Methyl Selenol as Precursor in Selenite Reduction to Se/S Species by Methane-oxidizing Bacteria

A wide range of microorganisms have been shown to transform selenium-containing oxyanions to reduced forms of the element, particularly selenium-containing nanoparticles. Such reactions are promising for detoxification of environmental contamination and production of valuable selenium-containing products such as nanoparticles for application in biotechnology. It has previously been shown that aerobic methane-oxidising bacteria, including Methylococcus capsulatus (Bath), are able to perform methane-driven conversion of selenite (SeO3 2-) to selenium-containing nanoparticles and methylated selenium species. Here, the biotransformation of selenite by Mc. capsulatus (Bath) has been studied in detail via a range of imaging, chromatographic and spectroscopic techniques. The results indicate that the nanoparticles are produced extracellularly and have a composition distinct from nanoparticles previously observed from other organisms. The spectroscopic data from the methanotroph-derived nanoparticles are best accounted for by a bulk structure composed primarily of octameric rings in the form Se8-xSx with an outer coat of cell-derived biomacromolecules. Among a range of volatile methylated selenium and selenium-sulfur species detected, methyl selenol (CH3SeH) was found only when selenite was the starting material, although selenium nanoparticles (both biogenic and chemically produced) could be transformed into other methylated selenium species. This result is consistent with methyl selenol being an intermediate in methanotroph-mediated biotransformation of selenium to all the methylated and particulate products observed.ImportanceAerobic methane-oxidizing bacteria are ubiquitous in the environment. Two well characterised strains, Mc. capsulatus (Bath) and Methylosinus trichosporium OB3b, representing gamma- and alpha-proteobacterial methanotrophs, can convert selenite, an environmental pollutant, to volatile selenium compounds and selenium containing particulates. Both conversions can be harnessed for bioremediation of selenium pollution using biological or fossil methane as the feedstock and these organisms could be used to produce selenium-containing particles for food, and biotechnological applications. Using an extensive suite of techniques we identified precursors of selenium nanoparticle formation, and also that these nanoparticles are made up of eight membered mixed selenium and sulfur rings.