WOHLGEMUTH, S.E.*; JULIAN, D.; ARP, A.J.: Induction of sulfide-oxidizing bodies in the epidermis of the annelid worm Branchioasychis americanus after sulfide exposure

A characteristic feature of some sulfide-adapted marine invertebrates is the presence of electron-dense inclusion bodies in the epidermis, such as have been reported in the echiuran worm Urechis caupo and the clam Solemya reidi. These inclusion bodies have been proposed to oxidize sulfide and have therefore been called sulfide-oxidizing bodies (SOBs). Thus far, nothing has been known about the origin or fate of SOBs or the mechanism by which they are formed. In this study, we tested whether SOBs could be induced in the epidermis of a sulfide-adapted animal. Branchioasychis americanus (annelida) were collected from sulfidic mudflats on the Florida gulf coast. After two to four weeks of incubation in sulfide-free seawater, the worms were exposed to hydrogen sulfide for 24 h. After 0, 8, and 24 h recovery, body wall samples from the worms were fixed and examined using transmission electron microscopy. Samples were also examined from control B. americanus, which were not exposed to sulfide but were otherwise identical. We found that the sulfide-exposed animals had 3 times more electron-dense inclusion bodies in the epidermal layer of the body wall tissue than the control animals (p < 0.001). These inclusion bodies were membrane-bound and were generally similar in appearance to SOBs in U. caupo and S. reidi. This study demonstrates for the first time that SOBs are inducible, that they are formed rapidly (within 24 hours), and that their formation is related to sulfide exposure.