COMPARISON OF SELENIUM AND SULFUR VOLATILIZATION BY DIMETHYLSULFONIOPROPIONATE LYASE (DMSP) IN 2 MARINE-BACTERIA AND ESTUARINE SEDIMENTS

The volatile forms of selenium emitted from soils and plants have been identified by others as dimethylselenide and dimethyldiselenide. Dime thylselenoniopropionate, a possible precursor of dimethylselenide, is the selenium analogue of the common marine osmoprotectant, dimethylsul foniopropionate. Dimethylselenoniopropionate was organically synthesiz ed from dimethylselenide and acrylate and used in a comparative study with dimethylsulfoniopropionate as a growth substrate, an inducer and substrate for dimethylsulfoniopropionate lyase in two marine bacterial isolates, Alcaligenes sp. strain M3A and Pseudomonas doudoroffii, and in salt marsh sediments and estuarine creek water samples. In P. doud oroffii, the rate of dimethylselenoniopropionate transport into cells was about half that observed with dimethylsulfoniopropionate; Alcalige nes does not take up these molecules. The rate and extent of induction of dimethylsulfoniopropionate lyase in P. doudoroffii at low concentr ations of dimethylselenoniopropionate were similar to that of dimethyl sulfoniopropionate. In Alcaligenes the low constitutive level of dimet hylsulfoniopropionate lyase cleaved dimethylselenoniopropionate into d imethylselenide and acrylate, but induction of dimethylsulfoniopropion ate lyase by dimethylselenoniopropionate did not follow. Dimethylsulfo niopropionate lyases from both strains, when induced by dimethylsulfon iopropionate, utilized dimethylselenoniopropionate as a substrate with emission of dimethylselenide. Rates of partially purified dimethylsul foniopropionate lyase activity with dimethylselenoniopropionate were h alf those with dimethylsulfoniopropionate. Anoxic salt marsh sediments catalyzed dimethylsulfoniopropionate and dimethylselenoniopropionate degradation at equal rates. In sediments containing high organic matte r, both dimethylsulfide and dimethylselenide served as substrates for methanogenesis. These data support the hypothesis that organic seleniu m molecules can be volatilized by the same biochemical pathways as org anic sulfur molecules.