Search Results (62)

Microbially induced carbonate precipitation (MICP) is a sustainable biomineralization technology with extensive potential in environmental remediation, geotechnical engineering, and materials science, characterized by its eco-friendliness, low energy consumption, and high compatibility. This paper systematically reviews the biochemical mechanisms, critical influencing factors, and recent engineering advancements of MICP. We first explore the metabolic pathways driven by urease and carbonic anhydrase (CA), emphasizing the synergistic effects of microbial strain selection and environmental parameters—such as temperature, pH, and substrate composition—on mineralization efficiency. Furthermore, the review evaluates the latest application cases, including the immobilization of heavy metals and radionuclides, remediation of building materials, soil stabilization, CO₂ sequestration, and the fabrication of novel biomaterials, highlighting MICP’s role in enhancing engineering performance while mitigating environmental risks. By comparing the cost and sustainability of MICP against traditional chemical methods, this paper identifies current technological bottlenecks—such as reaction efficiency and material brittleness—and proposes future research directions, including synthetic biology for strain optimization and artificial intelligence-assisted design for site-specific applications. Ultimately, this review provides a theoretical framework to guide basic research and promote innovative, scalable deployment of MICP in sustainable technology sectors. Full article

Sunflower (Helianthus annuus) can potentially be used for uranium (U) phytoremediation. However, the influence of arbuscular mycorrhizal fungi (AMF) on key rhizosphere processes and plant U uptake remains insufficiently researched. We hypothesized that AMF inoculation could enhance sunflower tolerance to U stress by improving plant physiological performance and modifying rhizosphere properties. To test this hypothesis, this study examined the effects of AMF (Funneliformis mosseae, Glomus etunicatum, and their co-inoculation) on sunflowers under U stress, encompassing plant growth and physiological traits, rhizosphere properties, enzyme activities in the rhizosphere soil, uranium speciation in the rhizosphere soil, and the accumulation and distribution of uranium within the plant. Results showed that AMF successfully colonized the roots, enhancing plant growth, biomass, and gas exchange, while improving photosynthetic efficiency and reducing non-photochemical quenching. In the rhizosphere, AMF elevated soil respiration, organic matter, dissolved organic carbon, and microbial biomass carbon; improved phosphatases, urease, catalase, and sucrase activities; also reshaped U speciation, increasing exchangeable and carbonate-bound fractions while decreasing those bound to organic matter, Fe/Mn oxides, and residual phases. Moreover, AMF reduced U concentration in leaves and stems, promoted U retention in belowground tissues, and significantly lowered the U translocation factor. These findings demonstrate that AMF inoculation improves sunflower tolerance to U stress by enhancing physiological performance, modifying rhizosphere properties, and immobilizing U in roots, supporting its potential use in phytoremediation strategies for U-contaminated environments. Full article

Enzyme-Induced Carbonate Precipitation (EICP) represents a sustainable advancement in geotechnical engineering for stabilizing fine-grained soils (e.g., silt). Utilizing plant-derived urease (~12 nm) to catalyze urea hydrolysis, this technique generates calcium carbonate (CaCO₃) for soil reinforcement. Unlike Microbially Induced Carbonate Precipitation (MICP), EICP overcomes microbial size constraints (0.5–3 µm) by penetrating soil micropores, enabling uniform cementation. Its innovative single-phase low-pH method achieves >98% calcium conversion efficiency, yielding 6.41 MPa unconfined compressive strength (UCS) in sand—a 92.97% improvement over MICP. EICP demonstrates versatility: enhancing soil strength (up to 650% for silt), erosion resistance (wind erosion modulus increased ~20-fold), anti-seepage performance (permeability reduced from 10⁻⁶ to <10⁻⁹ cm/s), and heavy metal immobilization (>99%). However, challenges include unstable crystal morphologies (e.g., excessive vaterite), urease stability/cost constraints, and environmental concerns related to NH₃ emissions from urea hydrolysis. The manuscript acknowledges these emissions’ impacts and introduces mitigation strategies: ammonia capture technologies, optimized dosing protocols, and exploration of alternative N-sources. Long-term durability data under complex field conditions remain insufficient. Ongoing research addresses these gaps through nucleating agents (dried skim milk, biochar), enzyme immobilization, process optimization, and byproduct treatment. As a low-carbon technology with targeted mitigation measures, EICP advances environmentally conscious soil stabilization practices. This study presents a comparative narrative analysis of EICP’s performance and challenges, integrating laboratory findings and field applications. Full article

Nickel (Ni) contamination threatens plant growth and ecosystem stability, and plant-growth-promoting rhizobacteria (PGPR) are sustainable bioremediation candidates. Here, we isolated and characterized a Ni-resistant PGPR strain, Microbacterium algeriense C14, from the rhizosphere of Zinnia elegans in Ni-contaminated soil. C14 exhibited exceptional Ni tolerance (up to 800 mg·L⁻¹), produced indole-3-acetic acid (IAA), and maintained pH homeostasis (8.3–8.7). XPS and XRD analyses confirmed a novel carboxylate-based precipitation mechanism: C14 secretes carboxyl-containing metabolites that coordinate with Ni²⁺ to form stable amorphous nickel–carboxylate complexes. Under Ni stress (50–600 mg·L⁻¹ for germination; 50–600 mg·kg⁻¹ soil for pot experiments), C14 inoculation increased the seed germination index by up to 47.3%, seedling root length by 36.9%, and mature plant aboveground fresh weight by 21.32%, while reducing plant Ni uptake by 38.7% (seedlings) and 49.9% (mature shoots). It also enhanced plant antioxidant-enzyme (SOD and POD) activities and soluble protein content, improved soil quality (pH +0.16–0.33 units, urease/acid phosphatase activities elevated), and reduced soil-available Ni by 23.7%. Additionally, C14 enriched Proteobacteria in the rhizosphere and modified microbial community structure. These results highlight M. algeriense C14 as a promising resource for Ni-contaminated soil remediation via integrated metal immobilization, growth promotion, and rhizosphere regulation. Full article

The increasing demand for continuous physiological monitoring has accelerated the development of high-sensitivity wearable electrochemical platforms. This study reports the fabrication of a multi-analyte electrochemical sensor based on single-walled carbon nanotubes (SWCNTs) for the detection of sweat-associated metabolites. To facilitate efficient heterogeneous electron transfer, glucose oxidase (Gox), lactate oxidase (Lox), and urease (Ure) were immobilized onto the SWCNT network through π–π interaction using 1-pyrenebutanoic acid succinimidyl ester (PBSE), followed by additional stabilization via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling. The developed platform exhibited concentration-dependent resistance responses within the ranges of 0.02–0.20 mM for glucose, 20–100 mM for lactate, and 50–400 mM for urea under controlled experimental conditions. The resistance-based configuration enabled stable and reproducible signal modulation across these concentration intervals. Although direct testing with human sweat was not performed, the electrochemical behavior of key sweat-related metabolites was systematically evaluated as a preparatory step toward future wearable integration. Full article

A simplified kinetic model for the quantitative analysis of a potentiometric, pH-based urea biosensor is presented. The device was an electrolyte–insulator–semiconductor capacitor (EISCAP) with a pH-sensitive Ta₂O₅ gate functionalized by a polyallylamine hydrochloride (PAH)/urease bilayer. Within the steady-state approximation, the kinetic equations yielded an implicit algebraic relation linking the bulk urea concentration to the local pH at the sensor surface. Numerical solution of this equation, combined with a fitting routine, provides the apparent Michaelis–Menten constant ($K_M$) and the normalized maximum reaction rate (${\overline{k}}_V$). Validation against the literature data confirmed the reliability of the approach. Experimental results were then analyzed in both phosphate buffer (PBS) and artificial urine (AU), covering urea concentrations of 0.1–50 mM. The fitted parameters showed comparable $K_M$ values of 10.9 mM (PBS) and 32.4 mM (AU), but strongly different ${\overline{k}}_V$ values: $2.2\times {10}^{-4}$ (PBS) versus $8.6\times {10}^{-7}$ (AU). The three-order reduction in AU was attributed to the inhibitory effects inherent to complex biological fluids. These findings highlight the importance of the model-based quantitative analysis of EISCAP biosensors, enabling the accurate characterization of immobilized enzyme layers and guiding optimization for applications in realistic sample matrices. Full article

A nanoliter-scale fabrication method was applied to construct a colorimetric lateral flow strip for urea detection (Urea-CLFS). The device involves two main papers: a nitrocellulose membrane (NC-Mb) for urease enzyme immobilization and chromatography paper (CH-PP) containing a phenol red indicator. Urea-CLFS is a tool for detecting urea that is based on enzyme catalysis and the change in color of phenol red when urea is present. The Urea-CLFS fabrication was made possible by the minimal amount of nanoliters used in reagent consumption. The use of small arrays of phenol red dots provides a higher response result compared to single dots applied on CH-PP. To find the most effective design, it analyzed how urease was aligned on NC-Mb horizontally and vertically. According to our findings, the vertical alignment of the urease enzyme on NC-Mb leads to a prolonged reaction time, which leads to higher product production. The optimization process included optimizing various parameters, including the layer number of phenol red on CH-PP, phenol red concentration, urease concentration, reaction time, and sample volume. Under optimal conditions, the Urea-CLFS provided a linear range of 0.25–8.0 mmol L⁻¹ with an LOD of 0.34 mmol L⁻¹, which is sufficient for human health diagnostics. The accuracy of the Urea-CLFS was demonstrated by the recovery of the human urine sample between 95 ± 3% and 103 ± 3% (n = 3). Full article

Background: Cadmium (Cd) pollution poses a significant environmental challenge. Microbially induced carbonate precipitation (MICP), an advanced bioremediation approach, relies on the co-precipitation of soluble metals with the microbial hydrolysate from urea. This study isolated a urease-producing strain and evaluated its Cd remediation potential. Methods: The isolated strain UA7 was identified through 16S rDNA gene sequencing. Urease production was enhanced by optimizing the culture conditions, including temperature, dissolved oxygen levels—which were affected by the rotational speed and the design of the Erlenmeyer flask, and the concentration of urea added. Its Cd remediation efficacy was assessed both in water and soil. Results: UA7 was identified as Lysinibacillus sp., achieving peak urease activity of 188 U/mL. The immobilization rates of soluble Cd reached as high as 99.61% and 63.37%, respectively, at initial concentrations of 2000 mg/L in water and 50 mg/kg in soil. The mechanism of Cd immobilization by strain UA7 via MICP was confirmed by the microstructure of the immobilized products with attached bacteria, characteristic absorption peaks, and the formed compound Ca_0.67Cd_0.33CO₃, which were analyzed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The Cd-remediation effect of strain UA7, which reduces lodging in wheat plants, prevents the thinning and yellowing of stems and leaves, and hinders the transition of soluble Cd to the above-ground parts of the plant, was also demonstrated in a pot experiment. Conclusions: Therefore, Lysinibacillus sp. UA7 exhibited high potential for efficiently remediating contaminated Cd. Full article

Optimizing seeding ratios in mixed cover crop species can maximize their ecological benefits, such as soil properties and weed suppression. A two-year field study assessed seven oat (O) and daikon radish (D) ratios (100:0 to 0:100) for their effects on soil quality, weed pressure, and subsequent spinach yield. Measured parameters included cover crop biomass, C:N ratio, land equivalence ratio (LER), soil organic carbon (SOC), microbial population, soil enzyme activities, bulk density, porosity, moisture, and water infiltration time. The impact of intercrop residues and two weeding strategies (hand weeding and no weeding) on weed pressure and spinach yield was also assessed. Oat monoculture produced the highest biomass (338.7 g m⁻²), while radish monoculture biomass was the lowest (256.1 g m⁻²). Yet the 30:70 (O:D) ratio contributed to the highest SOC (0.96). The C:N ratio of all intercropped combinations was below the critical threshold (25:1) that causes N immobilization, with oat monoculture having the highest value (23:1). The microbial population was highest with the 10:90 (O:D) ratio, with 12.8 × 10⁻⁴ most probable number per g⁻¹ soil. While urease and dehydrogenase enzyme activities were not affected by intercrop ratios, β-glucosidase and alkaline phosphatase activities were up to 30% higher in daikon radish-dominated intercrops. Bulk density decreased by 31.7% in oat monoculture, whereas infiltration time was shortened in daikon radish monoculture by 41.7% (4.6 s). Weed suppression was strongest in oat monoculture and the 90:10 (O:D) intercropping, reducing weed populations by over 30%. Spinach yield was highest in oat monoculture with hand weeding (842.9 g m⁻²), with a 40.2% increase over weeding alone. Overall, daikon radish-dominated intercropping ratios were more effective in enhancing soil properties, whereas oat-dominated intercropping improved spinach yield, mainly due to slower decomposition, thus better suppressing weeds. Full article

Phytoremediation is widely acknowledged as a viable method for soil remediation; however, its efficacy remains limited in soils co-polluted with petroleum hydrocarbons and heavy metals. To overcome this constraint, the present study explored an innovative approach utilizing ferrate-modified biochar (FeBC) to augment phytoremediation efficiency. Experimental findings revealed that ferrate treatment markedly modified the physicochemical characteristics of biochar, yielding thinner, smoother-surfaced structures with pronounced iron enrichment. At a 5% application rate alongside ryegrass cultivation, FeBC exhibited superior remediation performance, achieving 52.0% degradation of petroleum hydrocarbons (notably within the meso-aggregate fraction) and a 19.2% decline in zinc bioavailability via immobilization, thereby reducing zinc uptake in ryegrass tissues. Furthermore, FeBC amendment induced significant shifts in rhizosphere soil biochemistry and microbial ecology, characterized by diminished catalase activity but elevated urease and alkaline phosphatase activities. Phospholipid fatty acid profiling indicated a substantial rise in bacterial biomass (encompassing both Gram-positive and Gram-negative groups), particularly in meso- and micro-aggregates, whereas soil bacterial α-diversity declined markedly, accompanied by distinct compositional changes across aggregate size fractions. These results offer mechanistic insights into the synergistic interaction between FeBC and ryegrass in co-contaminated soil rehabilitation, the aggregate-dependent distribution of remediation effects, and microbial community adaptations to FeBC treatment. Collectively, this study advances the understanding of ferrate-modified biochar’s role in phytoremediation enhancement and clarifies its operational mechanisms in petroleum-zinc co-contaminated soil systems. Full article

Heavy metal-contaminated soil poses a severe threat to environmental quality and human health, calling for eco-friendly and efficient remediation strategies. This study explored the use of biochar-immobilized copper-resistant Pseudomonas aeruginosa to remediate copper-contaminated soil and promote growth of Chinese milk vetch (Astragalus sinicus L.). Indoor pot experiments compared four groups: copper-contaminated soil (control), soil with biochar, soil with free bacteria, and soil with biochar-immobilized bacteria (IM). Results showed IM had the most significant effects on soil properties: it raised pH to 7.04, reduced bioavailable copper by 34.37%, and increased catalase (3.48%) and urease (78.95%) activities. IM also altered soil bacterial communities, decreasing their richness and evenness (alpha diversity) while shifting community composition. For Chinese milk vetch, IM reduced leaf malondialdehyde (a marker of oxidative stress) by 15%, increased total dry weight by 90%, and lowered copper accumulation in roots (18.62%) and shoots (60.33%). As a nitrogen-fixing plant, the vetch’s nitrogen fixation in roots and shoots rose by 82.70% and 57.08%, respectively, under IM. These findings demonstrate that biochar-immobilized Pseudomonas aeruginosa is a promising in situ amendment for remediating copper-contaminated soil and boosting plant growth. Full article

Petroleum-contaminated soil is an increasingly severe environmental issue. The integration of phytoremediation and microbial remediation can effectively mitigate their individual limitations and enhance remediation efficiency. In this study, four newly isolated bacterial strains (including Cytobacillus and Rhodococcus) that exhibited preferential degradation of distinct petroleum components were combined with the rhamnolipid-producing strain Pseudomonas aeruginosa SL-1. The immobilization of this petroleum-degrading microbial consortium was performed by biochar adsorption and sodium alginate embedding, subsequently optimized using response surface methodology (0.75 g·L⁻¹ of biochar, 40 g·L⁻¹ of sodium alginate, and 40 g·L⁻¹ of calcium chloride). The results showed that the highest petroleum degradation rate (97.1%) of immobilized bacterial consortium was achieved at 72 h at a petroleum concentration of 5.0 g·L⁻¹. When combined with Sudan grass for soil bioremediation, the degradation rate reached 72.8% after 120 d for soil containing 5.0 g·kg⁻¹ of petroleum, higher than the results for the treatments with only immobilized bacterial consortium (53.0%) or Sudan grass (49.2%). Furthermore, significant improvements were observed for soil pH; nitrogen, phosphorus, and potassium contents; and urease, dehydrogenase, and catalase activities. Composite treatment also significantly increased the diversity and richness of the soil bacterial community and regulated its structure, function, and network composition. This study offers theoretical insights and potential practical applications for the enhanced bioremediation of petroleum-contaminated soils. Full article

Plant growth-promoting rhizobacteria (PGPR) have significant potential for enhancing soil quality and plant growth; however, their agricultural application is limited by challenges such as immobilization and desiccation vulnerability. Background: This study addressed PGPR solid formulation by applying JetCutter-assisted immobilization technology to PGPR strains isolated from the rhizosphere of hazelnut (Corylus avellana). Methods: Four immobilized PGPR strains were evaluated under controlled greenhouse conditions: Serratia proteamaculans, Pseudomonas mohnii, Pseudomonas baetica, and Bacillus safensis. Their effects on root development, gas exchange parameters, dissolved organic carbon (DOC), and soil enzymatic activities (phosphatase, urease, protease, and β-glucosidase) were assessed. Principal component analysis (PCA) was used to identify the top-performing strain. Results: Treatment with encapsulated bacteria resulted in a 27% increase in DOC compared to controls (p < 0.05), while phosphatase and urease activities increased by 35% and 28%, respectively. Root length and volume improved by 18% and 22%, respectively, with PCA identifying P. baetica as the most effective strain. Conclusions: Immobilized Gram-negative PGPR strains enhanced root development and soil biochemical activity in hazelnuts, whereas B. safensis enhanced photosynthesis but had minimal impact on soil properties. These results highlight functional differences and support the use of PGPR immobilization to promote early plant establishment. Full article

The bioavailability of heavy metals is profoundly influenced by their interactions with active soil components (microorganisms, organic matter, and iron minerals). However, the effects of urease-producing bacteria combined with organo-Fe hydroxide coprecipitates (OFCs) on Cd accumulation in wheat, as well as the mechanisms underlying these effects, remain unclear. In this study, pot experiments integrated with high-throughput sequencing were employed to investigate the impacts of the urease-producing bacterial strain TJ6, ferrihydrite (Fh), and OFCs on Cd enrichment in wheat grains, alongside the underlying soil–microbial mechanisms. The results demonstrate that the strain TJ6-Fh/OFC consortium significantly (p < 0.05) reduced (50.1–66.7%) the bioavailable Cd content in rhizosphere soil while increasing residual Cd fractions, thereby decreasing (77.4%) Cd accumulation in grains. The combined amendments elevated rhizosphere pH (7.35), iron oxide content, and electrical conductivity while reducing (14.5–21.1%) dissolved organic carbon levels. These changes enhanced soil-colloid-mediated Cd immobilization and reduced Cd mobility. Notably, the NH₄⁺ content and NH₄⁺/NO₃⁻ ratio were significantly (p < 0.05) increased, attributed to the ureolytic activity of TJ6, which concurrently alkalinized the soil and inhibited Cd uptake via competitive ion channel interactions. Furthermore, the relative abundance of functional bacterial taxa (Proteobacteria, Gemmatimonadota, Enterobacter, Rhodanobacter, Massilia, Nocardioides, and Arthrobacter) was markedly increased in the rhizosphere soil. These microbes exhibited enhanced abilities to produce extracellular polymeric substances, induce phosphate precipitation, facilitate biosorption, and promote nutrient (C/N) cycling, synergizing with the amendments to immobilize Cd. This study for the first time analyzed the effect and soil science mechanism of urease-producing bacteria combined with OFCs in blocking wheat’s absorption of Cd. Moreover, this study provides foundational insights and a practical framework for the remediation of Cd-contaminated wheat fields through microbial–organic–mineral collaborative strategies. Full article

Soil heavy-metal pollution is one of the most serious environmental issues in the world. There is an urgent need to develop feasible strategies for the remediation of polluted soil. Biochar has great potential to reduce heavy metal phytotoxicity and promote plant growth, but its mechanisms are still unclear. In this study, phosphoric acid and magnesium composite-modified tea branch biochar (PMB) was prepared and characterized. The effects of PMB at 5% addition on pakchoi growth, Cd/Pb accumulation and subcellular distribution in pakchoi, soil physicochemical characteristics and enzyme activities, Cd/Pb bioavailability, bacterial community structure, and diversity in Cd/Pb co-contaminated soils was investigated by a pot experiment. The results showed that PMB significantly alleviated the phytotoxicity of Cd and Pb. The application of PMB effectively increased the plant height and biomass and Cd and Pb proportion in the cell wall, while reducing Cd and Pb accumulation and their distribution in cytoplasm and organelles in pakchoi plants. PMB significantly improved the activities of urease, invertase, and catalase and reduced the available Cd and Pb contents in soil. Moreover, PMB changed the structure and diversity of the soil bacterial community. The relative abundance of several beneficial microbial phyla, including Acidobacteriota, Bacteroidota, Actinobacteriota, and Gemmatimonadota, increased by 13.81%, 19.02%, 68.09%, and 34.79%, respectively. The Shannon and Chao1 index also increased significantly. This study provides an effective strategy for simultaneous Cd and Pb immobilization in soil, promoting plant growth and inhibiting heavy metal accumulation in vegetables, which highlights the application of PMB in sustainable agro-ecosystems. Full article