Selenium biotransformations by a euryhaline microalga isolated from a saline evaporation pond

Selenium ecotoxicology is one of the best known examples of environmental impact resulting from toxic element biotransformations and food chain transfers. Despite this, it is becoming recognized that Se biotransformations by microbes and plants may also be a key to in situ bioremediation of Se contamination in large-scale cases such as agricultural drainage systems. We have isolated an euryhaline alga (Chlorella sp.)from Se- laden drainage pond waters and utilized GC-MS and multi-nuclear NMR to characterize its aerobic biotransformation activity for Se oxyanions. We found that this alga was active in volatilization of alkylselenides, production of putative selenonium precursor(s) of alkyl-selenides, and precipitation of Se, while exhibiting very low accumulation of the toxic selenomethionine in free form. Thus, such euryhaline microalgae are potentially important for in situ Se bioremediation and Se biogeochemical cycling in contaminated saline habitats.