Structural Similarities between Biogenic Uraninites Produced by Phylogenetically and Metabolically Diverse Bacteria

Abstract

While the product of microbial uranium reduction is often reported to be "UO 2 ", a comprehensive characterization including stoichiometry and unit cell determination is available for only one Shewanella species. Here, we compare the products of batch uranyl reduction by a collection of dissimilatory metal-and sulfate-reducing bacteria of the genera Shewanella, Geobacter, Anaeromyxobacter, and Desulfovibrio under similar laboratory conditions. Our results demonstrate that U(VI) bioreduction by this assortment of commonly studied, environmentally relevant bacteria leads to the precipitation of uraninite with an approximate composition of UO 2.0 , regardless of phylogenetic or metabolic diversity. Coupled analyses, including electron microscopy, X-ray absorption spectroscopy, and powder diffraction, confirm that structurally and chemically analogous uraninite solids are produced. These biogenic uraninites have particle diameters of about 2-3 nm and lattice constants consistent with UO 2.0 and exhibit a high degree of intermediate-range order. Results indicate that phylogenetic and metabolic variability within delta-and gamma-proteobacteria has little effect on biouraninite structure or crystal size under the investigated conditions.

Products of abiotic U(VI) reduction by biogenic magnetite and vivianite

“…the number of U atoms bound at the surface of the particle becomes comparable to the number of U atoms within the interior of the particle, resulting in a decrease in the average U-U CN (4.1-6.1), which is consistent with EXAFS in the present study. This under-coordination is consistent with the nanoparticulate size and consequential high proportion of surface-exposed atoms (O'Loughlin et al, 2003;Schofield et al, 2008;Veeramani et al;Sharp et al, 2009). The same EXAFS results were observed for both unpasteurized and pasteurized magnetite samples, confirming that an abiotic process leads to uraninite formation.…”

“…These experiments were performed in a simple chemical matrix according to the method described by Sharp et al (2009).…”

Extracellular reduction of uranium via Geobacter conductive pili as a protective cellular mechanism

“…The formation of a mononuclear U(IV) phase has also been reported for other bacteria of relevance to U bioremediation (34,35), yet contrasts with earlier reports of uraninite formation by Geobacter spp. (10,36). The chemical composition of the medium can influence the nature of the reduced U mineral (34).…”

Oxidative Dissolution of Biogenic Uraninite in Groundwater at Old Rifle, CO

“…The observed UÀU distances, and coordination numbers (CNs) are consistent with biogenic uraninite. 10,30 Because crystallite size does not vary significantly, the increase in the 3.8 Å (R+dR) UÀU FT frequency following submersion in the Rifle aquifer indicates that the particles became more ordered after reaction in groundwater, implying increased stability.…”

“…Biogenic uraninite is almost universally reported to be a nanoparticulate (2À5 nm) solid, although it tends to form larger agglomerates 15,16 and exhibits structural similarity even when produced by a phylogenetically diverse group of organisms. 10 Whereas the oxidative dissolution of biogenic uraninite has been studied in the laboratory (e.g., refs 17À21), its behavior under aquifer conditions has not been investigated. The rates of uraninite oxidation in groundwater are expected to differ from those measured under well-stirred laboratory conditions because of the sensitivity of uraninite reaction rates to the presence of various trace groundwater solutes 22 and to diffusionlimited conditions in aquifer pore spaces.…”