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 large agricultural drainage evaporation basin in California. This mat was active in volatilizing Se from selenite at 20-10 000 μg/L Se, which 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 potentially important mechanism contributing to the nearly 100% loss of waterborne Se persistently observed at that basin. Se volatilization was via dimethylselenide, dimethyldiselenide, and dimethylselenenylsulfide, with evidence that the precursors were methylselenomethionine and methylselenocysteine but not dimethylselenonium propionate or trimethylselenonium ion. Selenite was also incorporated into proteins primarily in the form of selenomethionine at external Se concentrations of 5000 μg/L Se or higher, which may account for the slow growth of the cyanophyte mat at these concentrations such Se metabolite characterization in aquatic producers is important for understanding the role of Se biogeochemistry in ecotoxicity, which is vital for development of environmentally sound in situ Se bioremediation.