Electron transfer at the cell–uranium interface in <i>Geobacter</i> spp.

Reguera, Gemma

doi:10.1042/bst20120162

Cited by 24 publications

(12 citation statements)

References 50 publications

(93 reference statements)

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“…Biochemical evidence suggests that the reductase transfers one electron to form U(V), which then disproportionates to U(VI) and U(IV), rather than executing a two electron transfer (Renshaw et al, 2005;Großmann et al, 2007). An additional pathway for microbial U(VI) reduction has been observed in Geobacter species, utilizing extracelluar conductive pili (Cologgi et al, 2011;Reguera, 2012). This pathway enhanced the rate and extent of U reduction per cell and prevented accumulation of reduced U minerals inside the cell, protecting the cell's viability.…”

Section: Geomicrobiology Of U Oxidation and Reduction: Enzymatically mentioning

confidence: 99%

Biogeochemical aspects of uranium mineralization, mining, milling, and remediation

Campbell¹,

Gallegos²,

Landa

2015

Applied Geochemistry

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aspects of uranium mineralization, mining, milling, and remediation" (2014 U is overwhelmingly the most abundant at greater than 99% of the total mass of U. Prior to the 1940s, U was predominantly used as a coloring agent, and U-bearing ores were mined mainly for their radium (Ra) and/or vanadium (V) content; the bulk of the U was discarded with the tailings (Finch et al., 1972). Once nuclear fission was discovered, the economic importance of U increased greatly. The mining and milling of U-bearing ores is the first step in the nuclear fuel cycle, and the contact of residual waste with natural water is a potential source of contamination of U and associated elements to the environment. Uranium is mined by three basic methods: surface (open pit), underground, and solution mining (in situ leaching or in situ recovery), depending on the deposit grade, size, location, geology and economic considerations (Abdelouas, 2006). Solid wastes at U mill tailings (UMT) sites can include both standard tailings (i.e., leached ore rock residues) and solids generated on site by waste treatment processes. The latter can include sludge or ''mud'' from neutralization of acidic mine/mill effluents, containing Fe and a range of coprecipitated constituents, or barium sulfate precipitates that selectively remove Ra (e.g., Carvalho et al., 2007). In this chapter, we review the hydrometallurgical processes by which U is extracted from ore, the biogeochemical processes that can affect the fate and transport of U and associated elements in the environment, and possible remediation strategies for site closure and aquifer restoration. This paper represents the fourth in a series of review papers from the U.S. Geological Survey (USGS) on geochemical aspects of UMT management that span more than three decades. The first paper (Landa, 1980) in this series is a primer on the nature of tailings and radionuclide mobilization from them. The second paper (Landa, 1999) includes coverage of research carried out under the U.S. Department of Energy's Uranium Mill Tailings Remedial Action Program (UMTRA). The third paper (Landa, 2004) reflects the increased focus of researchers on biotic effects in UMT environs. This paper expands the focus to U mining, milling, and remedial actions, and includes extensive coverage of the increasingly important alkaline in situ recovery and groundwater restoration.Ó 2014 Published by Elsevier Ltd.

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Section: Geomicrobiology Of U Oxidation and Reduction: Enzymatically mentioning

confidence: 99%

Biogeochemical aspects of uranium mineralization, mining, milling, and remediation

Campbell¹,

Gallegos²,

Landa

2015

Applied Geochemistry

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“…The suggestion that electrons are directly transferred from the conductive pili of Geobacter sulfurreducens to U(VI) (3,4) contrasts with the finding that pili are not required for the reduction of other soluble extracellular electron acceptors, such as Fe(III) citrate or the humic substances analog anthraquinone-2,6-disulfonate (AQDS) (5,6).…”

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confidence: 91%

U(VI) Reduction by Diverse Outer Surface c -Type Cytochromes of Geobacter sulfurreducens

Orellana

Leavitt

Comolli

et al. 2013

Appl Environ Microbiol

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Early studies with Geobacter sulfurreducens suggested that outer-surface c-type cytochromes might play a role in U(VI) reduction, but it has recently been suggested that there is substantial U(VI) reduction at the surface of the electrically conductive pili known as microbial nanowires. This phenomenon was further investigated. A strain of G. sulfurreducens, known as Aro-5, which produces pili with substantially reduced conductivity reduced U(VI) nearly as well as the wild type, as did a strain in which the gene for PilA, the structural pilin protein, was deleted. In order to reduce rates of U(VI) reduction to levels less than 20% of the wild-type rates, it was necessary to delete the genes for the five most abundant outer surface c-type cytochromes of G. sulfurreducens. X-ray absorption near-edge structure spectroscopy demonstrated that whereas 83% ؎ 10% of the uranium associated with wild-type cells correspond to U(IV) after 4 h of incubation, with the quintuple mutant, 89% ؎ 10% of uranium was U(VI). Transmission electron microscopy and X-ray energy dispersion spectroscopy revealed that wild-type cells did not precipitate uranium along pili as previously reported, but U(IV) was precipitated at the outer cell surface. These findings are consistent with those of previous studies, which have suggested that G. sulfurreducens requires outer-surface c-type cytochromes but not pili for the reduction of soluble extracellular electron acceptors.

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“…Micrographs of uranium‐reducing cells show some spots of uranium mineralization on the cell surface, which could correspond to reductive foci of outer membrane c‐Cyts (Cologgi et al ., 2011). However, in contrast to the positive correlation between piliation and extracellular uranium mineralization (Cologgi et al ., 2011), a reverse correlation exists between the outer membrane haem content and the amount of uranium that is mineralized outside the cell and prevented from traversing the outer membrane (Reguera, 2012). This suggests that outer membrane c‐Cyts provide secondary reductive foci on the outer membrane, yet their contribution to mineralization is small compared to the conductive T4P.…”

Section: A Nanowire Pathway For Metal Reductionmentioning

confidence: 99%

Harnessing the power of microbial nanowires

Reguera

2018

Microbial Biotechnology

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SummaryThe reduction of iron oxide minerals and uranium in model metal reducers in the genus Geobacter is mediated by conductive pili composed primarily of a structurally divergent pilin peptide that is otherwise recognized, processed and assembled in the inner membrane by a conserved Type IVa pilus apparatus. Electronic coupling among the peptides is promoted upon assembly, allowing the discharge of respiratory electrons at rates that greatly exceed the rates of cellular respiration. Harnessing the unique properties of these conductive appendages and their peptide building blocks in metal bioremediation will require understanding of how the pilins assemble to form a protein nanowire with specialized sites for metal immobilization. Also important are insights into how cells assemble the pili to make an electroactive matrix and grow on electrodes as biofilms that harvest electrical currents from the oxidation of waste organic substrates. Genetic engineering shows promise to modulate the properties of the peptide building blocks, protein nanowires and current‐harvesting biofilms for various applications. This minireview discusses what is known about the pilus material properties and reactions they catalyse and how this information can be harnessed in nanotechnology, bioremediation and bioenergy applications.

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Electron transfer at the cell–uranium interface in Geobacter spp.

Cited by 24 publications

References 50 publications

Biogeochemical aspects of uranium mineralization, mining, milling, and remediation

Biogeochemical aspects of uranium mineralization, mining, milling, and remediation

U(VI) Reduction by Diverse Outer Surface c -Type Cytochromes of Geobacter sulfurreducens

Harnessing the power of microbial nanowires

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