ENVIRONMENTAL IMPACT OF FUNGI-MEDIATED REDOX TRANSFORMATIONS OF SELENIUM

Although microfungi are prevalent and active in soil and water ecosystems, little is understood about their role in metal redox transformations and ultimate impact on environmental health. Microbiologically mediated redox transformations of selenium (Se), a metal of increasingly significant environmental concern, greatly influence its solubility, bioavailability, and toxicity. Ongoing research has established that several common soil fungi aerobically reduce soluble, bioavailable Se(IV,VI) anions to insoluble Se(0). In this research, we assess the contribution of fungal pathways for aerobic Se transformations.

Six common soil Ascomycete microfungi were previously isolated from a metalliferous environment and studied with respect to their ability to oxidize Mn(II) to sparingly soluble Mn(III,IV)(hydr)oxide minerals. For this study, batch cultures of these fungal isolates were grown in the presence of Se(IV) or Se(VI) to determine the effects of Se on fungal growth rates, metal tolerance, and Se-redox transformations. All six isolates were able to remove soluble Se from solution in aerobic conditions, although removal of Se from solution was substantially lower at higher Se concentrations likely due to toxicity effects. The magnitude of Se removal, as well as the maximum tolerated concentration, differed both based on fungal species present and whether the isolates were grown in media containing Se(IV) or Se(VI). Specifically in all six species, greater Se(IV) was removed from solution and a red, nanoparticulate Se(0) mineral was observed in many of the cultures indicating partial or complete reduction of the metal. Results from this study are key for understanding Se-transforming reactions in soils, and the role that fungi play in influencing Se bioavailability and mobility within and out of contaminated ecosystems.