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-2) 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 (LT50) of 4.5 d at 500 μM sulphide concentration and of 4 d at 1 mM sulphide. Light- and electron-microscopical inspections showed that the non-symbiotic O. campylocercoides, when exposed to sulphidic conditions, develops oily to viscous inclusions in the epidermis consisting of elemental sulphur in the form of S8-rings and polysulphur chains. The longer the exposure to sulphidic conditions, the more sulphur was formed, which disappeared 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 O. campylocercoides which could relate to its occurrence in sulphidic, hydrothermal sediments.