The biomineralization process of uranium(VI) by Saccharomyces cerevisiae - transformation from amorphous U(VI) to crystalline chernikovite

Enhanced microbial remediation of uranium tailings through red soil utilization

Seepage of uranium tailings has become a focus of attention in the uranium mining and metallurgy industry, and in-situ microbial remediation is considered an effective way to treat uranium pollution. However, this method has the drawbacks of easy biomass loss and unstable remediation effect. To overcome these issues, spare red soil around the uranium mine was used to enhance the efficiency and stability of bioremediation. Furthermore, the bioremediation mechanism was revealed by employing XRD, FTIR, XPS, and 16S rRNA. The results showed that red soil, as a barrier material, had the adsorption potential of 8.21-148.00 mg U/kg soil, but the adsorption is accompanied by the release of certain acidic and oxidative substances. During the dynamic microbial remediation, red soil was used as a cover material to neutralize acidity, provide a higher reduction potential (<-200 mV), and increase the retention rate of microbial agent (19.06 mL/d) compared to the remediation group without red soil. In the presence of red soil, the anaerobic system could maintain the uranium concentration in the solution below 0.3 mg/L for more than 70 days. Moreover, the generation of new clay minerals driven by microorganisms was more conducive to the stability of uranium tailings. Through alcohol and amino acid metabolism of microorganisms, a reducing environment with reduced valence states of multiple elements (such as S2-, Fe2+, and U4+) was formed. At the same time, the relative abundance of functional microbial communities in uranium tailings improved in presence of red soil and Desulfovirobo, Desulfocapsa, Desulfosporosinus, and other active microbial communities reconstructed the anaerobic environment. The study provides a new two-in-one solution for treatment of uranium tailings and resource utilization of red soil through in-situ microbial remediation.

Bibliometric insights into the evolution of uranium contamination reduction research topics: Focus on microbial reduction of uranium

Confronting the threat of environment uranium pollution, decades of research have yielded advanced and significant findings in uranium bioremediation, resulting in the accumulation of tremendous amount of high-quality literature. In this study, we analyzed over 10,000 uranium reduction-related papers published from 1990 to the present in the Web of Science based on bibliometrics, and revealed some critical information on knowledge structure, thematic evolution and additional attention. Methods including contribution comparison, co-occurrence and temporal evolution analysis are applied. The results of the distribution and impact analysis of authors, sources, and journals indicated that the United States is a leader in this field of research and China is on the rise. The top keywords remained stable, primarily focused on chemicals (uranium, iron, plutonium, nitrat, carbon), characters (divers, surfac, speciat), and microbiology (microbial commun, cytochrome, extracellular polymeric subst). Keywords related to new strains, reduction mechanisms and product characteristics demonstrated the strongest uptrend, while some keywords related to mechanism and performance were clearly emerging in the past 5 years. Furthermore, the evolution of the thematic progression can be categorized into three stages, commencing with the discovery of the enzymatic reduction of hexavalent uranium to tetravalent uranium, developing in the groundwater remediation process at uranium-contaminated sites, and delving into the research on microbial reduction mechanisms of uranium. For future research, enhancing the understanding of mechanisms, improving uranium removal performance, and exploring practical applications can be considered. This study provides unique insights into microbial uranium reduction research, providing valuable references for related studies in this field.

Utilization of nickel-graphite electrode as an electron donor for high-efficient microbial removal of solved U(VI) mediated by Leifsonia sp

Enzymatically catalyzed reduction of metals by bacteria has potential application value to uranium-mine wastewater. However, its practical implementation has long been restricted by its intrinsic drawbacks such as low efficiency and long treatment-time. This study aims to explore the effect of electrodes on U (VI) removal efficiency by a purified indigenous bacteria isolated from a uranium mining waste pile in China. The effects of current intensity, pH, initial U (Ⅵ) concentration, initial dosage of bacteria and contact time on U (Ⅵ) removal efficiency were investigated via static experiments. The results show that U(VI) removal rate was stabilized above 90% and the contact time sharply shortened within 1 h when utilized nickel-graphite electrode as an electron donor. Over the treatment ranges investigated maximum removal of U (Ⅵ) was 96.04% when the direct current was 10 mA, pH was 5, initial U (Ⅵ) concentration was 10 mg/L, and dosage of Leifsonia sp. was 0.25 g/L. In addition, it is demonstrated that U (VI) adsorption by Leifsonia sp. is mainly chemisorption and/or reduction as the quasi-secondary kinetics is more suitable for fitting the process. FTIR results indicated that amino, amide, aldehyde and phosphate -containing groups played a role in the immobilization of U (VI) more or less. SEM and EDS measurements revealed that U appeared to be more obviously aggregated on the surface of cells. A plausible explanation for this, supported by XPS, is that U (VI) was partially reduced to U (IV) by direct current then precipitated on the cells surface. These observations reveal that Nickel-graphite electrode exhibited good electro-chemical properties and synergistic capacity with Leifsonia sp. which potentially provides a new avenue for uranium enhanced removal/immobilization by indigenous bacteria.

Enhanced indigenous consortia for the remediation of uranium-contaminated groundwater by bioaugmentation: Reducing and phosphate-solubilizing consortia

To investigate the strengthening effects and mechanisms of bioaugmentation on the microbial remediation of uranium-contaminated groundwater via bioreduction coupled to biomineralization, two exogenous microbial consortia with reducing and phosphate-solubilizing functions were screened and added to uranium-contaminated groundwater as the experimental groups (group B, reducing consortium added; group C, phosphate-solubilizing consortium added). β-glycerophosphate (GP) was selected to stimulate the microbial community as the sole electron donor and phosphorus source. The results showed that bioaugmentation accelerated the consumption of GP and the proliferation of key functional microbes in groups B and C. In group B, Dysgonomonas, Clostridium_sensu_stricto_11 and Clostridium_sensu_stricto_13 were the main reducing bacteria, and Paenibacillus was the main phosphate-solubilizing bacteria. In group C, the microorganisms that solubilized phosphate were mainly unclassified_f_Enterobacteriaceae. Additionally, bioaugmentation promoted the formation of unattached precipitates and alleviated the inhibitory effect of cell surface precipitation on microbial metabolism. As a result, the formation rate of U-phosphate precipitates and the removal rates of aqueous U(VI) in both groups B and C were elevated significantly after bioaugmentation. The U(VI) removal rate was poor in the control group (group A, with only an indigenous consortium). Propionispora, Sporomusa and Clostridium_sensu_stricto_11 may have played an important role in the removal of uranium in group A. Furthermore, the addition of a reducing consortium promoted the reduction of U(VI) to U(IV), and immobilized uranium existed in the form of U(IV)-phosphate and U(VI)-phosphate precipitates in group B. In contrast, U was present mainly as U(VI)-phosphate precipitates in groups A and C. Overall, bioaugmentation with an exogenous consortium resulted in the rapid removal of uranium from groundwater and the formation of U-phosphate minerals and served as an effective strategy for improving the treatment of uranium-contaminated groundwater in situ.

Uranium speciation and distribution on the surface of Shewanella putrefaciens in the presence of inorganic phosphate and zero-valent iron under anaerobic conditions

Shewanella putrefaciens (S. putrefaciens) is one of the main microorganisms in soil bioreactors, which mainly immobilizes uranium through reduction and mineralization processes. However, the effects of elements such as phosphorus and ZVI, which may be present in the actual environment, on the mineralization and reduction processes are still not clearly understood and the environment is mostly in the absence of oxygen. In this study, we ensure that all experiments are performed in an anaerobic glove box, and we elucidate through a combination of macroscopic experimental findings and microscopic characterization that the presence of inorganic phosphates enhances the mineralization of uranyl ions on the surface of S. putrefaciens, while zero-valent iron (ZVI) facilitates the immobilization of uranium by promoting the reduction of uranium by S. putrefaciens. Interestingly, when inorganic phosphates and ZVI co-exist, both the mineralization and reduction of uranium on the bacterial surface are simultaneously enhanced. However, these two substances exhibit a certain degree of antagonism in terms of uranium immobilization by S. putrefaciens. Furthermore, it is found that the influence of pH on the mineralization and reduction of uranyl ions is far more significant than that of inorganic phosphates and ZVI. This study contributes to a better understanding of the environmental fate of uranium in real-world settings and provides valuable theoretical support for the bioremediation and risk assessment of uranium contamination.

Extracellular biomineralization of uranium and its toxicity alleviation to Bacillus thuringiensis X-27

Uranium biomineralization can slow uranium migration in the environment and thus prevent it from further contaminating the surroundings. Investigations into the uranium species, pH, inorganic phosphate (Pi) concentration, and microbial viability during biomineralization by microorganisms are crucial for understanding the mineralization mechanism. In this study, Bacillus thuringiensis X-27 was isolated from soil contaminated with uranium and was used to investigate the formation process of uranium biominerals induced by X-27. The results showed that as biomineralization proceeded, amorphous uranium-containing deposits were generated and transformed into crystalline minerals outside cells, increasing the overall concentration of uramphite. This is a cumulative rather than abrupt process. Notably, B. thuringiensis X-27 precipitated uranium outside the cell surface within 0.5 h, while the release of Pi into the extracellular environment and the change of pH to alkalescence further promoted the formation of uramphite. In addition, cell viability determination showed that the U(VI) biomineralization induced by B. thuringiensis X-27 was instrumental in alleviating the toxicity of U(VI) to cells. This work offers insight into the mechanism of U(VI) phosphate biomineralization and is a reference for bioremediation-related studies.

Synergy of surface adsorption and intracellular accumulation for removal of uranium with Stenotrophomonas sp: Performance and mechanisms

Uranium is well-known to have serious adverse effects on the ecological environment and human health. Bioremediation stands out among many remediation methods owing to its being economically feasible and environmentally friendly. This study reported a great promising strategy for eliminating uranium by Stenotrophomonas sp. CICC 23833 in the aquatic environment. The bacterium demonstrated excellent uranium adsorption capacity (q_max = 392.9 mg/g) because of the synergistic effect of surface adsorption and intracellular accumulation. Further analysis revealed that hydroxyl, carboxyl, phosphate groups and proteins of microorganisms were essential in uranium adsorption. Intracellular accumulation was closely related to cellular activity, and the efficiency of uranium processing by the permeabilized bacterial cells was significantly improved. In response to uranium stress, the bacterium was found to release multiple ions in conjunction with uranium adsorption, which facilitates the maintenance of bacterial life activities and the conversion of uranyl to precipitates. These above results indicated that Stenotrophomonas sp. Had great potential application value for the remediation of uranium.

Cellular transport of uranium and its cytotoxicity effects on CHO-k1 cells

Uranium is a radioactive heavy metal and a significant public health concern; however, its associated underlying toxicological mechanisms remain largely unknown. In this work, the uptake and efflux processes of uranium in CHO-k1 cells were studied and the cytotoxicity effects were explored. It was found that both the uptake and efflux processes took place rapidly and half of the internalized uranium was expelled within 8 h. The uranium exposure caused a decrease of cell viability and adhesion ability in a dose-dependent manner and blocked the cell cycle at the G1 stage. In addition, gene expression analysis revealed relative changes in the transcription of metabolism related genes. Further studies revealed that the cytotoxicity of uranium could be alleviated by exposing cells to a lower temperature or by the addition of amantadine-HCl, an endocytosis inhibitor. Interestingly, after uranium exposure, needle-like precipitates were observed in both intracellular and extracellular regions. These findings collectively suggest that the cellular transport of uranium is a rapid process that disturbs cell metabolism and induces cytotoxicity, and this impact could be reduced by slowing down endocytic processes.

Enhanced immobilization of uranium(VI) during the conversion of microbially induced calcite to hydroxylapatite

Carbonate-bound uranium (U) is critical in controlling the migration of U in circumneutral to alkaline conditions. The potential release risk of carbonate-bound U should be concerned due to the contribution of mineral replacement. Herein, we explored the fate of U during the conversion process from microbial-induced calcite to hydroxylapatite (HAP) and investigated the phase and morphology evolution of minerals and the immobilization efficiency, distribution, and stability of U. The results showed that most calcite could convert to HAP during the conversion process. The aqueous residual U was below 1.0 mg/L after U-HAP formation, and the U removal efficiencies were enhanced by 20.0-74.4% compared to the calcite precipitation process. XRD and TEM results showed that the products were a mixture of HAP and uramphite. The elemental mapping results showed that most U concentrated on uramphite while a handful of U distributed homogeneously in calcite and HAP matrixes. The stability test verified that U-bearing HAP decreased the U solubility by 98-100% relative to calcite due to the uramphite formation and U incorporation into HAP. Our findings demonstrated that the combinations of microbial-induced calcite precipitation and calcite-HAP conversion could facilitate the U immobilization in treating radioactive wastewater and soil.

New Insights Into Microbial Induced Calcium Carbonate Precipitation Using Saccharomyces cerevisiae

Saccharomyces cerevisiae plays an important role in the mineralization of many metal ions, but it is unclear whether this fungus is involved in the mineralization of calcium carbonate. In this study, S. cerevisiae was cultured under various conditions to explore its ability to perform microbially induced calcium carbonate precipitation (MICP). Organic acids, yeast extract, and low-carbon conditions were the factors influencing the biomineralization of calcium carbonate caused by S. cerevisiae, and biomolecules secreted by the fungus under different conditions could change the morphology, size, and crystal form of the biosynthesized mineral. In addition, transcriptome analysis showed that the oxidation of organic acids enhanced the respiration process of yeast. This implied that S. cerevisiae played a role in the formation of calcium carbonate through the mechanism of creating an alkaline environment by the respiratory metabolism of organic acids, which could provide sufficient dissolved inorganic carbon for calcium carbonate formation. These results provide new insights into the role of S. cerevisiae in biomineralization and extend the potential applications of this fungus in the future.

Highly efficient immobilization of environmental uranium contamination with Pseudomonas stutzeri by biosorption, biomineralization, and bioreduction

Uranium is a heavy metal with both chemotoxicity and radiotoxicity. Due to the increasing consumption of uranium, the remediation of uranium contamination and recovery of uranium from non-conventional approach is highly needed. Microorganism exhibits high potential for immobilization of uranium. This study for the first time isolated a marine Pseudomonas stutzeri strain MRU-UE1 with high uranium immobilization capacity of 308.72 mg/g, which is attributed to the synergetic mechanisms of biosorption, biomineralization, and bioreduction. The uranium is found to be immobilized in forms of tetragonal chernikovite (H₂(UO₂)₂(PO₄)₂·8H₂O) by biomineralization and CaU(PO₄)₂ by bioreduction under aerobic environment, which is rarely observed and would broaden the application of this strain in aerobic condition. The protein, phosphate group, and carboxyl group are found to be essential for the biosorption of uranium. In response to the stress of uranium, the strain produces inorganic phosphate group, which transformed soluble uranyl ion to insoluble uranium-containing precipitates, and poly-β-hydroxybutyrate (PHB), which is observed for the first time during the interaction between microorganism and uranium. In summary, P. stutzeri strain MRU-UE1 would be a promising alternative for environmental uranium contamination remediation and uranium extraction from seawater.

High-affinity iron and calcium transport pathways are involved in U(VI) uptake in the budding yeast Saccharomyces cerevisiae

Uranium (U) is a naturally-occurring radionuclide that is toxic for all living organisms. To date, the mechanisms of U uptake are far from being understood. Here we provide a direct characterization of the transport machineries capable of transporting U, using the yeast Saccharomyces cerevisiae as a unicellular eukaryote model. First, we evidenced a metabolism-dependent U transport in yeast. Then, competition experiments with essential metals allowed us to identify calcium, iron and copper entry pathways as potential routes for U uptake. The analysis of various metal transport mutants revealed that mutant affected in calcium (mid1Δ and cch1Δ) and Fe(III) (ftr1Δ) transport, exhibited highly reduced U uptake rates and accumulation, demonstrating the implication of the calcium channel Mid1/Cch1 and the iron permease Ftr1 in U uptake. Finally, expression of the Mid1 gene into the mid1Δ mutant restored U uptake levels of the wild type strain, underscoring the central role of the Mid1/Cch1 calcium channel in U absorption process in yeast. Our results also open up the opportunity for rapid screening of U-transporter candidates by functional expression in yeast, before their validation in more complex higher eukaryote model systems.

Mineralization induced by phosphorylated dry baker's yeast

We found the mineralization of Cu during long-term Cu2+ adsorption onto dry baker's yeast cells phosphorylated using sodium cyclo-triphosphate. Field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy confirmed that the elemental composition of minerals were copper, phosphorus, and oxygen. Synchrotron-based X-ray absorption fine structure showed that the local structure around Cu atoms deposited on the mineral was almost identical to that of commercial copper (II) phosphate Cu3(PO4)2∙3H2O. However, the crystallinity was low, and the structure was slightly distorted. Time profile analysis using FESEM revealed that copper phosphate mineralization was first apparent on Day 3 of adsorption, whereas mineral formation plateaued at around Day 7. It seems that mineralization occurs by the local saturation of phosphate and Cu2+ on the yeast cells. Mineralization of the rare earth ion Dy3+ was also demonstrated during long-term adsorption. Mineralization on phosphorylated yeast cells appears to follow a common path for various types of metal ions and provides a promising technique for metal recovery via irreversible adsorption.

High-efficient microbial immobilization of solved U(VI) by the Stenotrophomonas strain Br8

The environmental impact of uranium released during nuclear power production and related mining activity is an issue of great concern. Innovative environmental-friendly water remediation strategies, like those based on U biomineralization through phosphatase activity, are desirable. Here, we report the great U biomineralization potential of Stenotrophomonas sp. Br8 CECT 9810 over a wide range of physicochemical and biological conditions. Br8 cells exhibited high phosphatase activity which mediated the release of orthophosphate in the presence of glycerol-2-phosphate around pH 6.3. Mobile uranyl ions were bioprecipitated as needle-like fibrils at the cell surface and in the extracellular space, as observed by Scanning Transmission Electron Microscopy (STEM). Extended X-Ray Absorption Fine Structure (EXAFS) and X-Ray Diffraction (XRD) analyses showed the local structure of biogenic U precipitates to be similar to that of meta-autunite. In addition to the active U phosphate biomineralization process, the cells interact with this radionuclide through passive biosorption, removing up to 373 mg of U per g of bacterial dry biomass. The high U biomineralization capacity of the studied strain was also observed under different conditions of pH, temperature, etc. Results presented in this work will help to design efficient U bioremediation strategies for real polluted waters.

Effect of Leifsonia sp. on retardation of uranium in natural soil and its potential mechanisms

Uranium mining and milling activities for many years resulted in release of uranium into the adjoining soil in varying degrees. Bioremediation approaches (i.e., immobilization via the action of bacteria) resulting in uranium bearing solid is supposed as an economic and clean in-situ approach for the treatment of uranium contaminated sites. This study purposes to determine the immobilization efficiency of uranium in soil by Leifsonia sp. The results demonstrated that cells have a good proliferation ability under the stress of uranium and play a role in retaining uranium in soil. Residual uranium in active Leifsonia-medium group (66%) was higher than that in the controls, which was 31% in the deionised water control, 46% in the Leifsonia group, and 47% in the medium group, respectively. This indicated that Leifsonia sp. facilitates the immobilization efficiency of uranium in soil by converting part of the reducible and oxidizable fraction of uranium into the residual fraction. X-ray photoelectron fitting results showed that tetravalent states uranium existed in the soil samples, which indicated that the hexavalent uranium was converted into tetravalent by cells. This is the first report of effect of Leifsonia sp. on uranium immobilization in soil. The findings implied that Leifsonia sp. could, to some extent, prevent the migration and diffusion of uranium in soil by changing the chemical states into less toxicity and less risky forms.

Microbe-Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

Microbe-mediated mineralization is ubiquitous in nature, involving bacteria, fungi, viruses, and algae. These mineralization processes comprise calcification, silicification, and iron mineralization. The mechanisms for mineral formation include extracellular and intracellular biomineralization. The mineral precipitating capability of microbes is often harnessed for green synthesis of metal nanoparticles, which are relatively less toxic compared with those synthesized through physical or chemical methods. Microbe-mediated mineralization has important applications ranging from pollutant removal and nonreactive carriers, to other industrial and biomedical applications. Herein, the different types of microbe-mediated biomineralization that occur in nature, their mechanisms, as well as their applications are elucidated to create a backdrop for future research.

The utilization of biomineralization technique based on microbial induced phosphate precipitation in remediation of potentially toxic ions contaminated soil: A mini review

In recent years, many studies have been devoted to investigate the application of microbial induced phosphate precipitation (MIPP) process for potentially toxic element polluted soil remediation. MIPP biomineralization technique exhibits a great potential to efficiently remediate polluted soil considering its low cost, green and ecofriendly process, and simple in operation. This paper represented a review on the state of the art of polluted soil remediation based on MIPP technique. Briefly, certain defined criteria on targeted microbe selection was discussed; an overall review on the utilization of MIPP process for toxic ions biomineralization in soil was provided; influencing factors reported in the literature, such as pH, temperature, humic substances, coexisting ions, effective microbial population, and enzyme activity, were then comprehensively reviewed; finally; a special emphasis was given to enhance MIPP remediation performance in soil in future research.

Uranium biosorption mechanism model of protonated Saccharomyces cerevisiae

Further understanding absorption uranium mechanism of the regenerational biosorbent is very interesting in application of the biosorbent. The regeneration adsorbent of Saccharomyces cerevisiae biomass was made by hydrochloric acid. Using it to absorb uranium at low constant pH(2.50), accompanied with proton releasing the ratio almost 1:2 which is to be analyzed in this paper. The type and amount of functional groups in the biomass such as carboxyl, amino, phosphoryl were determined by Potentiometric titrations and FTIR analysis. Chemical modification showed that the contribution of functional groups to uranium adsorption was carboxyl, phosphoryl and amino in turn. Analysis of SEM-EDX and staining microscopy showed that uranium on the surface of cells did not exist in the form of precipitation at lower pH 2.98, but at higher pH 4.52. The effects of phosphorus release and pH on uranium species was analyzed by MINTEQ software 3.0. Based on the above boundary conditions of the model construction, a multi-site of functional groups model equation of ion exchange absorption mechanism was built in which the final uranium ion concentration and pH as functions. It could well describe the exchange equilibrium of proton with uranium ion at pH2.50 to pH4.00.

Advances on the toxicity of uranium to different organisms

The extensive application of radioactive element uranium (U) and its compounds in the nuclear industry has significantly increased the risk of exposure to the environment. Therefore, research on the safety risks and toxicity mechanisms of U exposure has received increasing attention. This paper reviews the toxic effects of U on different species under different conditions, and summarizes the potential toxicity mechanisms. Under the exposure of U, reactive oxygen species (ROS) produced in cells will damage membrane structure in cells, and inhibit respiratory chain reaction by reducing the production of NADH and ATP. It also induce the expression of apoptosis factors such as Bcl-2, Bid, Bax, and caspase family to cause apoptosis cascade reaction, leading to DNA degradation and cell death. We innovatively list some methods to reduce the toxicity of U because some microorganisms can precipitate uranyl ions through biomineralization or reduction processes. Our work provides a solid foundation for further risk assessment of U.

Gold Biomineralization on Bacterial Biofilms for Leaching of Au3+ Damages Eukaryotic Cells

Heavy metals not only pollute the environment but also are health and environmental hazard. Bacteria constitute inexpensive and eco-friendly material to eliminate and recycle heavy metals via biomineralization and biosorption. However, the effect of metal biomineralization in bacterial biofilms on the ecological balance of bacteria and infectious diseases is unclear. This study aimed to explore the interaction between a eukaryotic cell line HEK293T and mineralized Escherichia coli, using a model of gold biomineralization on E. coli biofilms (E. coli-Au). In our present model, bacterial activity was not disrupted and bacterial adhesion and invasion were enhanced. E. coli-Au invaded the cytoplasm and nuclei of HEK293T cells and damaged them via intracellular growth and multiplication. The present findings indicate that metal biomineralization in bacterial biofilms for leaching of heavy metal ions is hazardous to eukaryotic cells and even human health.

Effective capture of aqueous uranium from saline lake with magnesium-based binary and ternary layered double hydroxides

Uranium in saline lake brine is a nuclear resource that attracts worldwide attention. Relatively low concentrations (about 0.2 mg L^-1 to 30 mg L^-1) require high affinity for the capture materials. In this paper, magnesium binary layered double hydroxides (MgAl-LDH) and its Fe-induced ternary LDH (MgAlFe-LDH) were synthesized for the extraction of simulated concentrations of U(VI) in the saline lake brine system. Batch experiments have shown that both LDHs have strong affinity towards uranium. MgAl-LDH yielded of stronger affinity in lower U(VI) concentrations (0.2 mg L^-1 to 5 mg L^-1), while MgAlFe-LDH was at higher U(VI) concentrations (5 mg L^-1 to 30 mg L^-1). For current uranium extraction, the affinities of MgAl-LDH and MgAlFe-LDH are more than twice the maximum affinity of other LDHs and LDHs-based materials. Therefore, these two LDHs are suitable for U(VI) extraction with different concentration levels in saline lakes. The capture process followed the pseudo-second-order kinetics with fast adsorption speed, and the coexisting cations have little effect on the extraction rate. Research through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed the main adsorption mechanisms are surface complexation and the interlayer carbonate coprecipitation. This work provides a potential method for U(VI) extraction while reusing the waste magnesium resources in saline lake.

Kinetic and equilibrium of U(VI) biosorption onto the resistant bacterium Bacillus amyloliquefaciens

This study evaluated U(VI) biosorption properties by the resistant bacterium, Bacillus amyloliquefaciens, which was isolated from the soils with residual radionuclides. The effect of biosorption factors (uptake time, pH, ionic concentration, biosorbent dosage and temperature) on U(VI) removal was determined by batch experiments. The uptake processes were characterized by using SEM, FTIR, and XPS. The experimental data of U(VI) biosorption were fitted by the pseudo-second-order. The maximum uptake capacity was 179.5 mg/g at pH 6.0 by Langmuir model. The thermodynamic results: ΔG^о, ΔH^о and ΔS^о for uptake processes were calculated as -6.359 kJ/mol, 14.20 kJ/mol and 67.19 J/mol/K, respectively. The results showed that the biosorption of Bacillus amyloliquefaciens will be an ideal method to remove radionuclides.

Recovering metals from aqueous solutions by biosorption onto phosphorylated dry baker's yeast

Biosorption is a cost-effective and simple technique for removing heavy metals and rare earth elements from aqueous solution. Here, metals were recovered from aqueous solutions using phosphorylated dry baker’s yeast cells. The cells were phosphorylated using cyclo-triphosphate, Na₃P₃O₉. The total P content of the phosphorylated cells was ~1.0 mmol/g dry cell weight (DCW). The zeta potential of the phosphorylated cells was −45 mV, two times higher than for the non-phosphorylated cells. The strong negative charges of the phosphorylated cells allowed the cells to adsorb heavy metal ions such as Cd²⁺, Cu²⁺, Pb²⁺, and Zn²⁺, the adsorption capacities of which reached ~1.0 mmol/g DCW. This adsorption capacity was the highest level found in the previous studies using yeast dead biomass. The adsorbed metal ions were easily desorbed in 0.1 M HCl. The phosphorylated cells also adsorbed rare earth ions including Ce³⁺, Dy³⁺, Gd³⁺, La³⁺, Nd³⁺, Y³⁺, and Yb³⁺ with high efficiency. Furthermore, the phosphorylated yeast cells selectively adsorbed the rare earth ions (Nd³⁺ and Yb³⁺) from a solution containing heavy metals and rare earth ions because trivalent positively charged ions were adsorbed preferentially over divalent ions. Thus, phosphorylated yeast cells therefore have great potential for use as novel bioadsorbents. It is also expected that this technique can be applied to many microbial materials as well as yeast.

Metabolism-dependent bioaccumulation of uranium by Rhodosporidium toruloides isolated from the flooding water of a former uranium mine

Remediation of former uranium mining sites represents one of the biggest challenges worldwide that have to be solved in this century. During the last years, the search of alternative strategies involving environmentally sustainable treatments has started. Bioremediation, the use of microorganisms to clean up polluted sites in the environment, is considered one the best alternative. By means of culture-dependent methods, we isolated an indigenous yeast strain, KS5 (Rhodosporidium toruloides), directly from the flooding water of a former uranium mining site and investigated its interactions with uranium. Our results highlight distinct adaptive mechanisms towards high uranium concentrations on the one hand, and complex interaction mechanisms on the other. The cells of the strain KS5 exhibit high a uranium tolerance, being able to grow at 6 mM, and also a high ability to accumulate this radionuclide (350 mg uranium/g dry biomass, 48 h). The removal of uranium by KS5 displays a temperature- and cell viability-dependent process, indicating that metabolic activity could be involved. By STEM (scanning transmission electron microscopy) investigations, we observed that uranium was removed by two mechanisms, active bioaccumulation and inactive biosorption. This study highlights the potential of KS5 as a representative of indigenous species within the flooding water of a former uranium mine, which may play a key role in bioremediation of uranium contaminated sites.