobiotic animals does not appear to exist.