Dimethyl sulphoxide (DMSO) and dimethyl sulphide (DMS) as inhibitors of methane oxidation in forest soil

Dimethyl sulphoxide (DMSO) at 14 mM inhibits CH4 oxidation in forest soil, but the inhibition mechanism is unknown. When soil slurries are incubated in gas tight flasks, there is a lag of about 45 h before DMSO inhibits CH4 oxidation. We tried to determine if some metabolic compound derived from DMSO, as a result of microbial activity, is responsible for the inhibition. Dimethyl sulphide (DMS) accumulated in the sealed flasks up to 5–83 μl l−1 in the headspace during a 2-week period. DMS at 1 μl l−1 in the headspace (0.64 μM in soil–water slurry) had a negligible effect on CH4 oxidation but 50 μl l−1 DMS (32 μM) inhibited CH4 oxidation completely. However, the inhibition by DMSO was already evident after 45 h, when DMS concentrations were generally non-inhibiting (0.1–0.7 μl l−1). DMSO was also shown to inhibit CH4 oxidation when the DMS produced was continuously removed. Results suggest that the production of DMS from DMSO makes a minor contribution to the inhibition of CH4 oxidation by DMSO with incubation times relevant in CH4 oxidation studies.