MICROBIAL FORMATION OF DIMETHYL SULFIDE IN ANOXIC SPHAGNUM PEAT

Peat bogs dominated by Sphagnum spp. have relatively high areal rates of dimethyl sulfide (DMS) emission to the atmosphere. DMS was produced in anoxic slurries of Sphagnum peat with a linear time course and wit h an average rate of 40.4 (range, 22.0 to 68.6) nmol per liter of slur ry day(-1) observed in nine batches of slurry. Methanethiol (MeSH) was produced at roughly similar rates over the typical 4- to 8-day incuba tions. DMS and MeSH production in these acidic (pH 4.2 to 4.6) peats w ere biological, as they were stopped completely by autoclaving and inh ibited strongly by addition of antibiotics and 500 mu M chloroform. En dogenous DMS production may be due to the degradation of S-methyl-meth ionine, dimethyl sulfoxide, or methoxyaromatic compounds (e.g., syring ic acid), each of which stimulated DMS formation when added at 5 to 10 mu M concentrations. However, on the basis of the high rates of thiol (MeSH and ethanethiol) methylation activity that we observed and the availability of endogenous MeSH, we suggest that methylation of MeSH i s the major pathway leading to DMS formation in anaerobic peat. Solid- phase adsorption of MeSH plays a key role in its availability for biom ethylation reactions. Additions of acetate (1.5 mM) or compounds which could cause acetate to accumulate (e.g., glucose, alanine, and 2-brom oethanesulfonate) suppressed DMS formation. It is likely that acetogen ic bacteria are involved in DMS formation, but our data are insufficie nt to allow firm conclusions about the metabolic pathways or organisms involved. Our observations are the first which point to the methylati on of MeSH as the major mechanism for endogenous DMS production in any environment. The rates of net DMS production observed are sufficient to explain the relatively high fluxes of DMS emitted to the atmosphere from Sphagnum sp.-dominated wetlands.