Selenium is a naturally occurring trace element in the earth's crust, a micronutrient for humans and wildlife but toxic at high concentrations. Microbial biotechnologies have emerged as eco-friendly, sustainable research fields for the dismissal or recovery of Se to impede environmental issues. Microorganisms and their metabolites, such as extracellular polymeric substances (EPS), play an essential role in the redox transformation and remediation of metalloids. EPS are a complex suite of macromolecules in biofilms at the "soil-microbe" interface and has potential application prospects in environmental remediation technologies. Accumulative evidence has shown that EPS are related to the extracellular accumulation and redox transformation of metalloids in microbial cells. However, how EPS affects Se oxyanions redox cycling in aquatic systems and what are the underlying mechanisms, especially electron transfer mechanisms and which components of EPS are involved in Se redox transformation are not very clear. Even though our recent research on selenite reduction by Bacillus safensis JG-B5T showed that the reduction of selenite to selenium nanoparticles (BioSeNPs) predominantly occurred through the extracellular membrane-associated proteins, like succinate dehydrogenase, there is still knowledge gap, especially concerning electron transfer mechanisms between EPS-Se oxyanions to form bioSeNPs and which redox-active components of EPS are involved in the redox cycling of Se oxyanions. To what extent do this pure culture strain-derived EPS-Se oxyanions reduction mechanisms apply to an up-flow anaerobic sludge blanket (UASB) reactor for practical use of EPS for bioSeNPs recovery or Se remediation remains unknown.
To answers these questions, we plan to set up in situ and in vitro microcosms combined with electrochemical and spectroscopic techniques to examine: 1) the key agents and structural components of EPS involved in the reduction of Se(IV/VI), 2) the electron transfer mechanisms between EPS and Se oxyanions for the reduction of Se(IV/VI); 3) the significance of the Se reduction to the environmental fate and recovery of bioSeNPs in UASB reactor. The results from this project will be vital to clarifying the role of microbial EPS and their components in the BioSeNPs cycle and developing biotechnologies to remediate and recover environmental Se.
