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

Potential risks of in-situ microbial remediation of uranium-contaminated groundwater: Uranium release and remigration

After in-situ microbial remediation of uranium-contaminated groundwater, the environmental problems caused by the remigration of uranium immobilized in the aquifer due to microbial decay require attention. In this study, uranium-containing Leifsonia sp. spoilage was produced by natural decay of uranium-adsorbed Leifsonia sp.. Batch experiments were used to investigate the influence on uranium release from the Leifsonia sp. spoilage under the conditions of different pH, action time, and concentrations of the metal ions K+, Ca2+, Na+, Mg2+, and Zn2+. The remigration of immobilized uranium was simulated by the Leifsonia sp. spoilage sand column experiment. The release rate of uranium initially decreased with increasing pH, increased with increasing contact time, and then remained unchanged with increasing time; the release rate of uranium peaked at 4.98 % at pH 3 and 120 h. Compared to the absence of metal ions, the release rate of uranium increased by >10 % under the action of metal ions, in which Ca2+had the greatest effect, up to 18.4 %. Furthermore, U(IV) in the spoilage was oxidized to U(VI), resulting in uranium release, and uranium release was related to hydroxyl, carboxyl, amino, and amide groups in the spoilage. The release kinetics of uranium were consistent with those of the Elovich and double constant models, indicating that the release of uranium was a multifactorial integrated chemical desorption process. In addition, the remigrated uranium in groundwater had two components: some of the uranium was released from the spoilage and migrated independently as uranyl ions, and some was present in the spoilage and migrated with the spoilage, the amount of the former being much greater than that of the latter. This study provides a theoretical basis for the rational use of microbial in-situ remediation of uranium-contaminated groundwater by in-situ leaching of uranium.

Methylobacterium sp. EIKU22 as a strategic bioinoculant for uranium and arsenic mitigation in agricultural soil: a microbial solution for sustainable agriculture

Mitigation of potentially toxic elements (PTEs) such as uranium (U) and arsenic (As), and fulfilment of global food demand requires a sustainable approach. Therefore, a multiple PTE-tolerant Methylobacterium sp. EIKU22 was explored for its bioremediation and biofertilization potential. This multi-metal tolerant isolate removed 29.88% U (initial dose: 100 mg L-1, pH 4.0, biosorption 3.74 mg g-1) after 14 days, following pseudo-second-order (PSO) kinetics. The isolate also showed 54% As(III) [pseudo-first-order kinetic; 3.72 mg g-1]; and ~ 37% As(V) (PSO; 2.4 mg g-1) removal within 60 min with the same initial dosing of either As(III) or As(V). Moreover, the strain precipitated > 96.5% and ~ 97% of U using released phosphate from inorganic and organic sources, respectively. Further analysis with inorganic phosphate showed > 31%, > 41% and > 98% of U precipitation from initial doses of 1000, 500 and 100 mg L-1 within 5 min. Methylobacterium sp. EIKU22 expresses the potential to solubilize ~ 178% phosphate, 169.8% potassium, 156-213% zinc within 6 days, and was able to withstand a pH range of 4.0-8.0, temperature range of 20-35 °C, and exhibited resilience to up to 10% NaCl exposure despite being affected by UV exposure. Further, the isolate showed to grow in nitrogen-free media and produce IAA, ammonia, siderophore, ACC deaminase, cellulase and catalase, suggesting potential application in plant growth promotion. The isolate harbours amoA, and nifH genes and imparts better survivability and vegetative growth in the rice seedling. These findings showcase the strain's dual applicability. However, further investigation is needed to generalize the findings.

Radiation tolerance and biodegradation performance of a marine bacterium Acinetobacter sp. Y9 in radioactive composite oil-contaminated wastewater

The tolerance and degradation characteristics of a marine oil-degrading strain Acinetobacter sp. Y9 were investigated in the presence of diesel oil and simulated radioactive nuclides (Mn2+, Co2+, Ni2+, Sr2+, Cs+) at varying concentrations, as well as exposure to γ-ray radiation (Co-60). The maximum tolerable concentrations for Co2+and Ni2+ were found to be 5 mg/l and 25 mg/l, respectively, while the tolerable concentrations for Mn2+, Sr2+, and Cs+ exceeded 400 mg/l, 1000 mg/l, and 1000 mg/l, respectively. A total of 0.4 Gy/h of γ-ray radiation (Co-60) did not significantly affect the growth of strain Y9. The presence of metal nuclides and γ-ray radiation primarily inhibited the production of outer membrane proteins while promoting the secretion of polysaccharides in strain Y9. Strain Y9 exhibited a notable capacity to degrade diesel oil under radiative conditions when exposed to the five individual radionuclides used in this study. Furthermore, the introduction of the radiation-resistant strain R1 significantly enhanced the diesel oil degradation efficiency of strain Y9 in the presence of a mixture of five nuclides, with the degradation efficiency increasing from 26.7% to 46.75%. Strain R1 demonstrated the ability to absorb a substantial amount of free nuclides, thereby creating favorable environmental conditions for the growth and degradation activity of strain Y9. PRACTITIONER POINTS: Investigate the tolerance mechanisms of strain Y9 to different nuclides and γ-ray irradiation. Examine the degradation characteristics of strain Y9 on diesel oil under the influence of nuclides and irradiation. In a single nuclide medium, strain Y9 exhibited a high degradation rate of 90.64% toward 1% diesel oil concentration. The addition of a radiation-resistant strain R1 can enhance the degradation efficiency of Y9 toward diesel oil.

New insights into uranium biomineralization mediated by Pseudomonas sp. WG2-6 in the presence of organic phosphorus: Promoting effect of extracellular polymeric substance and formation of U-P nanominerals

Microbial biomineralization significantly affects the uranium (U) behavior in the environment. However, the mechanism of microbial biomineralization of U is still not fully understood. In this study, a dominant bacterium (Pseudomonas sp. WG2-6) was isolated from U tail mining area. Abiotic precipitation tests demonstrated that U biomineralization was entirely attributed to the mediation of Pseudomonas sp. WG2-6 when the concentration ratio of exogenous β-glycerophosphate (SGP) to U was 10:1. Pseudomonas sp. WG2-6 exhibited strong immobilization ability towards U (97.59 %) according to batch experiments, and acylamide, carbonyls, and phosphate groups were the main functional groups that interacted with U. Besides, U mainly existed in the form of amorphous U-P complexes after biomineralization by Pseudomonas WG2-6, which could be converted into crystalline nano-minerals H2(UO2)2(PO4)2·8H2O in the presence of SGP. In particular, the formation and structural composition changes of extracellular polymeric substance (EPS) as well as the decrease in U4f binding energy were observed during the U biomineralization process of Pseudomonas sp. WG2-6 in the presence of SGP, indicating that EPS provided the nucleation site for the formation of stable biomineralized products. This work provides new insight into the mechanism of U microbial biomineralization and a theoretical basis for the remediation of U contaminated environments through microbial biomineralization.

Detoxification of Acrylamide by Potentially Probiotic Strains of Lactic Acid Bacteria and Yeast

Some potentially probiotic strains of lactic acid bacteria (LAB) and yeast that inhabit the digestive tract of humans are known to detoxify xenobiotics, including acrylamide (AA). The objective of the subsequent research was to evaluate the AA-detoxification capability of LAB and yeast isolated from various sources. Namely, the effect of AA was tested on the growth of LAB and yeast strains, as well in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Subsequently, the AA-binding ability of LAB and yeast was investigated in various environments, including the pH, incubation temperature, cell density, and with inanimate cells. The ability of selected LAB and yeast to reduce the genotoxicity of AA was tested on Caco-2 and Hep-G2 cell lines. The results showed that all tested strains exhibited strong resistance to AA at concentrations of 5, 10, and 50 µg/mL. Also, AA was detected in the intracellular and membrane extracts of tested strains. The most effective binding strain was Pediococcus acidilactici 16 at pH = 5, cell density = 109 CFU/mL, and incubation temperature = 37 °C (87.6% of AA removed). Additionally, all tested strains reduced the genotoxicity of AA, with the greatest reduction observed at the highest concentration of 50 µg/mL. The phenomena of detoxification by potentially probiotic strains could reduce the toxic and harmful effects of AA exposure to humans every day.

Effects of Detoxifying Substances on Uranium Removal by Bacteria Isolated from Mine Soils: Performance, Mechanisms, and Bacterial Communities

In this study, we investigated the effect of detoxifying substances on U(VI) removal by bacteria isolated from mine soil. The results demonstrated that the highest U(VI) removal efficiency (85.6%) was achieved at pH 6.0 and a temperature of 35 °C, with an initial U(VI) concentration of 10 mg/L. For detoxifying substances, signaling molecules acyl homoserine lactone (AHLs, 0.1 µmol/L), anthraquinone-2, 6-disulfonic acid (AQDS, 1 mmol/L), reduced glutathione (GSH, 0.1 mmol/L), selenium (Se, 1 mg/L), montmorillonite (MT, 1 g/L), and ethylenediaminetetraacetic acid (EDTA, 0.1 mmol/L) substantially enhanced the bacterial U(VI) removal by 34.9%, 37.4%, 54.5%, 35.1%, 32.8%, and 47.8% after 12 h, respectively. This was due to the alleviation of U(VI) toxicity in bacteria through detoxifying substances, as evidenced by lower malondialdehyde (MDA) content and higher superoxide dismutase (SOD) and catalase (CAT) activities for bacteria exposed to U(VI) and detoxifying substances, compared to those exposed to U(VI) alone. FTIR results showed that hydroxyl, carboxyl, phosphorus, and amide groups participated in the U(VI) removal. After exposure to U(VI), the relative abundances of Chryseobacterium and Stenotrophomonas increased by 48.5% and 12.5%, respectively, suggesting their tolerance ability to U(VI). Gene function prediction further demonstrated that the detoxifying substances AHLs alleviate U(VI) toxicity by influencing bacterial metabolism. This study suggests the potential application of detoxifying substances in the U(VI)-containing wastewater treatment through bioremediation.

Efficient enrichment of uranium (VI) in aqueous solution using magnesium-aluminum layered double hydroxide composite phosphate-modified hydrothermal biochar: Mechanism and adsorption

This study presents the successful synthesis of Magnesium-aluminum layered double hydroxide composite phosphate-modified hydrothermal biochar for efficient removal of U(VI) from aqueous solutions. A novel synthesis approach involving phosphate thermal polymerization-hydrothermal method was employed, deviating from conventional pyrolysis methods, to produce hydrothermal biochar. The combination of solvent thermal polymerization technique with hydrothermal process facilitated efficient loading of layered double hydroxide (LDH) components onto the biochar surface, ensuring simplicity, low energy consumption and enhanced modifiability. Bamboo waste was utilized as the precursor for biochar, highlighting its superior green and sustainable characteristics. Additionally, this study elucidated the interactions between phosphate-modified hydrothermal biochar and LDH components with U(VI). Physicochemical analysis demonstrated that the composite biochar possessed a high surface area and abundant oxygen-containing functional groups. XPS and FTIR analyses confirmed the efficient adsorption of U(VI), attributed to chelation interactions between phosphate groups, magnesium hydroxyl groups, hydroxyl groups and U(VI), as well as the co-precipitation of U(VI) with multi-hydroxyl aluminum cations captured by LDH. The composite biochar reached adsorption equilibrium with U(VI) within 80 min and exhibited excellent fitting to the pseudo-second-order kinetic model and Langmuir model. Under conditions of pH = 4 and 298 K, it displayed significantly high maximum adsorption capacity of approximately 388.81 mg g⁻1, surpassing untreated biochar by 17-fold. The adsorption process was found to be endothermic and spontaneous and even after five consecutive adsorption-desorption cycles, the removal efficiency of U(VI) remained stable at 75.46%. These findings underscore the promising application prospects of Magnesium-aluminum layered double hydroxide composite phosphate-modified hydrothermal biochar in efficiently separating U(VI) from uranium-containing wastewater, emphasizing its environmental and economic value.

One-step synthesis of phospho-rich, silica-enhanced chitosan aerogel for the efficient adsorption of uranium(VI)

In this study, an amorphous silica reinforced, phosphoric-crosslinked chitosan foam (P-CTS@SixOy) was prepared. The introduction of amorphous silica not only increased the affinity of the adsorbent for uranium, but also improved the stability of the material. The number of active sites of P-CTS@SixOy was increased by the introduction of phosphate groups. The material exhibited excellent uranium adsorption performance with the removal capacity and efficiency of 850.5 mg g-1 and 98.1 %, respectively. After regenerations, the morphology of P-CTS@SixOy still maintained, and the uranium adsorption efficiency remained above 90 %, manifesting the excellent cycle performance of P-CTS@SixOy. In the dynamic adsorption experiment, P-CTS@SixOy successfully concentrated the volume of uranium-containing solution, and exhibited excellent uranium adsorption performance. The analysis of kinetics, isotherms, and thermodynamics manifested that the uranium adsorption behavior of P-CTS@SixOy was a spontaneous, endothermic, monolayer chemical adsorption process. X-ray photoelectron spectroscopy, Scanning Electron Microscope, and Fourier Transform Infrared Spectrometer were used to characterized the P-CTS@SixOy before and after adsorption, which demonstrated that the main interaction mechanism between uranium and P-CTS@SixOy was the complexation. These studies indicated the huge application prospect of P-CTS@SixOy in the treatment of large-scale uranium-containing wastewater.

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.

Enhanced production of bacterial cellulose employing banana peel as a cost-effective nutrient resource

Bacterial cellulose (BC) is an exopolysaccharide produced by bacteria that has unusual structural features and is more refined than plant cellulose. BC has recently gained more attention in a variety of fields including biological and biomedical applications due to its excellent physiochemical properties including easy biodegradability, better water holding capacity, high tensile strength, high thermal stability, and high degree of polymerization. However, application of BC at industrial scale is still limited due to its high production cost and lesser yielding strains. The present study is an attempt to isolate and characterize a novel BC-producing bacterial strain. The bacterial strain S5 has resulted into maximum cellulose production of 4.76 ± 0.49 gL-1 (30°C, pH 7.0). The strain has been further identified as Stenotrophomonas sp. Derivation of nutritional and cultural conditions has resulted into 2.34-fold enhanced BC production (banana peel powder, peptone, tartaric acid, pH 7, 30°C). FTIR spectrum of BC revealed characteristic absorption bands which could be attributed to the O-H band, C-H stretching, C-O-C stretching band, O-H bending, and >CH2 bending, indicative of the β-1,4 glycosidic linkages of cellulose. Thermogravimetric analysis has also revealed stability of polysaccharide backbones and characteristic weight loss points. Employment of banana peel powder has appeared as a proficient low-cost source for large-scale economic production of BC for industrial applications.

"One-can" strategy for the synthesis of hydrothermal biochar modified with phosphate groups and efficient removal of uranium(VI)

Significant selectivity, reasonable surface modification and increased structural porosity were three key factors to improve the competitiveness of biochar in the adsorption field. In this study, a hydrothermal bamboo-derived biochar modified with phosphate groups (HPBC) was synthesized using "one-can" strategy. BET showed that this method could effectively increase the specific surface area (137.32 m2 g-1) and simulation of wastewater experiments indicated HPBC had an excellent selectivity for U(VI) (70.35%), which was conducive to removal of U(VI) in real and complex environments. The accurate matchings of pseudo-second-order kinetic model, thermodynamic model and Langmuir isotherm showed that at 298 K, pH = 4.0, the adsorption process dominated by chemical complexation and monolayer adsorption was spontaneous, endothermic and disordered. Saturated adsorption capacity of HPBC could reach 781.02 mg g-1 within 2 h. The introduction of phosphoric acid and citric acid by "one-can" method not only provided abundant -PO4 to assist adsorption, but also activated oxygen-containing groups on the surface of the bamboo matrix. Results showed that adsorption mechanism of U(VI) by HPBC included electrostatic action and chemical complexation involving P-O, PO and ample oxygen-containing functional groups. Therefore, HPBC with high phosphorus content, outstanding adsorption performance, excellent regeneration, remarkable selectivity and green value provided a novel solution for the field of radioactive wastewater treatment.

Surface Engineering Design of Nano FeS@Stenotrophomonas sp. by Ultrasonic Chemical Method for Efficient U(VI) and Th(IV) Extraction

Nano-FeS has great potential for use in the management of radioactive contaminants. In this paper, we prepared a FeS@Stenotrophomonas sp. composite material by ultrasonic chemistry, and it showed excellent removal of uranium and thorium from the solution. Through optimization of the experimental conditions, it was found that the maximum adsorption capacities for uranium and thorium reached 481.9 and 407.5 mg/g for a composite made with a synthetic ratio of 1:1, pH 5 and 3.5, respectively, for U and Th, and sonication for 20 min. Compared with those of FeS or Stenotrophomonas alone, the removal capacity was greatly improved. The results of a mechanistic study indicated that efficient removal of the uranium and thorium was due to ion exchange, reduction, and microbial surface adsorption. FeS@Stenotrophomonas sp. could be applied to U(VI) and Th(IV) extraction for radioactive water.