DIMETHYLSULFONIOPROPIONATE IN ANOXIC INTERTIDAL SEDIMENTS - A PRECURSOR OF METHANOGENESIS VIA DIMETHYL SULFIDE, METHANETHIOL, AND METHIOLPROPIONATE

The most important volatile sulfur compound in the marine environment is dimethyl sulfide (DMS), which mainly originates from the algal osmo lyte dimethylsulfoniopropionate (DMSP). Conversion of DMSP in anoxic m arine sediments involves a cleavage to acrylate and DMS, which can fur ther be converted by methanogenic Archaea and possibly by sulfate-redu cing bacteria, or a demethylation to 3-methiolpropionate (MMPA); MMPA can be demethylated to 3-mercaptopropionate or demethiolated to methan ethiol and presumably acrylate. Little is known about the types of ana erobic microorganisms that are involved in the demethylation pathway. We found that the marine Desulfobacterium strain PM4 converts DMSP to MMPA and that three marine Methanosarcina strains demethylate MMPA to S-mercaptopropionate and methane. Methanogenic conversion of MMPA in a noxic sediment slurries was only found when antibiotics that inhibit B acteria but not Archaea were added. Under non-inhibited conditions MMP A was rapidly converted to methanethiol and subsequently to methane. T he numbers of MMPA-metabolizing methanogens were significantly lower t han those of DMS-, trimethylamine-, or methanol-metabolizing methanoge ns. It is concluded that in anoxic intertidal sediments DMSP is not on ly a source of DMS with its well-known counteractive effect on global warming, but also of the potent greenhouse gas methane.