Uranium Bioremediation Research Articles

Biostimulation of indigenous microbes for uranium bioremediation in former U mine water: multidisciplinary approach assessment

Characterizing uranium (U) mine water is necessary to understand and design an effective bioremediation strategy. In this study, water samples from two former U-mines in East Germany were analysed. The U and sulphate (SO42−) concentrations of Schlema-Alberoda mine water (U: 1 mg/L; SO42−: 335 mg/L) were 2 and 3 order of magnitude higher than those of the Pöhla sample (U: 0.01 mg/L; SO42−: 0.5 mg/L). U and SO42− seemed to influence the microbial diversity of the two water samples. Microbial diversity analysis identified U(VI)-reducing bacteria (e.g. Desulfurivibrio) and wood-degrading fungi (e.g. Cadophora) providing as electron donors for the growth of U-reducers. U-bioreduction experiments were performed to screen electron donors (glycerol, vanillic acid, and gluconic acid) for Schlema-Alberoda U-mine water bioremediation purpose. Thermodynamic speciation calculations show that under experimental conditions, U(VI) is not coordinated to the amended electron donors. Glycerol was the best-studied electron donor as it effectively removed 99% of soluble U, 95% of Fe, and 58% of SO42− from the mine water, probably by biostimulation of indigenous microbes. Vanillic acid removed 90% of U, and no U removal occurred using gluconic acid.

Bioremediation of uranium (Ⅵ) using a native strain Halomonas campaniensis ZFSY-04 isolated from uranium mining and milling effluent: Potential and mechanism

A significant surge in the exploitation of uranium resources has resulted in considerable amounts of radioactive effluents. Thus, efficient and eco-friendly uranium removal strategies need to be explored to ensure ecological safety and resource recovery. In this study, we investigated the resistance of Halomonas campaniensis strain ZFSY-04, isolated from an evaporation pool at a uranium mine site, and its potential mechanism of uranium (Ⅵ) removal. The results showed that the strain exhibited unique uranium tolerance and its growth was not significantly inhibited under a uranium concentration of 700 mg/L. It had a maximum loading capacity of 865.40 mg/g (dry weight), achieved following incubation under uranium concentration of 100 mg/L, pH 6.0, and temperature 30 °C, for 2 h, indicating that the removal of uranium by the strain was efficient and rapid. Combined with kinetic, isothermal, thermodynamic, and microspectral analyses, the mechanism of uranium loading by strain ZFSY-04 was metabolism-dependent and diverse, including, physical and chemical adsorption on the cell surface, extracellular biomineralisation, intracellular bioaccumulation, and biomineralisation. Our results highlight the unique properties of indigenous strains, including high resistance, high efficiency, rapid uranium removal, and various uranium removal strategies, which make it suitable as a new tool for in situ bioremediation and uranium-contaminated environmental resource recovery.

An experimental study for the identification of some bacterial strains for uranium bioremediation by gamma spectrometry

In this work, it was aimed to determine the potential bacterial strains that can be bioremediated of the radioactive uranium. The experimental analysis was made in gamma spectrometry. Uranyl acetate (CH3COO)2UO2.2H2O was used as the radioactive material. The radioactive solutions containing bacterial strains (P. chlororaphis (3N17-10); B. licheniformis (1N17-3); L. casei (NM-25); L. plantarum (NM-10); L. brevis (NM-26); L. lactis (NM-41); L. curvatus (NM-1); L. pentosus (NM-38); L. coryniformis (NM-22) and B. subtilis (N-28)) were prepared. A high purity germanium detector with a resolution of 490 eV at 122 keV was used to measure the photon intensities emitted from the radioactive solutions. The removal percentage and adsorbed amount of the investigated samples were determined. The results showed that P. chlororaphis have got an excellent sorption capacity for uranium removal.

The effect of not-anaerobicization and discolored bacteria on uranium reduction by Shewanella sp. RCRI7

Shewanella sp. RCRI7 is a native strain capable of reducing uranium in anaerobic conditions. In order to employ this bacterium for the bioremediation, the mutual effects of uranium and the bacteria are studied in two different approaches. The optimal settings for the bacterial proliferation capacity and uranium reduction without anaerobicization of the environment, as well as the related effects of bioremediation and bacterial color under uranium-reducing conditions, have been investigated in this study. Uranium reduction procedure was analyzed using XRD, spectrophotometry and ICP-AES. In addition, the uranium's effect on the population of the first-generation of the bacteria as well as the color and growth of the second-generation were investigated using neobar lam and CFU (Colony Forming Unit), respectively. Uranium toxicity reduced the population of non-anaerobicized bacteria more than the anaerobicized bacteria after one day of incubation, while the amount of uranium extracted by the bacteria was almost the same. In both situations, the bacteria were able to reduce uranium after two weeks of incubation. In addition to the cell counts, uranium toxicity disrupts the growth and development of healthy second-generation anaerobicized bacteria, as created creamy-colored colonies grow slower than red-colored colonies. Furthermore, due to malfunctioning cytochromes, unlike red bacteria, creamy-colored bacteria were unable to extract the optimum amount of uranium. This study reveals that reduced uranium can be produced in a deprived environment without anaerobicization. Creamy-colored Shewanella can remove soluble uranium, however the most effective bacteria have red cytochromes. These findings represent a big step forward in the industrialization of uranium bioremediation.

Bioremediation of uranium from waste effluents using novel biosorbents: a review

Bioremediation of uranium from waste effluents using novel biosorbents: a review

Unusual uranium biomineralization induced by green algae: Behavior investigation and mechanism probe

As a biosorbent, algae are frequently used for the biotreatment or bioremediation of water contaminated by heavy metal or radionuclides. However, it is unclear that whether or not the biomineralization of these metal or radionuclides can be induced by algae in the process of bioremediation and what the mechanism is. In this work, Ankistrodsemus sp. has been used to treat the uranium-contaminated water, and more than 98% of uranium in the solution can be removed by the alga, when the initial uranium concentration ranges from 10 to 80 mg/L. Especially, an unusual phenomenon of algae-induced uranium biomineralization has been found in the process of uranium bioremediation and its mineralization mechanism has been explored by multiple approaches. It is worth noticing that the biomineralization of uranium induced by Ankistrodsemus sp. is significantly affected by contact time and pH. Uranium is captured rapidly on the cell surface via complexation with the carboxylate radical, amino and amide groups of the microalgae cells, which provides nucleation sites for the precipitation of insoluble minerals. Uranium stimulates Ankistrodsemus sp. to metabolize potassium ions (K+), which may endow algae with the ability to biomineralize uranium into the rose-like compreignacite (K2[(UO2)6O4(OH)6]•8H2O). As the time increased, the amorphous gradually converted into compreignacite crystals and a large number of crystals would expand over both inside and outside the cells. To the best of our knowledge, this is the first investigated microalgae with a time-dependent uranium biomineralization ability and superior tolerance to uranium. This work validates that Ankistrodsemus sp. is a promising alga for the treatment of uranium-contaminated wastewater.

Insights on uranium removal by ion exchange columns: The deactivation mechanisms, and an overlooked biological pathway

Ion exchange (IX) is an attractive approach to extract uranium from wastewater, simultaneously reducing the negative environmental impact of uranium mining and recovering uranium resources. However, the IX process is limited by the deactivation of the resin, and the role played by microorganisms attached to the resin remains unknown. Here, we characterized the chemical and mineralogical compositions, microbial community structure, and network-related molecular mechanism of the uranium-bearing deposit on SBA exchange resin from a full-scale U mine seepage water treatment system. The uranium removal by the resin was attributed to the formation of binary anionic UO2(SO4)22− or UO2(SO4)34− complexes and their subsequent association with the resin. The deactivation of the resins might mainly result from the presence of deposits on the resin surface rather than the saturation of functional groups. Microbial reduction of U(VI) to U(IV) was confirmed in the deposit. The long-term operation acclimated functional microbial communities on the resin, such as Curvibacter sp., Acidovorax sp., and Herminiimonas sp. for uranium bioremediation, Methylotenera sp. for biofilm formation, and Polaromonas sp. and Hydrogenophaga sp. for autotrophic metabolism. Molecular ecological network analysis indicated the synthetic metabolisms among metal remediation bacteria and autotrophs might play major roles in microbial-mediated uranium removal. This study offers new insights into the application of the IX system for uranium-containing wastewater treatment.

Bioremediation of Uranium (Vi) Contaminated Groundwater Under Woodchip-Sulfur(0) Mixotrophic Condition: Decontamination Performance and Microbial Interactions

Bioremediation of Uranium (Vi) Contaminated Groundwater Under Woodchip-Sulfur(0) Mixotrophic Condition: Decontamination Performance and Microbial Interactions

Bioremediation of Uranium- and Nitrate-Contaminated Groundwater after the In Situ Leach Mining of Uranium

Uranium and nitrate are common groundwater pollutants near in situ leach uranium mines. However, we still lack techniques that can simultaneously immobilize uranium and reduce nitrate using a single bacterial species. In this study, the potential of simultaneous uranium immobilization and nitrate reduction by a single AFODN (anaerobic Fe(II) oxidizing denitrifier), Clostridium sp. PXL2, was investigated. Clostridium sp. PXL2 showed tolerance to U(VI) concentrations varying from 4.2 µM to 42 µM. The U(VI) immobilization and nitrate reduction rates in groundwater samples inoculated with this bacterium reached up to 75.1% and 55.7%, respectively, under neutral conditions. Exposure to oxidation conditions led to further U(VI) removal but did not show any noticeable effect on nitrate reduction. The U(VI) immobilization rate reached up to 85% with an increased Fe(II) initial concentration, but this inhibited nitrate reduction. SEM (scanning electron microscopy) coupled with EDS (energy dispersive spectroscopy) showed that the U(VI) immobilization was mainly due to sorption to amorphous ferric oxides. U(VI) and nitrate bioremediation by AFODNs, including Clostridium sp. PXL2, may provide a promising method for the treatment of uranium- and nitrate-contaminated groundwater after the in situ leach mining of uranium.

Application Progress of Deinococcus radiodurans in Biological Treatment of Radioactive Uranium-Containing Wastewater.

Radioactive uranium wastewater contains a large amount of radionuclide uranium and other heavy metal ions. The radioactive uranium wastewater discharged into the environment will not only pollute the natural environment, but also threat human health. Therefore, the treatment of radioactive uranium wastewater is a current research focus for many researchers. The treatment in radioactive uranium wastewater mainly includes physical, chemical and biological methods. At present, the using of biological treatment to treat uranium in radioactive uranium wastewater has been gradually shown its superiority and advantages. Deinococcus radiodurans is a famous microorganism with the most radiation resistant to ionizing radiation in the world, and can also resist various other extreme pressures. D. radiodurans can be directly used for the adsorption of uranium in radioactive waste water, and it can also transform other functional genes into D. radiodurans to construct genetically engineered bacteria, and then applied to the treatment of radioactive uranium containing wastewater. Radionuclides uranium in radioactive uranium-containing wastewater treated by D. radiodurans involves a lot of mechanisms. This article reviews currently the application of D. radiodurans that directly or construct genetically engineered bacteria in the treatment of radioactive uranium wastewater and discusses the mechanism of D. radiodurans in bioremediation of uranium. The application of constructing an engineered bacteria of D. radiodurans with powerful functions in uranium-containing wastewater is prospected.

Cupriavidus metallidurans NA4 actively forms polyhydroxybutyrate-associated uranium-phosphate precipitates

Cupriavidus metallidurans is a model bacterium to study molecular metal resistance mechanisms and its use for the bioremediation of several metals has been shown. However, its mechanisms for radionuclide resistance are unexplored. We investigated the interaction with uranium and associated cellular response to uranium for Cupriavidus metallidurans NA4. Strain NA4 actively captured 98 ± 1% of the uranium in its biomass after growing 24 h in the presence of 100 µM uranyl nitrate. TEM HAADF-EDX microscopy confirmed intracellular uranium-phosphate precipitates that were mainly associated with polyhydroxybutyrate. Furthermore, whole transcriptome sequencing indicated a complex transcriptional response with upregulation of genes encoding general stress-related proteins and several genes involved in metal resistance. More in particular, gene clusters known to be involved in copper and silver resistance were differentially expressed. This study provides further insights into bacterial interactions with and their response to uranium. Our results could be promising for uranium bioremediation purposes with the multi-metal resistant bacterium C. metallidurans NA4.

Metal removal by metallothionein and an acid phosphatase PhoN, surface-displayed on the cells of the extremophile, Deinococcus radiodurans

The utility of surface layer proteins (Hpi and SlpA) of the radiation resistant bacterium, Deinococcus radiodurans, was investigated for surface display and bioremediation of cadmium and uranium. The smtA gene, from Synechococcus elongatus (encoding the metal binding metallothionein protein), was cloned and over-expressed in D. radiodurans, either as such or as a chimeric gene fused with hpi ORF (Hpi-SmtA), or fused to the nucleotide sequence encoding the SLH domain of the SlpA protein (SLH-SmtA). The expressed fusion proteins localized to the deinococcal cell surface, while the SmtA protein localized to the cytoplasm. Recombinant cells surface-displaying the SLH-SmtA or Hpi-SmtA fusion proteins respectively removed 1.5–3 times more cadmium than those expressing only cytosolic SmtA. The deinococcal Hpi protein layer per se also contributed to U binding, by conferring substantial negative charge to deinococcal cell surface. The ORF of an acid phosphatase, PhoN was fused with the hpi or SLH domain DNA sequence and purified. Isolated Hpi-PhoN and SLH-PhoN, immobilized on deinococcal peptidoglycan showed efficient uranium precipitation (446 and 160 mg U/g biomass used respectively). The study demonstrates effective exploitation of the deinococcal S layer protein components for (a) cell surface-based sequestration of cadmium, and (b) cell-free preparations for uranium remediation.

Microbial interactions with uranium: Towards an effective bioremediation approach

In uranium bioremediation, the response of different biological groups towards uranium are critical. Understanding the metal–microbe interactions would provide adequate knowledge to develop the remediation technique. Owing to this application, many studies have been reported on various strategies using different microbial agents. These microorganisms can adsorb, accumulate, reduce, or mineralize uranium as a survival mechanism. This review is intended to discuss the plausible uranium–microbial interactions that could sequester and limit the uranium contamination in the environment. A detailed description of the key processes such as biosorption, biomineralization, bioreduction and bioaccumulation of uranium by various biological groups are provided in this review. Concise information about the uranium speciation and other environmental factors which can substantially influence the in situ bioremediation are also discussed. Finally, a comparative assessment of chemical methods versus biological procedures in the remediation of uranium was explained. This review brings out the importance of the various biological agents and factors associated with the bioremediation of uranium contaminated sites.

Resistant fungi isolated from contaminated uranium mine in Brazil shows a high capacity to uptake uranium from water

The Osamu Utsumi uranium mine occupies a 20 km2 area in the city of Caldas, which is located in the state of Minas Gerais, Brazil. Since mining activities ended at Osamu Utsumi 24 years ago, the surrounding area has become contaminated by acid effluents containing high concentrations of uranium. Thus, the aim of this study was to assess the uranium bioremediation capacity of 57 fungi isolated from the mine area. In tolerance tests, 38% (22) of the fungal isolates were considered tolerant to uranium, including 10 Penicillium species. At a uranium concentration of 2000 mg L−1 48 fungi did not exhibit mycelial growth index inhibition. Minimal inhibitory concentration (MIC) analysis showed growth of 25 fungi above a uranium concentration of 8000 mg L−1. At high uranium concentrations, some fungi (i.e., Talaromyces amestolkiae and Penicillium citrinum) showed morphological changes and pigment (melanin) production. Among the fungal isolates, those considered to be more tolerant to uranium were isolated from soil and sediment samples containing higher concentrations of heavy metal. When comparing the results of resistance/tolerance tests with those for uranium biosorption capacity, we concluded that the fungi isolated from the Osamu Utsumi mine with the best potential for uranium bioremediation were Gongronella butleri, Penicillium piscarium, Penicillium citrinum, Penicillium ludwigii, and Talaromyces amestolkiae. Biosorption tests with live fungal biomass showed that 11 species had a high potential for uranium uptake from contaminated water.

Microbial clean-up of uranium in the presence of molybdenum using pretreated Acidithiobacillus ferrooxidans

The present study is an attempt to optimize the uranium biosorption by pretreated Acidithiobacillus ferrooxidans strain ZT-94. The influences of pH, contact time, biomass dose, uranium concentration and temperature were investigated. In optimal conditions, uranium biosorption capacity was 204.44 mg/g dry weight at pH 4 during 60 min. The biosorbent was characterized by SEM microscope. The equilibrium data was fitted well by the Freundlich model with R2 = 0.8978. In the presence of molybdenum, pretreated biosorbent is tendency to adsorption of uranium. Finally, this study suggests that new biosorbent can be a potential candidate for uranium bioremediation in dual contamination with molybdenum.

Uranium bioremediation by acid phosphatase activity of Staphylococcus aureus biofilms: Can a foe turn a friend?

In this study, Staphylococcus aureus biofilms, which are considered a foe for being pathogenic, were tested for their uranium bioremediation capacity to find out if they can turn out to be a friend. Acid phosphatase activity, which is speculated to aid in bio-precipitation of U(VI) from uranyl nitrate solution, was assayed in biofilms of seven different S. aureus strains. The presence of acid phosphatase enzyme was detected in the biofilms of all S. aureus strains (in the range of 3.1 ± 0.21 to 26.90 ± 2.32 μi.u./g), and found to be higher when compared to that of their planktonic phenotypes. Among all, S. aureus V329 biofilm showed highest biofilm formation ability along with maximum phosphatase activity (26.9 ± 2.32 μi.u./g of biomass). Addition of phosphate enhanced the U(VI) remediation when treated with uranyl nitrate solution. S. aureus V329 biofilm showed significant U tolerance with only a 3-log reduction when exposed to 10 ppm U(VI) for 1 h. When treated in batch mode, V329 biofilm successfully remediated up to 47% of the 10 ppm U(VI). This new approach using the acid phosphatase from the S. aureus V329 biofilm presents an alternative method for the remediation of uranium contamination.

Characterization of arsenic oxidation and uranium bioremediation potential of arsenic resistant bacteria isolated from uranium ore.

Arsenic (As) is often found naturally as the co-contaminant in the uranium (U)-contaminated area, obstructing the bioremediation process. Although the U-contaminated environment harbors microorganisms capable of interacting with U which could be exploited in bioremediation. However, they might be unable to perform with their full potential due to As toxicity. Therefore, potential in arsenic resistance and oxidation is greatly desired among the microorganisms for a continued bioremediation process. In this study, arsenic-resistant bacteria were isolated from U ore collected from Bundugurang U mine, characterized and their As oxidation and U removal potentials were determined. 16S rRNA gene sequencing and phylogenetic analysis showed the affiliation of isolated bacteria with Microbacterium, Micrococcus, Shinella, and Bacillus. Except Bacillus sp. EIKU7, Microbacterium sp. EIKU5, Shinella sp. EIKU6, and Micrococcus sp. EIKU8 were found to resist more than 400mM As(V); however, all the isolates could survive in 8mM As(III). The isolates were found to readily oxidize As under different culture conditions and are also resistant towards Cd, Cr, Co, Ni, and Zn. All the isolates could remove more than 350mgU/g dry cells within 48h which were found to be highly dependent upon the concentration of U, biomass added initially, and on the time of exposure. Ability of the isolates to grow in nitrogen-free medium indicated that they can flourish in the nutrition deprived environment. Therefore, the recovery of isolates with the potent ability to resist and oxidize As from U ore might play an important role in toxic metal bioremediation including U.

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.

Uranium (VI) bioremediation by Acinetobacter sp. USCB2 isolated from uranium tailings area

Bioremediation of uranium (VI)-contaminated aquifers was investigated by using bacteria isolated from a uranium tailing in South China. The bacteria were identified as Acinetobacter on the basis of physiological, biochemical tests and 16S rDNA sequence homology analysis. The protein concentration in the supernatant declined from 50.26 μ g/mL to 40.01 μ g/mL after uranium removal, and the activity of bacterial phosphatase increased from 36.04 U/L to 39.81 U/L. The FTIR, SEM-EDS and XRD demonstrated the involvement of functional groups in U (VI) binding, U accumulated on the surface of the bacteria and the precipitated is Uranyl Sulfite Hydrate. The results from this study demonstrate the potential of the U tolerant, bacterium Acinetobacter sp. USC B2 isolate might be considered as promising candidates in the design of uranium bioremediation strategies.

Kinetics and pH-dependent uranium bioprecipitation by Shewanella putrefaciens under aerobic conditions

The removal behavior of U(VI) by Shewanella putrefaciens was investigated in this study. Our results demonstrated the formation of uranium phosphate biomineral, predominantly existed as chernikovite [H2(UO2)2(PO4)2·8H2O], on the cell surface of S. putrefaciens. The lamellar chernikovite was found at slightly acid pH, but not at pH > 7.0. Phosphate-containing groups played the key role in the formation of chernikovite based on the analysis of IR. After ashing and hydrothermal process, bacterially mediated chernikovite can be transformed into inorganic uranium phosphate and UO2, respectively. The findings can provide a potential strategy for in situ bioremediation of uranium in aerobic environment. Biomineralization process of uranium on S. putrefaciens.