Combined bioreduction and volatilization of SeVI by Stenotrophomonas bentonitica: Formation of trigonal selenium nanorods and methylated species

Nowadays, metal pollution due to the huge release of toxic elements to the environment has become one of the world's biggest problems. Bioremediation is a promising tool for reducing the mobility and toxicity of these contaminants (e.g. selenium), being an efficient, environmentally friendly, and inexpensive strategy. The present study describes the capacity of Stenotrophomonas bentonitica to biotransform SeVI through enzymatic reduction and volatilization processes. HAADF-STEM analysis showed the bacterium to effectively reduce SeVI (200 mM) into intra- and extracellular crystalline Se0 nanorods, made mainly of two different Se allotropes: monoclinic (m-Se) and trigonal (t-Se). XAS analysis appears to indicate a Se crystallization process based on the biotransformation of amorphous Se0 into stable t-Se nanorods. In addition, results from headspace analysis by gas chromatography-mass spectometry (GC–MS) revealed the formation of methylated volatile Se species such as DMSe (dimethyl selenide), DMDSe (dimethyl diselenide), and DMSeS (dimethyl selenenyl sulphide). The biotransformation pathways and tolerance are remarkably different from those reported with this bacterium in the presence of SeIV. The formation of crystalline Se0 nanorods could have positive environmental implications (e.g. bioremediation) through the production of Se of lower toxicity and higher settleability with potential industrial applications. [Display omitted] •S. bentonitica is first described for reducing hazardous Se(VI) to Se(0) nanorods.•The Se products are present in two different allotropes, monoclinic and trigonal.•The bacterium S. bentonitica showed novel features in reducing Se(VI).•S. bentonitica is a potential candidate for bioremediation of Se(VI).•This work provides a promising green synthesis of Se nanorods of industrial interest.