Accumulation of Amorphous Cr(III)–Te(IV) Nanoparticles on the Surface of <i>Shewanella oneidensis</i> MR‑1 through Reduction of Cr(VI)

Industrial effluents constitute a major source of metal pollution of aquatic bodies. Moreover, due to their environmental persistence, toxic metal pollution is of special concern. Microbial reduction is considered a promising strategy for toxic metal removal among the several methods available for metal remediation. Here, we describe the coremediation of toxic Cr­(VI) and Te­(IV) by the dissimilatory metal reducing bacterium-<i>Shewanella oneidensis</i> MR-1. In the presence of both Cr­(VI) and Te­(IV), <i>S. oneidensis</i> MR-1 reduced Cr­(VI) to the less toxic Cr­(III) form, but not Te­(IV) to Te(0). The reduced Cr­(III) ions complexed rapidly with Te­(IV) ions and were precipitated from the cell cultures. Electron microscopic analyses revealed that the Cr–Te complexed nanoparticles localized on the bacterial outer membranes. K-edge X-ray absorption spectrometric analyses demonstrated that Cr­(III) produced by <i>S. oneidensis</i> MR-1was rapidly complexed with Te­(IV) ions, followed by formation of amorphous Cr­(III)–Te­(IV) nanoparticles on the cell surface. Our results could be applied for the simultaneous sequestration and detoxification of both Cr­(VI) and Te­(IV) as well as for the preparation of nanomaterials through environmental friendly processes

Methanogenesis Facilitated by Geobiochemical Iron Cycle in a Novel Syntrophic Methanogenic Microbial Community

Production and emission of methane have been increasing concerns due to its significant effect on global climate change and the carbon cycle. Here we report facilitated methane production from acetate by a novel community of methanogens and acetate oxidizing bacteria in the presence of poorly crystalline akaganeite slurry. Comparative analyses showed that methanogenesis was significantly enhanced by added akaganeite and acetate was mostly stoichiometrically converted to methane. Electrons produced from anaerobic acetate oxidation are transferred to akaganeite nanorods that likely prompt the transformation into goethite nanofibers through a series of biogeochemical processes of soluble Fe­(II) readsorption and Fe­(III) reprecipitation. The methanogenic archaea likely harness the biotransformation of akaganeite to goethite by the Fe­(III)–Fe­(II) cycle to facilitate production of methane. These results provide new insights into biogeochemistry of iron minerals and methanogenesis in the environment, as well as the development of sustainable methods for microbial methane production