Dimethyl sulfide, the most important form of sulfur gas, is formed by bacterial degradation of dimethylsulfoniopropionate (DMSP) in the Lake of Galilee. DMSP is believed to be a methionine metabolite produced by marine algae and higher plants aspart of their osmoregulatory systems. Until now, this process was found exclusively in saline water and therefore was regarded as insignificant for the formation of DMS in freshwaters. It is hereby demonstrated that the process can be dominant infreshwater systems as well, and its product can even affect the odor quality of some drinking and recreational water systems. Peridinium gatunense, a freshwater dinoflagellate which dominates the phytoplankton population in the lake during thewinter-spring season, stores a considerable amount (up to 5.5 pg/cell) of DMSP. P. gatunense growth curves reveal an increased storage of DMSP toward the stationary and declining growth phases. The DMSP undergoes bacterial and chemical degradation torelease OMS. Released fluxes of DMS from the Lake of Galilee are estimated to be in the range of 0.1 mmol/m{sup}2 month during the late period of the Peridinium bloom season.
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