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 as part 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 in freshwater 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 the winter-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 to release DMS. Released fluxes of DMS from the Lake of Galilee are estimated to be in the range of 0.1 mmol/m 2 month during the late period of the Peridinium bloom season.

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The mechanism of formation of dimethyloligosulfides in Lake Kinneret was investigated by field and laboratory studies. The process was simulated under laboratory conditions using obligate aerobic and facultative bacteria that were isolated from Lake Kinneret and fed with different types of organo-sulfur nutrients. The lysis products of Peridinium gatunensea dinoflagellate that dominates the phytoplankton population in Lake Kinneret during the winter−spring seasonare the primary source of dimethyloligosulfides. Bacterial assimilation of the aged alga or algae lysis products yields inorganic oligosulfides, which are then methylated to form the dimethyloligosulfides. All the steps of this process are carried out under oxic conditions.

Dimethyloligosulfides were recently identified as a primary source of mild malodorous emissions from Lake Kinneret, Israel. The seasonal odor episodes coincide with a bloom of Peridinium gatunense algae. The possibility that the dimethyloligosulfides are formed by bacterial degradation of Peridinium gatunense lysis products, under oxygen rich conditions was investigated. Several bacterial strains were isolated from the lake. Addition of Peridinium cells to the isolated bacteria cultures yielded dimethyldisulfide and dimethyltrisulfide. One of the bacteria strains, identified as Acinetobacter lwoffii, an obligatory aerobe was singled out for detailed investigation. Addition of Peridinium cells or methionine to the Acinetobacter culture yielded, under aerobic conditions dimethyldisulfide and dimethyltrisulfide. Cystein feed yielded only inorganic oligosulfides, which were converted to dimethylsulfides by addition of d3-methyliodide.