Sulphide tolerance of the marine nematode Oncholaimus campylocercoides-a result of internal sulphur formation?

Abstract

The free-living, marine nematode Oncholaimus campylocercoides occurs in high abundance (up to 600 ind. 10 cm-') at the fringe area of shallow-water hydrothermal vents off the Greek island of Milos in the Aegean Sea. It was found to have a sulphide tolerance (LTSO) of 4.5 d at 500 pM sulphide concentration and of 4 d at 1 mM sulphide. Light-and electron-rnicroscopical inspections showed that the non-symbiotic 0. campylocercoides, when exposed to sulpludic conditions, develops oily to viscous inclusions in the epidermis consisting of elemental sulphur in the form of &-rings and polysulphur chains. The longer the exposure to sulphidic conditions, the more sulphur was formed, which &sappeared after re-introduction of the nematodes in normoxic conditions for 12 h. Based on these results and on tolerance experiments with hydrogen sulphide, we suggest a model of sulphide metabolism in 0. campylocercoides which could relate to its occurrence in sulphidic, hydrothermal sediments.