Exudation of low molecular weight compounds (thiobismethane, methyl isocyanide, and methyl isothiocyanate) as a possible chemical defense mechanism in the marine sponge Ircinia felix

The volatile constituents of the marine sponge Ireinia felix were obtained by dynamic headspace extraction and analyzed by HRGC, HRGC-R IS and HRGC-Od or at sniffling port. Fifty-nine volatiles were identified for the first ti me in the odor of this sponge. Hydrocarbons (32.9%), alcohols (17.8%) and c arbonyl compounds (16.0%) predominated in the sponge volatile profile, foll owed by esters (11.6%), halogen compounds (8.6%). ethers (7.7%), nitrogen a nd-or sulfur compounds (4.6%)) and carboxylic acids (0.8%). Among the ident ified volatiles, thiobismethane (commonly known as dimethylsulfide), methyl isocyanide and methyl isothiocyanate were found to be responsible for the nauseating and toxic smell emitted by the sponge and for the antimicrobial activity detected in the volatile extract. Exudation experiments in aquariu m and in situ conditions revealed that thiobismethane. methyl isocyanide an d methyl isothiocyanate are continuously released by the sponge. Upon injur y, the concentration of these volatiles increased strongly. Hence. these su bstances Form a chemical protective barrier which may help these sponges av oid fouling. compete for space, prevent infection in the short term, and!:o r signal generalist predators regarding the existence of other toxic substa nces in the internal tissues. (C) 2001 Elsevier Science Ltd. All rights res erved.