Biomineralization mechanism of U(VI) induced by Bacillus cereus 12-2: The role of functional groups and enzymes

Efficient uranium sequestration ability and mechanism of live and inactivated strain of Streptomyces sp. HX-1 isolated from uranium wastewater

Prokaryotes are effective biosorbents for the recovery of uranium and other heavy metals. However, the potential mechanism of uranium bioaccumulation by filamentous strain (actinobacteria) remains unclear. This study demonstrates the potential for and mechanism of uranium bioaccumulation by living (L-SS) and inactivated (I-SS) Streptomyces sp. HX-1 isolated from uranium mine waste streams. Uranium accumulation experiments showed that L-SS and I-SS had efficient uranium adsorption potentials, with removal rates of 92.93 and 97.42%, respectively. Kinetic and equilibrium data indicated that the bioaccumulation process was consistent with the pseudo-second-order kinetic, Langmuir, and Sips isotherm models. FTIR indicated that the main functional groups of L-SS and I-SS binding uranium were uranyl, carboxyl, and phosphate groups. Moreover, the results of XRD, XPS, SEM-EDS, and TEM-EDS analyses revealed for the first time that L-SS has biomineralization and bioreduction capacity against uranium. L-SS mineralize U(VI) into NH4UO2PO4 and [Formula: see text] through the metabolic activity of biological enzymes (phosphatases). In summary, Streptomyces sp. HX-1 is a novel and efficient uranium-fixing biosorbent for the treatment of uranium-contaminated wastewater.

Anodic Electrodepositing Bioinspired Cu-BDC-NH2@Graphene Oxide Membrane for Efficient Uranium Extraction

The challenge of removing trace levels of heavy metal ions, particularly uranium, from wastewater is a critical concern in environmental management. Uranium, a key element in long-term nuclear power generation, often poses significant extraction difficulties in wastewater due to its low concentration, interference from other ions, and the complexity of aquatic ecosystems. This study introduces an anodic electrodeposited hierarchical porous 2D metal-organic framework (MOF) Cu-BDC-NH2@graphene oxide (GO) membrane for effective uranium extraction by mimicking the function of the superb-uranyl-binding protein. This membrane is characterized by its hierarchical pillared-layer structures resulting from the controlled orientation of Cu-BDC-NH2 MOFs within the laminated GO layers during the electrodeposition process. The integration of amino groups from 2D Cu-BDC-NH2 and carboxylate groups from GO enables a high affinity to uranyl ions, achieving an unprecedented uranium adsorption capacity of 1078.4 mg/g and outstanding selectivity. Our findings not only demonstrate a breakthrough in uranium extraction technology but also pave the way for advancements in water purification and sustainable energy development, proposing a practical and efficient strategy for creating orientation-tunable 2D MOFs@GO membranes tailored for high-efficiency uranium extraction.

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.

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.

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.

Impact of microbial processes on the safety of deep geological repositories for radioactive waste

To date, the increasing production of radioactive waste due to the extensive use of nuclear power is becoming a global environmental concern for society. For this reason, many countries have been considering the use of deep geological repositories (DGRs) for the safe disposal of this waste in the near future. Several DGR designs have been chemically, physically, and geologically well characterized. However, less is known about the influence of microbial processes for the safety of these disposal systems. The existence of microorganisms in many materials selected for their use as barriers for DGRs, including clay, cementitious materials, or crystalline rocks (e.g., granites), has previously been reported. The role that microbial processes could play in the metal corrosion of canisters containing radioactive waste, the transformation of clay minerals, gas production, and the mobility of the radionuclides characteristic of such residues is well known. Among the radionuclides present in radioactive waste, selenium (Se), uranium (U), and curium (Cm) are of great interest. Se and Cm are common components of the spent nuclear fuel residues, mainly as 79Se isotope (half-life 3.27 × 105 years), 247Cm (half-life: 1.6 × 107 years) and 248Cm (half-life: 3.5 × 106 years) isotopes, respectively. This review presents an up-to-date overview about how microbes occurring in the surroundings of a DGR may influence their safety, with a particular focus on the radionuclide-microbial interactions. Consequently, this paper will provide an exhaustive understanding about the influence of microorganisms in the safety of planned radioactive waste repositories, which in turn might improve their implementation and efficiency.

Mechanism of lead adsorption by a Bacillus cereus strain with indole-3-acetic acid secretion and inorganic phosphorus dissolution functions

BACKGROUND

Heavy metal pollution has become a major source of environmental pollution because of increasing industrialization. Microbial remediation is a promising approach to remediate lead-contaminated environments owing to its cost-effective, environment-friendly, ecologically sustainable, and highly efficient properties. In this study, the growth-promoting functions and lead-adsorption ability of Bacillus cereus SEM-15 were examined, and the functional mechanism of the strain was preliminarily identified using scanning electron microscopy, energy spectrum, infrared spectrum, and genome analyses, providing theoretical support for utilization of B. cereus SEM-15 in heavy metals remediation.

RESULTS

B. cereus SEM-15 showed strong ability to dissolve inorganic phosphorus and secrete indole-3-acetic acid. The lead adsorption efficiency of the strain at lead ion concentration of 150 mg/L was more than 93%. Single factor analysis revealed the optimal conditions for heavy metal adsorption by B. cereus SEM-15 (adsorption time, initial lead ion concentration, pH, and inoculum amount were 10 min, 50-150 mg/L, 6-7, and 5 g/L, respectively) in nutrient-free environment, with the lead adsorption rate reaching 96.58%. Scanning electron microscopy of B. cereus SEM-15 cells before and after lead adsorption showed adherence of a large number of granular precipitates to the cell surface after lead adsorption. X-Ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results indicated the characteristic peaks of Pb-O, Pb-O-R (R = functional group), and Pb-S bonds after lead adsorption, and a shift in the characteristic peaks of bonds and groups related to C, N, and O. Genome annotation results showed the presence of genes related to heavy metals tolerance and plant growth promotion in B. cereus SEM-15, providing a molecular basis for the strain's heavy metals tolerance and plant growth promotion functions.

CONCLUSIONS

This study analyzed the lead adsorption characteristics of B. cereus SEM-15 and the associated influencing factors, and discussed the adsorption mechanism and related functional genes, providing a basis for clarifying the underlying molecular mechanism and offering a reference for further research on plant-microorganisms combined remediation of heavy metals polluted environments.

The remediation of uranium-contaminated groundwater via bioreduction coupled to biomineralization with different pH and electron donors

Stimulating indigenous microbes to reduce aqueous U(VI) to insoluble U(IV) by adding an electron donor has been applied as an applicable strategy to remediate uranium-contaminated groundwater in situ. However, biogenic U(IV) minerals are susceptible to oxidative remobilization after exposure to oxygen. To enhance the stability of the end product, glycerol phosphate (GP) was selected to treat artificial uranium-containing groundwater at different pH values (i.e., 7.0 and 5.0) with glycerol (GY) as the control group. The results revealed that removal ratios of uranium with GP were all higher than those with GY, and reduced crystalline U(IV)-phosphate and U(VI)-phosphate minerals (recalcitrant to oxidative remobilization) were generated in the GP groups. Although bioreduction efficiency was influenced at pH 5.0, the stability of the end product with GP was elevated significantly compared with that with GY. Mechanism analysis demonstrated that GP could activate bioreduction and biomineralization of the microbial community, and two stages were included in the GP groups. In the early stage, bioreduction and biomineralization were both involved in the immobilization process. Subsequently, part of the U(VI) precipitate was gradually reduced to U(IV) precipitate by microorganisms. This work implied that the formation of U-phosphate minerals via bioreduction coupled with biomineralization potentially offers a more effective strategy for remediating uranium-contaminated groundwater with long-term stability.

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.

Effect of different phosphate sources on uranium biomineralization by the Microbacterium sp. Be9 strain: A multidisciplinary approach study

Introduction

Industrial activities related with the uranium industry are known to generate hazardous waste which must be managed adequately. Amongst the remediation activities available, eco-friendly strategies based on microbial activity have been investigated in depth in the last decades and biomineralization-based methods, mediated by microbial enzymes (e.g., phosphatase), have been proposed as a promising approach. However, the presence of different forms of phosphates in these environments plays a complicated role which must be thoroughly unraveled to optimize results when applying this remediation process.

Methods

In this study, we have looked at the effect of different phosphate sources on the uranium (U) biomineralization process mediated by Microbacterium sp. Be9, a bacterial strain previously isolated from U mill tailings. We applied a multidisciplinary approach (cell surface characterization, phosphatase activity, inorganic phosphate release, cell viability, microscopy, etc.).

Results and Discussion

It was clear that the U removal ability and related U interaction mechanisms by the strain depend on the type of phosphate substrate. In the absence of exogenous phosphate substrate, the cells interact with U through U phosphate biomineralization with a 98% removal of U within the first 48 h. However, the U solubilization process was the main U interaction mechanism of the cells in the presence of inorganic phosphate, demonstrating the phosphate solubilizing potential of the strain. These findings show the biotechnological use of this strain in the bioremediation of U as a function of phosphate substrate: U biomineralization (in a phosphate free system) and indirectly through the solubilization of orthophosphate from phosphate (P) containing waste products needed for U precipitation.

Effect of the phosphate solubilization and mineralization synergistic mechanism of Ochrobactrum sp. on the remediation of lead

Phosphate-solubilizing bacteria (PSB) promotes the formation of mineralized precipitation through phosphorous dissolution and mineralization, forming stable lead (Pb(II)) minerals and reducing the migration of Pb(II) in the environment. In this study, a Pb-tolerant strain Ochrobactrum sp. J023 from a contaminated soil around a battery factory in Jiangsu Province, China, was screened for experiments to investigate the phosphate solubilization and mineralization mechanism of this strain. The organic acids and the acid phosphatase produced by the bacteria have a synergistic effect on phosphate dissolution. When the pH of the culture medium decreased to the lowest 4.55, the amount of soluble phosphate and the activity of acid phosphatase reached the maximum 161.29 mg L^-1 and 61.98 U mL^-1, and there was a significant correlation between the concentration of soluble phosphate and the activity of acid phosphatase (R = 0.832**, P < 0.05). It was found that acetic acid played the most important role in the secreted organic acids. During the mineralization reaction, the extracellular polymeric substances (EPS) chelates part of the Pb(II) on the surface of the cell wall, preventing the metal Pb from penetrating into the cell, thus providing protection to the strain. Meanwhile, due to the nucleation sites provided by cell surface groups (carboxyl and phosphate groups), a large number of metal ions are absorbed to promote the formation of crystallization. The final mineralized product of Pb(II) by strain J023 was pyroxite (Pb₅(PO₄)₃X, where X = Cl, OH). The mechanism of phosphate dissolution and mineralization proposed by us is that the organic acids and acid phosphatases secreted by phosphate-solubilizing bacteria promote the increase of PO₄^3- concentration in the solution, the complexation of metal cations and cell surface groups will induce the formation of mineralized precipitation under the catalysis of enzyme. Therefore, it is a promising strategy for bioremediation of lead pollution by screening functional strains with strong abilities of phosphate solubility and mineralization.

Surface biomineralization of uranium onto Shewanella putrefaciens with or without extracellular polymeric substances

The influence of extracellular polymeric substances (EPS) on the interaction between uranium [U(VI)] and Shewanella putrefaciens (S. putrefaciens), especially the U(VI) biomineralization process occurring on whole cells and cell components of S. putrefaciens was investigated in this study. The removal efficiency of U(VI) by S. putrefaciens was decreased by 22% after extraction of EPS. Proteins were identified as the main components of EPS by EEM analysis and were determined to play a major role in the biosorption of uranium. SEM-EDS results showed that U(VI) was distributed around the whole cell as 500-nanometer schistose structures, which consisted primarily of U and P. However, similar uranium lamellar crystal were wrapped only on the surface of EPS-free S. putrefaciens cells. FTIR and XPS analysis indicated that phosphorus- and nitrogen-containing groups played important roles in complexing U (VI). XRD and U L_III-edge EXAFS analyses demonstrated that the schistose structure consisted of hydrogen uranyl phosphate [H₂(UO₂)₂(PO₄)₂•8H₂O]. Our study provides new insight into the mechanisms of induced uranium crystallization by EPS and cell wall membranes of living bacterial cells under aerobic conditions.

The dynamic behavior and mechanism of uranium (VI) biomineralization in Enterobacter sp. X57

The important role of microbes in the biomineralization and migration behavior of uranium in the field of environmental chemistry has been well emphasized in previous work. However, limited work on mineralization processes of indigenous microorganism has prevented us from a deeper understanding of the process and mechanisms of uranium biomineralization. In this work, the dynamic process and mechanism of uranium biomineralization in Enterobacter sp. X57, a novel uranium-tolerant microorganism separated from uranium contaminated soil, were systematically investigated. Enterobacter sp. X57 can induce intracellular mineralization of U (VI) to Uramphite (NH₄UO₂PO₄·3H₂O) under neutral conditions by alkaline phosphatase. In this biomineralization process, soluble U (VI) first bonded with the amino and phosphate groups on the plasma membrane, providing initial nucleation site for the formation of U (VI) biominerals. Then the impairment of cell barrier function and the enhancement of alkaline phosphatase metabolism occurred with the accumulation of uranium in cells, creating a possible pathway for soluble U (VI) to diffuse into the cell and be further mineralized into U (VI)-phosphate minerals. All the results revealed that the intracellular biomineralization of uranium by Enterobacter sp. X57 was a combined result of biosorption, intracellular accumulation and phosphatase metabolism. These findings may contribute to a better understanding of uranium biomineralization behavior and mechanism of microorganisms, as well as possible in-situ bioremediation strategies for uranium by indigenous microorganisms.

Continuous and efficient immobilization of heavy metals by phosphate-mineralized bacterial consortium

Traditional sewage treatment technology cannot remove heavy metals, which needs to be improved urgently. Lysinibacillus with the function of bio-mineralization was screened and loaded on granular sludge to form a phosphate-mineralized bacterial consortium, which demonstrated the ability of self-regulating pH and automatic solid-liquid separation. Heavy metals could be fixed on the bacterial consortium to produce stable and harmless phosphate minerals. The highest removal efficiency of Pb(Ⅱ), Cd(Ⅱ), and Ni(Ⅱ) were 97.9%, 70%, and 40%, respectively. Organic matter and other metal ions in actual polluted water had little effect on the Pb(Ⅱ) removal efficiency. Mechanism analysis was conducted through 3D-EEM, XRD, SEM-EDS, XPS, FTIR, and high-throughput sequencing analyses. The bacterial consortium was a multi-species coexistence system, but Lysinibacillus played a major role in removing Pb(Ⅱ). C-O and O-H bonds of tyrosine and phosphorous organics were broken by enzyme catalysis and the metal-oxygen bond (Pb-O) was formed. Mineral crystals in the reactor accumulated, transforming from the initial phase non-crystalline structure to the metaphase Pb₃(PO₄)₂ and eventually to the Pb₅(PO₄)₃OH. This research obtained a promising technique for immobilizing Pb(Ⅱ) or other hazardous metals continuously and efficiently.

Uranium sequestration abilities of Bacillus bacterium isolated from an alkaline mining region

The present study elaborates uranium sequestration by bacteria from alkaline wastewaters. In the investigation, a few bacterial strains were isolated from alkaline uranium mine water and were tested for uranium sequestration properties 16S rRNA analysis assigned the 10 bacterial isolates to 4 genera of Actinobacteria and Firmicutes. Among all the isolates tested, the strain Bacillus aryabhattai (TP03) has shown superior sequestration capacity at 5 and 10 mg/L U in 1 mM carbonate-bicarbonate buffer at pH 9.2. At low uranium concentrations (5 mg/L as uranyl carbonate), the strain could sequester ~70% of the uranium in 6 h with a loading capacity of 4.3 mg U/g dry bacterial biomass. Increase in carbonate-bicarbonate buffer concentrations and pH reduced the sequestration capacity. Scanning electron microscopy and energy dispersive X-ray fluorescence spectroscopy studies indicated the presence of uranium with the bacterial biomass. Fourier transform infra-red spectroscopy results confirmed the uranium sequestration by cell membrane phosphate, amide, and carboxyl functional groups. Transmission electron microscopy study showed uranium presence within the cell cytoplasm, thus supporting the hypothesis on active metabolism-dependent bioaccumulation of uranium. The kinetics study of uranium sequestration was well fitted to the pseudo-second-order model. Overall, this study infers that the isolated alkaliphilic bacteria from the mine waters have significant sequestration property for treating uranium-containing alkaline wastewaters.

Microbial interaction with and tolerance of radionuclides: underlying mechanisms and biotechnological applications

Radionuclides (RNs) generated by nuclear and civil industries are released in natural ecosystems and may have a hazardous impact on human health and the environment. RN-polluted environments harbour different microbial species that become highly tolerant of these elements through mechanisms including biosorption, biotransformation, biomineralization and intracellular accumulation. Such microbial-RN interaction processes hold biotechnological potential for the design of bioremediation strategies to deal with several contamination problems. This paper, with its multidisciplinary approach, provides a state-of-the-art review of most research endeavours aimed to elucidate how microbes deal with radionuclides and how they tolerate ionizing radiations. In addition, the most recent findings related to new biotechnological applications of microbes in the bioremediation of radionuclides and in the long-term disposal of nuclear wastes are described and discussed.

Lab-scale evaluation of the microbial bioremediation of Cr(VI): contributions of biosorption, bioreduction, and biomineralization

Bioremediation of Cr(VI) by microorganisms has attracted immense research interests. There are three different mechanisms for bioremediation of Cr(VI): biosorption, bioreduction, and biomineralization. Identifying the relative contributions of these different mechanisms to Cr(VI) bioremediation can provide valuable information to enhance the final result. This article explores the corresponding contributions of different mechanisms in the Cr(VI) bioremediation process. To obtain a deeper understanding of each bioremediation mechanism, the corresponding precipitation products were analyzed via different methods. Fourier transform infrared spectrometer (FTIR) analysis showed that Cr(VI) was adsorbed by functional groups in EPS to form a chelate compound. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis determined that the stable Cr(III) compounds and mineral crystals which contain chromium gradually formed during the bioremediation process. High-throughput sequencing technology was applied to monitor microbial community succession. The results showed that the total removal rate of Cr(VI) reached 77.64% in 56 days in 100 mg/L Cr(VI). Bioreduction was the major contributor to the final result, followed by biosorption and biomineralization; their proportions are 69.61%, 19.16%, and 11.23%, respectively. Besides, the high-throughput sequencing data indicated that reductive microorganisms were the dominant flora and that the relative abundance of different reductive microorganism types changes significantly. This work has clarified the contributions of different mechanisms during Cr(VI) bioremediation process and provided a new enhancement strategy for Cr(VI) bioremediation.Graphical abstract.

Reducing cadmium bioavailability and accumulation in vegetable by an alkalizing bacterial strain

Cadmium (Cd) contamination in agricultural soils is a widespread environmental problem that can affect food safety and human health. Effective remediation methods are needed to reduce Cd bioavailability in soil and Cd accumulation in food crops. In the present study, we isolated a Cd-resistant and alkalizing bacterium strain XT-4 from a Cd-contaminated soil and evaluated its potential application in Cd bioremediation. Based on its morphological, physiological and biochemical characteristics, together with 16S rRNA gene sequence analysis, strain XT-4 was identified as a member of the Bacillus genus. Strain XT-4 showed a strong ability to increase the pH and decrease Cd solubility in the medium. A greenhouse-based pot experiment with a Cd-contaminated soil was conducted to evaluate the effect of strain XT-4 inoculation on the growth and Cd accumulation of the vegetable Pak choi (Brassica rapa ssp. chinensis). Inoculation increased the rhizosphere pH, decreased CaCl₂-extractable Cd in the soil and decreased Cd concentration in the edible part of Pak choi by 28-40%. The results suggest that inoculation with alkalizing bacterial strain XT-4 represents an effective solution to increase rhizosphere pH and decrease Cd uptake by vegetable crops in Cd-contaminated acid soils.

Multisystem combined uranium resistance mechanisms and bioremediation potential of Stenotrophomonas bentonitica BII-R7: Transcriptomics and microscopic study

The potential use of microorganisms in the bioremediation of U pollution has been extensively described. However, a lack of knowledge on molecular resistance mechanisms has become a challenge for the use of these technologies. We reported on the transcriptomic and microscopic response of Stenotrophomonas bentonitica BII-R7 exposed to 100 and 250 μM of U. Results showed that exposure to 100 μM displayed up-regulation of 185 and 148 genes during the lag and exponential phases, respectively, whereas 143 and 194 were down-regulated, out of 3786 genes (>1.5-fold change). Exposure to 250 μM of U showed up-regulation of 68 genes and down-regulation of 290 during the lag phase. Genes involved in cell wall and membrane protein synthesis, efflux systems and phosphatases were up-regulated under all conditions tested. Microscopic observations evidenced the formation of U-phosphate minerals at membrane and extracellular levels. Thus, a biphasic process is likely to occur: the increased cell wall would promote the biosorption of U to the cell surface and its precipitation as U-phosphate minerals enhanced by phosphatases. Transport systems would prevent U accumulation in the cytoplasm. These findings contribute to an understanding of how microbes cope with U toxicity, thus allowing for the development of efficient bioremediation strategies.

The importance of the bacterial cell wall in uranium(VI) biosorption

The bacterial cell envelope, in particular the cell wall, is considered the main controlling factor in the biosorption of aqueous uranium(vi) by microorganisms. However, the specific roles of the cell wall, associated biomolecules, and other components of the cell envelope are not well defined. Here we report findings on the biosorption of uranium by isolated cell envelope components and associated biomolecules, with P. putida 33015 and B. subtilis 168 investigated as representative strains for the differences in Gram-negative and Gram-positive cell envelope architecture, respectively. The cell wall and cell surface membrane were isolated from intact cells and characterised by X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FT-IR) spectroscopy; revealing variations in the abundance of functional moieties and biomolecules associated with components of the cell envelope. Uranium biosorption was investigated as a function of cell envelope component and pH, comparing with intact cells. The isolated cell wall from both strains exhibited the greatest uranium biosorption capacity. Deprotonation of favourable functional groups on the biomass as the pH increased from 3 to 5.5 increased their uranium biosorption capacity by approximately 3 fold. The results from ATR-FT-IR indicated that uranium(vi) biosorption was mediated by phosphate and carboxyl groups associated with proteins and phosphorylated biopolymers of the cell envelope. This includes outer membrane phospholipids and LPS of Gram-negative bacteria and teichoic acids, surface proteins and peptidoglycan from Gram-positive bacteria. As a result, the biosorption process of uranium(vi) to microorganisms is controlled by surface interactions, resulting in higher accumulation of uranium in the cell envelope. This demonstrates the importance of bacterial cell wall as the key mediator of uranium biosorption with microorganisms.

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.

Fabrication and Optimization of the Thermo-Sensitive Hydrogel Carboxymethyl Cellulose/Poly(N-isopropylacrylamide-co-acrylic acid) for U(VI) Removal from Aqueous Solution

In this work, the thermo-sensitive materials N-isopropylacrylamide (NIPAM) and acrylic acid (AA) were crosslinked with carboxymethyl cellulose (CMC) (CMC/P (NIPAM-co-AA)) via a free radical polymerization method for the removal of U(VI) from aqueous solution. The L16 (45) orthogonal experiments were designed for the optimization of the synthesis condition. The chemical structures of the crosslinking hydrogel were confirmed by FTIR spectroscopy. The microstructural analyses were conducted though scanning electron microscopy (SEM) to show the pore structure of the hydrogel. The adsorption performance of the CMC/P (NIPAM-co-AA) hydrogel for the uptake of U(VI) from simulated wastewater was also investigated. The adsorption reached equilibrium within 1 h. Under the reaction of pH = 6 and a temperature of 298 K, an initial concentration of U(VI) of 5 mg·L-1, and 10 mg of the CMC/P(NIPAM-co-AA) hydrogel, the maximum adsorption capacity was 14.69 mg g-1. The kinetics fitted perfectly with the pseudo-second-order model, and the isotherms for the composite hydrogel adsorption of U(VI) was in accordance with the Langmuir model. The chemical modification confirmed that the acylamino group played an important role in uranium adsorption. The desorption and reusability study revealed that the resolution rate was still available at approximately 77.74% after five alternate heating cycles at 20 and 50 °C of adsorption-desorption.

Cupriavidus sp. strain Cd02-mediated pH increase favoring bioprecipitation of Cd2+ in medium and reduction of cadmium bioavailability in paddy soil

This study investigated the effects of Cupriavidus sp. strain Cd02-mediated increase on biosorption and bioprecipitation of Cd²⁺ during the 144-h cultivation time as well as evaluated effectivenesses of changing soil pH and bioavailability of cadmium after bioaugmentation of strain Cd02 into Cd-contaminated paddy soil for 15 days. Results showed that strain Cd02-induced pH increase of the culture medium (from 7.40 to 8.68) facilitated biosorption of Cd²⁺ on Cd02 cell surface (4.82 mg/mg) and extracellular bioprecipitation in form of cadmium carbonate (3.07 mg/mg). Also, the pH values of Cd-contaminated paddy soil increased by 1.41 units after strain Cd02 was applied for 15 days, which thereby promoted the decrease of exchangeable fraction of Cd²⁺ by 6.5% in the tested paddy soil. Meanwhile, strain Cd02 could prosperously live in paddy soils after bioaugmentation. These results suggest that strain Cd02 may be applicable for bioremediation of the heavy metal-contaminated soils by bioaugmentation.

Nonreductive biomineralization of uranium by Bacillus subtilis ATCC-6633 under aerobic conditions

Nonreductive biomineralization of uranium is a promising methodology for the removal of uranium contamination as it provides stable products and wide applications. However, the efficiency of mineralization has become a major obstacle for the removal of uranium contamination by this technology, and the mineralizing process still remains largely obscure. To solve this problem in a practical way, we report a fast nonreductive biomineralization process of uranium by Bacillus subtilis ATCC-6633, a widespread bacterium with environmentally-friendly applications. In this system, we demonstrated that the size and crystallization degree of the obtained nonreduced biomineralized products is significantly superior to the results reported in the literature under comparable conditions. Meanwhile, combined with SEM, TEM, and FT-IR, a mineralization process of uranium transfer from the outer surface of the Bacillus subtilis ATCC-6633 to the internal has been clearly observed, which was accompanied by the evolution of amorphous U(VI) to crystalline uramphite. This work uncovers whole-process insights into the nonreductive biomineralization of uranium by Bacillus subtilis ATCC-6633, paving a new way for the rapid and sustained removal of uranium contamination.

Ultrafast Recovery of Uranium from Seawater by Bacillus velezensis Strain UUS-1 with Innate Anti-Biofouling Activity

Highly-efficient recovery of uranium from seawater is of great concern in the growing demand for nuclear energy. Bacteria are thought to be potential alternatives for uranium recovery. Herein, a Bacillus velezensis strain, UUS-1, with highly-efficient uranium immobilization capacity is isolated and is used in the recovery of uranium from seawater. The strain exhibits time-dependent uranium recovery capacity and only immobilizes uranium after growing for 12 h. The carboxyl group together with the amino group inside the bacterial cells, but not previously identified phosphate group, are essential for uranium immobilization. UUS-1 shows broad-spectrum antimicrobial activity by producing diverse antimicrobial metabolites, which endows the strain with innate resistance to the biofouling of marine microorganisms. Based on the dry weight of the initially used bacterial cultures, UUS-1 concentrates uranium by 6.26 × 105 times and reaches the high immobilization capacity of 9.46 ± 0.39 mg U g-1 bacterial cultures in real seawater within 48 h, which is the fastest uranium immobilization capacity observed from real seawater. Overall considering the ultrafast and highly-efficient uranium recovery capacity and the innate anti-biofouling activity, UUS-1 is a promising alternative for uranium recovery from seawater.

Effective UO22+ removal from aqueous solutions using lichen biomass as a natural and low-cost biosorbent

The UO₂²⁺ biosorption properties of a lichen, Evernia prunastri, from aqueous solutions were investigated. The widely occurring lichen samples were collected from the forest in Bilecik-Turkey. The UO₂²⁺ biosorption onto lichen was characterized by FT-IR and SEM-EDX analysis techniques before and after biosorption. The effects of the solution pH, biosorbent dosage, UO₂²⁺ concentration, contact time, and temperature on UO₂²⁺ biosorption on lichen sample were studied by using the batch method. The isotherm experimental data were described using isotherm models of Langmuir, Freundlich and Dubinin Radushkevich. The maximum UO₂²⁺ biosorption capacity of the lichen sample was estimated by the Langmuir equation to be 0.270 mol kg^-1. The adsorption energy from the Dubin Radushkevich model was found to be 8.24 kJ mol^-1. Kinetic data determined that the biosorption was best described by the pseudo-second-order kinetic model. Thermodynamic findings showed that the biosorption process was endothermic, entropy increased and spontaneous. In conclusion, the lichen appears to be a promising biosorbent for the removal of UO₂²⁺ ions from aqueous solutions because of high biosorption capacity, easy usability, low cost, and high reusability performance.

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.