BIOTRANSFORMATIONS OF SELENIUM OXYANION BY FILAMENTOUS CYANOPHYTE-DOMINATED MAT CULTURED FROM AGRICULTURAL DRAINAGE WATERS

A filamentous cyanophyte-dominated mat was cultured from waters of a l arge agricultural drainage evaporation basin in California. This mat w as active in volatilizing Se from selenite at 20-10000 mu g/L Se, whic h accounted for >60% of the Se loss from the medium. Up to 75% of the medium Se was depleted over a 50-day period. This demonstrates a poten tially important mechanism contributing to the nearly 100% loss of wat erborne Se persistently observed at that basin. Se volatilization was via dimethylselenide, dimethyldiselenide, and dimethylselenenylsulfide , with evidence that the precursors were methylselenomethionine and me thylselenocysteine but not dimethylselenonium propionate or trimethyls elenonium ion. Selenite was also incorporated into proteins primarily in the form of selenomethionine at external Se concentrations of 5000 mu g/L Se or higher, which may account for the slow growth of the cyan ophyte mat at these concentrations. Such Se metabolite characterizatio n in aquatic producers is important for understanding the role of Se b iogeochemistry in ecotoxicity, which is vital for development of envir onmentally sound in situ Se bioremediation.