Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Williamson, Adam; Morris, Katherine; Law, Gareth T. W.; Rizoulis, Athanasios; Charnock, John; Lloyd, Jonathan R.

doi:10.1021/es5017125

Cited by 37 publications

(47 citation statements)

References 51 publications

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“…Interestingly, sulfate removal was also observed by day 7, suggesting sulfate reduction was occurring in these systems (Fig.1). This is in contrast to systems maintained at pH 10 ( Williamson et al, 2014), where sulfate reduction is energetically unfavourable (Rizoulis et al, 2012), and highlights the potential for localized acidification due to biogeochemical processes in radioactive waste disposal. In the systems with added Fe(III), complete nitrate removal occurred by day 3 and nitrite concentrations then increased (Fig.…”

Section: Biogeochemistry In Sediment Microcosmsmentioning

confidence: 75%

“…The pyrosequencing run was performed at The University of Manchester sequencing facility using a Roche 454 Life Sciences GS Junior system. Details of the PCR procedure and pyrosequencing analysis have been previously outlined (Williamson et al, 2014). The pyrosequencing reads from this study will be deposited in the NCBI Sequence Read Archive (SRA).…”

Section: S Rrna Gene Amplicon Pyrosequencing and Data Analysismentioning

confidence: 99%

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Microbially mediated reduction of Np(V) by a consortium of alkaline tolerant Fe(III)-reducing bacteria

et al. 2015

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Neptunium-237 will be present in radioactive wastes over extended time periods due to its long half-life (2.13 × 106 years). Understanding its behaviour under conditions relevant to radioactive waste disposal is therefore of particular importance. Here, microcosm experiments were established using sediments from a legacy lime workings with high-pH conditions as an analogue of cementitious intermediate-level radioactive waste disposal. To probe the influence of Fe biogeochemistry on Np(V) in these systems, additional Fe(III) (as ferrihydrite) was added to select experiments. Biogeochemical changes were tracked in experiments with low levels of Np(V) (20 Bq ml–1; 3.3 μM), whilst parallel higher concentration systems (2.5 KBq ml–1; 414 μM) allowed X-ray absorption spectroscopy. As expected, microbial reduction processes developed in microbially-active systems with an initial pH of 10; however, during microbial incubations the pH dropped from 10 to ∼7, reflecting the high levels of microbial metabolism occurring in these systems. In microbially-active systems without added Fe(III), 90% sorption of Np(V) occurred within one hour with essentially complete removal by one day. In the ferrihydrite-amended systems, complete sorption of Np(V) to ferrihydrite occurred within one hour. For higher-activity sediments, X-ray absorption spectroscopy (XAS) at end points where Fe(II) ingrowth was observed confirmed that complete reductive precipitation of Np(V) to Np(IV) had occurred under similar conditions to low-level Np experiments. Finally, pre-reduced, Fe(III)-reducing sediments, with and without added Fe(III) and held at pH 10, were spiked with Np(V). These alkaline pre-reduced sediments showed significant removal of Np to sediments, and XAS confirmed partial reduction to Np(IV) with the no Fe system, and essentially complete reduction to Np(IV) in the Fe(III)-enriched systems. This suggested an indirect, Fe(II)-mediated pathway for Np(V) reduction under alkaline conditions. Microbial analyses using 16S rRNA gene pyrosequencing suggested a role for alkali-tolerant, Gram-positive Firmicutes in coupled Fe(III) reduction and Np immobilization in these experiments.

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Section: Biogeochemistry In Sediment Microcosmsmentioning

confidence: 75%

Section: S Rrna Gene Amplicon Pyrosequencing and Data Analysismentioning

confidence: 99%

Microbially mediated reduction of Np(V) by a consortium of alkaline tolerant Fe(III)-reducing bacteria

et al. 2015

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“…A vast number of dissimilatory iron reducing bacteria have been identified in soil environments (Wang et al 2009;Yuan et al 2016), and almost all microorganisms capable of reducing Fe(III) can also reduce humic substances (including AQDS) (Lovley et al 1999). It was found that humic substances including AQDS promoted the reduction of Fe(III) (oxyhydr)oxides driven by alkaliphilic bacteria isolated from extreme environments (pH 10.0 microbial fuel cells) and in uranium-contaminated sediments of pH 10.0-10.5 (Ma et al 2012;Wu et al 2013;Williamson et al 2014). The alkaliphilic bacteria could not represent microorganisms in natural soils and it is still ambiguous whether humic substance-mediated Fe(III) reduction is pervasive by common microorganisms in alkaline soils.…”

Section: Introductionmentioning

confidence: 99%

Electron shuttle-mediated microbial Fe(III) reduction under alkaline conditions

Wang

Sun

et al. 2017

J Soils Sediments

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Purpose: Extracellular Fe(III) reduction plays an important role in a variety of biogeochemical processes. Several mechanisms for microbial Fe(III) reduction in pH-neutral environments have been proposed, but pathways of microbial Fe(III) reduction within alkaline conditions have not been clearly identified. Alkaline soils are vastly distributed; thus, a better understanding of microbial Fe(III) reduction under alkaline conditions is of significance. The purpose of this study is to explore the dominant mechanism of bacterial iron reduction in alkaline environments. Materials and methods: We used antraquinone-2,6-disulfonate (AQDS) as a representative of quinone moities of humic substances and elemental sulfur and sulfate as sulfur species to investigate the potential role of humic substances and sulfur species in mediating microbial Fe(III) reduction in alkaline environments. We carried out thermodynamic calculations to predict the ability of bacteria to reduce Fe(III) (oxyhydr)oxides under alkaline conditions and the ability of AQDS and sulfur species to serve as electron acceptors for microbial anaerobic respiration in an assumed alkaline soil environments. A series of incubation experiments with two model dissimilatory metal reducing bacteria, Shewanella oneidensis MR-1 and Geobacter sulfurreducens PCA as well as mixed bacteria enriched from a soil were performed to confirm the contribution of AQDS and sulfur species to Fe(III) reduction under alkaline conditions. Results and discussion: Based on thermodynamic calculations, we predicted that, under alkaline conditions, the enzymatic reduction of Fe(III) (oxyhydr)oxides would be thermodynamically feasible but very weak. In our incubation experiments, the reduction of ferrihydrite by anaerobic cultures of Shewanella oneidensis MR-1, Geobacter sulfurreducens PCA or microbes enriched from a soil was significantly increased in the presence of S0 or AQDS. Notably, AQDS contributed more to promoting Fe(III) reduction as a soluble electron shuttle than S0 did under the alkaline conditions probably because of different mechanisms of microbial utilization of AQDS and S0. Conclusions: These results suggest that microbial reduction of Fe(III) (oxyhydr)oxides under alkaline conditions may proceed via a pathway mediated by electron shuttles such as AQDS and S0. Considering the high ability of electron shuttling and vast distribution of humic substances, we suggest that humic substance-mediated Fe(III) reduction may potentially be the dominant mechanism for Fe(III) reduction in alkaline environments

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“…Recently it was shown that a clear succession of electron acceptor utilization existed in alkaline microcosm cultures up to pH 11, as rapid nitrate reduction was followed by slower soluble Fe(III)-citrate, insoluble Fe(III)-oxyhydroxide, and sulfate reduction (Rizoulis et al 2012). Further sediment microcosm studies from our group have also shown that alkaline bioreduction of Fe(III)-oxyhydroxide can lead to the formation of magnetite (Williamson et al 2013) and that microbially mediated reduction of U(VI) can occur at pH 10 (Williamson et al 2014).…”

Section: Potential For Metal Reduction At Alkaline Phmentioning

confidence: 74%

Bacterial Diversity in the Hyperalkaline Allas Springs (Cyprus), a Natural Analogue for Cementitious Radioactive Waste Repository

Rizoulis

Milodowski

Morris

et al. 2016

Geomicrobiology Journal

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The biogeochemical gradients that will develop across the interface between a highly alkaline cementitious geological disposal facility for intermediate level radioactive waste and the geosphere are poorly understood. In addition, there is a paucity of information about the microorganisms that may populate these environments and their role in biomineralization, gas consumption and generation, metal cycling, and on radionuclide speciation and solubility. In this study, we investigated the phylogenetic diversity of indigenous microbial communities and their potential for alkaline metal reduction in samples collected from a natural analogue for cementitious radioactive waste repositories, the hyperalkaline Allas Springs (pH up to 11.9), Troodos Mountains, Cyprus. The site is situated within an ophiolitic complex of ultrabasic rocks that are undergoing active low-temperature serpentinization, which results in hyperalkaline conditions. 16S rRNA cloning and sequencing showed that phylogenetically diverse microbial communities exist in this natural high pH environment, including Hydrogenophaga species. This indicates that alkali-tolerant hydrogen-oxidizing microorganisms could potentially colonize an alkaline geological repository, which is predicted to be rich in molecular H 2 , as a result of processes including steel corrosion and cellulose biodegradation within the wastes. Moreover, microbial metal reduction was confirmed at alkaline pH in this study by enrichment microcosms and by pure cultures of bacterial isolates affiliated to the Paenibacillus and Alkaliphilus genera. Overall, these data show that a diverse range of microbiological processes can occur in high pH environments, consistent with those expected during the geodisposal of intermediate level waste. Many of these, including gas metabolism and metal reduction, have clear implications for the long-term geological disposal of radioactive waste.

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Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Cited by 37 publications

References 51 publications

Microbially mediated reduction of Np(V) by a consortium of alkaline tolerant Fe(III)-reducing bacteria

Microbially mediated reduction of Np(V) by a consortium of alkaline tolerant Fe(III)-reducing bacteria

Electron shuttle-mediated microbial Fe(III) reduction under alkaline conditions

Bacterial Diversity in the Hyperalkaline Allas Springs (Cyprus), a Natural Analogue for Cementitious Radioactive Waste Repository

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