U(VI) Reduction to Mononuclear U(IV) by Desulfitobacterium Species

Fletcher, Kelly E.; Boyanov, Maxim I.; Thomas, Sara H.; Wu, Qingzhong; Kemner, Kenneth M.; Löffler, Frank E.

doi:10.1021/es903636c

Cited by 171 publications

(153 citation statements)

References 44 publications

Supporting

Mentioning

141

Contrasting

Order By: Relevance

“…The P coordination and the generalized periplasmic mineralization observed in the PilA − mutant cells suggest that U(VI) permeated deep and fast into the cell envelope, where it formed carboxyl and phosphoryl-coordinated complexes with periplasmic proteins and the peptidoglycan layer (30,31) and membrane phospholipids (33), respectively. 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).…”

Section: Discussion Physiological Relevance Of the Extracellular Redumentioning

confidence: 67%

“…(10,36). The chemical composition of the medium can influence the nature of the reduced U mineral (34). We used a bicarbonate buffer and conditions used in previous studies with G. sulfurreducens (13), whereas studies reporting uraninite formation used PIPES-buffered solutions (36) or bicarbonatebuffered uncontaminated groundwater (10).…”

Section: Discussion Physiological Relevance Of the Extracellular Redumentioning

confidence: 99%

See 1 more Smart Citation

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

Cologgi

Lampa-Pastirk

Speers

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

221

239

View full text Add to dashboard Cite

The in situ stimulation of Fe(III) oxide reduction by Geobacter bacteria leads to the concomitant precipitation of hexavalent uranium [U(VI)] from groundwater. Despite its promise for the bioremediation of uranium contaminants, the biological mechanism behind this reaction remains elusive. Because Fe(III) oxide reduction requires the expression of Geobacter 's conductive pili, we evaluated their contribution to uranium reduction in Geobacter sulfurreducens grown under pili-inducing or noninducing conditions. A pilin-deficient mutant and a genetically complemented strain with reduced outer membrane c -cytochrome content were used as controls. Pili expression significantly enhanced the rate and extent of uranium immobilization per cell and prevented periplasmic mineralization. As a result, pili expression also preserved the vital respiratory activities of the cell envelope and the cell's viability. Uranium preferentially precipitated along the pili and, to a lesser extent, on outer membrane redox-active foci. In contrast, the pilus-defective strains had different degrees of periplasmic mineralization matching well with their outer membrane c -cytochrome content. X-ray absorption spectroscopy analyses demonstrated the extracellular reduction of U(VI) by the pili to mononuclear tetravalent uranium U(IV) complexed by carbon-containing ligands, consistent with a biological reduction. In contrast, the U(IV) in the pilin-deficient mutant cells also required an additional phosphorous ligand, in agreement with the predominantly periplasmic mineralization of uranium observed in this strain. These findings demonstrate a previously unrecognized role for Geobacter conductive pili in the extracellular reduction of uranium, and highlight its essential function as a catalytic and protective cellular mechanism that is of interest for the bioremediation of uranium-contaminated groundwater.

show abstract

Section: Discussion Physiological Relevance Of the Extracellular Redumentioning

confidence: 67%

Section: Discussion Physiological Relevance Of the Extracellular Redumentioning

confidence: 99%

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

Cologgi

Lampa-Pastirk

Speers

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

221

239

View full text Add to dashboard Cite

show abstract

“…Although bacteria can enzymatically reduce uranium, abiotic processes leading to uranium reduction in the environment are also likely to be important. While studies have considered uraninite to be the primary product of uranium reduction (Langmuir 1978), evidence from this and other (Fletcher et al, 2010;Bernier-Latmani et al, 2010) work strongly suggests the formation of non-uraninite species of reduced uranium including monomeric U(IV) species. Importantly, the presence of structural or sorbed phosphate inhibits uraninite formation.…”

Section: Conclusion and Environmental Implicationsmentioning

confidence: 76%

“…Finally, batch uranium reduction experiments with Gram positive, spore-forming bacteria Desulfotomaculum reducens MI-1 and Clostridium acetobutylicum as well as the Gram negative bacterium S. oneidensis MR-1 carrying the reduction in a similar medium as the Gram positive bacteria resulted in the formation of monomeric U(IV) (Bernier-Latmani et al, 2010). Likewise, Fletcher et al (2010) reported formation of mononuclear U(IV) by Desulfitobacterium spp.…”

Section: Discussionmentioning

confidence: 89%

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

Veeramani

Alessi

Suvorova

et al. 2011

Geochimica et Cosmochimica Acta

138

122

View full text Add to dashboard Cite

Reductive immobilization of uranium by the stimulation of dissimilatory metal-reducing bacteria (DMRB) has been investigated as a remediation strategy for subsurface U(VI) contamination. In those environments, DMRB may utilize a variety of electron acceptors, such as ferric iron which can lead to the formation of reactive biogenic Fe(II) phases. These biogenic phases could potentially mediate abiotic U(VI) reduction. In this work, the DMRB Shewanella putrefaciens strain CN32 was used to synthesize two biogenic Fe(II)-bearing minerals: magnetite (a mixed Fe(II)-Fe(III) oxide) and vivianite (an Fe(II)-phosphate). Analysis of abiotic redox interactions between these biogenic minerals and U(VI) showed that both biogenic minerals reduced U(VI) completely. XAS analysis indicates significant differences in speciation of the reduced uranium after reaction with the two biogenic Fe(II)-bearing minerals. While biogenic magnetite favored the formation of structurally ordered, crystalline UO 2 , biogenic vivianite led to the formation of a monomeric U(IV) species lacking U-U associations in the corresponding EXAFS spectrum. To investigate the role of phosphate in the formation of monomeric U(IV) such as sorbed U(IV) species complexed by mineral surfaces, versus a U(IV) mineral, uranium was reduced by biogenic magnetite that was pre-sorbed with phosphate. XAS analysis of this sample also revealed the formation of monomeric U(IV) species suggesting that the presence of phosphate hinders formation of UO 2 . This work shows that U(VI) reduction products formed during in situ biostimulation can be influenced by the mineralogical and geochemical composition of the surrounding environment, as well as by the interfacial solute-solid chemistry of the solid-phase reductant.

show abstract

“…Bernier-Latmani et al, 2010;Fletcher et al, 2010;Veeramani et al, 2011;Sharp et al, 2011;Cologgi et al, 2011). The species may form along with the crystalline U(IV) phase uraninite, UO 2 (s), in laboratory experiments and in field-scale remediation efforts that aim to reduce U(VI) to less soluble U(IV) species.…”

Section: Introductionmentioning

confidence: 99%

Beam-induced oxidation of monomeric U(IV) species

Alessi

Uster

Borca

et al. 2012

J Synchrotron Radiat

View full text Add to dashboard Cite

UraniumLIII-edge X-ray absorption spectroscopy is often used to probe the oxidation state and coordination of uranium in environmental samples, and micrometre-sized beams can be used to spatially map the distribution of uranium relative to other elements. Here a variety of uranium-containing environmental samples are analyzed at both microbeam and larger beam sizes to determine whether reoxidation of U(IV) occurred. Monomeric U(IV), a recently discovered product of U(VI) reduction by microbes and certain iron-bearing minerals at uranium-contaminated field sites, was found to be reoxidized during microbeam (3 µm × 2 µm) analysis of biomass and sediments containing the species but not at larger beam sizes. Thus, care must be taken when using X-ray microprobes to analyze samples containing monomeric U(IV).

show abstract

U(VI) Reduction to Mononuclear U(IV) by Desulfitobacterium Species

Cited by 171 publications

References 44 publications

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

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

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

Beam-induced oxidation of monomeric U(IV) species

Contact Info

Product

Resources

About