Selenium (Se) redox chemistry is a determining factor for its environmental toxicity and mobility. Currently, millions of people are impacted by Se deficiency or toxicity, and in geologic history, several mass extinctions have been linked to extreme Se deficiency. Importantly, microbial activity and interactions with other biogeochemically active elements can drastically alter Se oxidation state and form, impacting its bioavailability. Here, we use wet geochemistry, spectroscopy, and electron microscopy to identify a cryptic, or hidden, Se cycle involving the reoxidation of biogenic volatile Se compounds in the presence of biogenic manganese [Mn(III, IV)] oxides and oxyhydroxides (hereafter referred to as "Mn oxides"). Using two common environmental Ascomycete fungi, Paraconiothyrium sporulosum and Stagonospora sp., we observed that aerobic Se(IV and VI) bioreduction to Se(0) and Se(-II) occurs simultaneously alongside the opposite redox biomineralization process of mycogenic Mn(II) oxidation to Mn oxides. Selenium bioreduction produced stable Se(0) nanoparticles and organoselenium compounds. However, mycogenic Mn oxides rapidly oxidized volatile Se products, recycling these compounds back to soluble forms. Given their abundance in natural systems, biogenic Mn oxides likely play an important role mediating Se biogeochemistry. Elucidating this cryptic Se cycle is essential for understanding and predicting Se behavior in diverse environmental systems.
Bibliographical noteFunding Information:
Research was supported by an NSF EAR Postdoctoral Fellowship (C.E.R., Grant #: 1452666) and by MnDRIVE Environment (C.M.S.). ICP-OES was performed in the UMN Department of Earth Sciences analytical geochemistry laboratory. This research used resources of the Advanced Photon Source, a U.S. Department of Energy Office of Science User Facility operated by Argonne National Laboratory under contract DE-AC02-06CH11357. We thank beamline scientists Ben Reinhart and Sungsik Lee for assistance with XAS data collection and Christine Hitomi and Josh Torgeson for experimental assistance. TEM was carried out in the UMN Characterization Facility, a member of the NSF-funded Materials Research Facilities ( www.mrfn.org ) via the MRSEC program. We thank Fang Zhou for help with TEM sample preparation and Jason Meyers for help with TEM analysis. XRD was performed at the Smithsonian Institution NMNH Department of Mineral Sciences. We also thank Jingru Chen and Michael Winikoff (UMN, BTI) for assistance with the conceptual diagram.
Copyright © 2020 American Chemical Society.
PubMed: MeSH publication types
- Journal Article
- Research Support, Non-U.S. Gov't
- Research Support, U.S. Gov't, Non-P.H.S.