DECOMPOSITION OF DISSOLVED DMSP AND DMS IN ESTUARINE WATERS - DEPENDENCE ON TEMPERATURE AND SUBSTRATE CONCENTRATION

Dimethylsulfide (DMS) is an important trace gas which is emitted from seawater to the atmosphere. DMS is believed to be derived primarily from the plant osmolyte 3-(dimethylsulfonium)propionate (DMSP). This study examined the decomposition of dissolved DMSP (DMSP(diss)), the production of DMS from DMSP(diss), and the consumption of DMS in estuarine waters near Sapelo Island, Georgia, USA. Rate of DMSP(diss) disappearance from seawater was directly proportional to the concentration of DMSP(diss), over the range of concentrations tested (20 to 100 nM), and was a function of temperature; rates were very low at 4-degrees-C and increased progressively at 16, 23 and 30-degrees-C. At 49-degrees-C the rate of DMSP(diss) metabolism was substantially lower. The production of DMS from DMSP(diss) displayed similar concentration and temperature dependence. However, a mass balance of total DMSP during dark incubations indicated that < 30% of the DMSP consumed during the experiments was converted to DMS, even when chloroform (500-mu-M) was included to prevent DMS consumption. Chloroform did not affect DMSP decomposition or DMS production from this compound. Thus, we conclude that DMS is not the major sulfur product of DMSP metabolism in estuarine waters. An alternative route for DMSP metabolism, possibly involving demethylation, is suggested. Rate of DMS consumption was directly dependent on DMS concentration and incubation temperature. DMS metabolism was strongly inhibited by chloroform (500-mu-M) and azide (0.25%). Results suggest that DMS production and consumption may be closely coupled in natural seawater since both these processes displayed similar concentration and temperature dependence. The characteristics (kinetic parameters) of the enzyme systems involved in DMS production and consumption are likely to play a major role in controlling the concentration of DMS in seawater.