Urease-producing Bacteria Research Articles

Improvement of the Sand Quality by Applying Microorganism Induced Calcium Carbonate Precipitation to Reduce Cement Usage

This research aimed to study the utilization of microorganisms in the soil. These microorganisms were applied to improve the quality of soil and sand to reduce cement consumption. The process of microbial-induced precipitation of calcium carbonate (MICP) was used in this study, a bonding process to create a binding between sand particles from the naturally occurring processes of microorganisms. The study was conducted to determine the maximum growth rate of bacteria (maximum growth curve) of five strains as follows Proteus mirabilis TISTR 100, Bacillus thuringiensis TISTR 126, Staphylococcus aureus TISTR 118, Bacillus sp. TISTR 658 and Bacillus megaterium TISTR 067 in Nutrient Broth (NB) culture medium at 37°C. Christensen's Urea Agar slant (UA) was a preliminary screen for urease-producing bacteria. The color change of indicator color was seen in the slant, comparing the results (+) and control (-). The researchers have selected bacterial strains capable of producing significant amounts of enzymes to hydrolyze urea. It was found that the amount of calcium carbonate sediment produced by five strains of bacteria, namely Proteus mirabilis TISTR 100, Bacillus thuringiensis TISTR 126, Staphylococcus aureus TISTR 118, Bacillus sp. TISTR 658 and Bacillus megaterium TISTR 067 had the amount of sediment produced as follows: 3.430, 3.080, 2.590, 1.985, and 1.615 mg/ml, respectively. It was found that the species Bacillus sp. TISTR 658 does not produce the most calcium carbonate sediment. Nevertheless, it made the sand samples stick together tightly and form the perfect lumps. Therefore, improving the sand's composition has shown the potential to apply the MICP process to reduce the cement used.

Evolution in the Understanding of the Etiology of Staghorn Renal Lithiasis

Staghorn lithiasis, characterized by renal calculi that extensively occupy the renal collecting system, poses significant medical challenges due to high morbidity and mortality rates. Traditionally attributed primarily to recurrent urinary tract infections caused by urease-producing bacteria, recent studies indicate a shift toward an increased prevalence of metabolic stones. This change may be linked to rising obesity and metabolic syndrome rates. Historical perspectives emphasized struvite stones, associated with infections, but emerging data reveal a notable proportion of calcium phosphate and mixed stones, suggesting a complex interplay between metabolic factors and infection. Analysis of stone composition in patients has shown that metabolic abnormalities are common, emphasizing the need for comprehensive evaluations beyond infectious risk. Understanding this evolving etiology is crucial for guiding treatment and improving patient outcomes.

Immobilization of Cadmium Via Ureolytic Bacteria Isolated from Greywater Waste and Horse Faeces

With the constant growth of technology and pollution caused by urban expansion, heavy metal contamination has become an alarming concern. The performance of Microbial induced carbonate precipitation technology in immobilizing heavy metal has been demonstrated by several researchers. While various studies have successfully isolated ureolytic bacteria from a variety of sources, there are very limited studies that have focused on isolating them from local waste sources, specifically Greywater and Horse Faeces for MICP application, which benefits in terms of economical, sustainability, and efficiency for engineering purposes. The study aims to investigate the effect of urease-producing bacteria derived from Greywater and horse faeces on heavy metal immobilization. The methods include collecting waste samples, isolating and subculturing of ureolytic bacteria, testing the physiological characteristics of ureolytic bacteria, examining the tolerance test and evaluating heavy metal removal efficacy through Atomic Absorption Spectrophotometry (AAS) analysis, and last but not least, Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) analyses of morphological and mineralogical properties of biominerals formed after heavy metal immobilization treatment. The study found that bacteria from Greywater were more effective at heavy metal immobilization than those from Horse Faeces. Additionally, AAS analysis indicates the greywater-derived bacteria from the residential area sample's exceptional competence in Cd2+ removal, with a significant 80.19% removal rate exceeding the horse faeces bacteria sample's removal rate of 65.26%. The morphological analysis confirmed the presence of heavy metal carbonate in treated heavy metal samples, as well as presenting insight into the effectiveness and application of local ureolytic bacteria's potential for heavy metal toxicity degradation.

Bhargavaea beijingensis a promising tool for bio-cementation, soil improvement, and mercury removal

Microbially Induced Calcite Precipitation (MICP) has emerged as a promising technique for bio-cementation, soil improvement, and heavy metal remediation. This study explores the potential of Bhargavaea beijingensis, a urease-producing bacterium, for these applications. Six ureolytic bacteria were isolated from calcareous bricks mine soil and screened for urease and calcite production. B. beijingensis exhibited the highest urease activity and calcite precipitation. Urease activity, calcite precipitation, sand solidification, heavy metal removal efficiency, and compressive strength were evaluated. It showed significant heavy metal removal efficiency, particularly highest for HgCl2. Mortar blocks treated with B. beijingensis or its crude enzyme exhibited improved compressive strength, suggesting its potential for bio-cementation. Crack remediation tests demonstrated successful crack healing in mortar blocks using the bacterium or its enzyme. This study identifies B. beijingensis as a novel and promising MICP agent with potential applications in bio-cementation, soil improvement, and heavy metal remediation. Hence, B. beijingensis diversified abilities prove superior performance compared to commonly used strains like Bacillus subtilis and Shewanella putrefaciens in bio-cementation applications. Its high urease activity, calcite precipitation, and heavy metal removal abilities make it a valuable candidate for sustainable and eco-friendly solutions in various fields.

Microbially Induced Calcium Carbonate Precipitation UsingLysinibacillussp.: A Ureolytic Bacteriumfrom Uttarakhand for Soil Stabilization.

Microbially induced calcium carbonate precipitation (MICP) is a soil remediation method that has emerged as a viable and long-term solution for enhancing soil mechanical qualities. The technique of MICP that has been extensively researched is urea hydrolysis, which occurs naturally in the environment by urease-producing bacteria as part of their fundamental metabolic processes. The objectives of the current study include screening and identifying native ureolytic bacteria from soil in Uttarakhand, optimizing growth factors for increased urease activity, and calcite precipitation by the bacteria using response surface methodology. Additionally, it was assessed how well the isolated bacteria in the medium biomineralized when using synthetic media and cheaper alternatives such as cow urine and eggshell as sources of urea and Ca2+, respectively. The isolated strain identified as Lysinibacillus sp. was found to be the very active strain after soil samples were screened for ureolytic bacteria. It was discovered that optimization studies with values of pH 8, urea concentration (0.8M), inoculum concentration (3%), and incubation time (48h) yielded a higher activity of 33.7 U/mL (threefold increase), and a higher calcium carbonate precipitation (enzyme activity: 10.96 U/mL, pH: 8.92, soluble Ca2⁺: 25.53mM and insoluble Ca2⁺: 0.856g). The calcite precipitation in broth media supplemented with ready-made substrates and alternative sources demonstrated a similar result of increased pH and ammonia release. Thus, the current study successfully paves the way for several possibilities to stabilize the slopy soils prone to landslides and erosion in Uttarakhand and pinpoint an economic approach through biomineralization.

Influence of shear strength parameters on loose fine sand treated with coir fiber and microbially induced calcite precipitation

In recent years, there has been an increasing use of Microbially Induced Calcite Precipitation (MICP) technology in ground improvement. Adding fiber to bio-cemented sand leads to significant improvements in its properties. This paper examines how coir fiber and microbially induced calcite precipitation (MICP) might be used to improve the engineering qualities of fine sand. The sand was mixed with Coir fiber at varying Fiber Contents (FC) of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight of sand. Additionally, varied Aspect Ratios (AR) of 45, 90, 136, 182, and 227 were considered. The mixture also included urease-producing bacteria (Sporosarcina Pasteurii), as well as solutions of urea and calcium chloride with 3M molarity. The untreated and treated sand samples were submitted to a Direct Shear Test (DST). The study found that the shear strength parameters, such as the angle of internal friction, increased by 1.1 times compared to standard fine sand. Additionally, the angle of internal friction (ϕ) of fiber-reinforced sand with MICP showed 1.4 times increase, while the cohesion values demonstrated a sixfold increase compared to MICP fine sand. It was determined that the optimal aspect ratio was 182, and the optimal fiber content was 0.3%. Moreover, the Scanning Electron Microscope (SEM) was utilized to examine the calcite formations present in the treated sand samples, and calcite precipitation was observed between the pores of the soils.

Magnesium polypeptide combined with microbially induced calcite precipitation for remediation of lead contamination in phosphate mining wasteland soil

Soil Pb contamination is inevitable, as a result of phosphate mining. It is essential to explore more effective Pb remediation approaches in phosphate mining wasteland soil to ensure their viability for a gradual return of soil quality for cultivation. In this study, a Pb-resistant urease-producing bacterium, Serratia marcescens W1Z1, was screened for remediation using microbially induced carbonate precipitation (MICP). Magnesium polypeptide (MP) was prepared from soybean meal residue, and the combined remediation of Pb contamination with MP and MICP in phosphate mining wasteland soil was studied. Remediation of Pb using a combination of MP with MICP strain W1Z1 (WM treatment) was the most effective, with the least exchangeable Pb at 30.37% and the most carbonate-bound Pb at 40.82%, compared to the other treatments, with a pH increase of 8.38. According to the community analysis, MP moderated the damage to microbial abundance and diversity caused by MICP. Total nitrogen (TN) was positively correlated with Firmicutes, pH, and carbonate-bound Pb. Serratia inoculated with strain W1Z1 were positively correlated with bacteria belonging to the Firmicutes phylum and negatively correlated with bacteria belonging to Proteobacteria. The available phosphate (AP) in the phosphate mining wasteland soil could encapsulate the precipitated Pb by ion exchange with carbonate, making it more stable. Combined MP-MICP remediation of Pb contamination in phosphate mining wasteland soil was effective and improved the soil microenvironment.

Mechanical and microstructural properties of biogenic CaCO3 deposition (MICP) on a specific volcanic sediment (unwelded Tuffs) by Bacillus pasteurii and Bacillus subtilis

Microbially induced calcite precipitation has garnered significant attention in recent years as a promising and environmentally friendly process for addressing sand stabilization and soil consolidation. While its potential to stabilize sand dunes and mitigate soil liquefaction is well-documented, the applicability of MICP in the consolidation of stone materials has not been thoroughly investigated. Tuffs, which are silicate-laden pyroclasts, have historical significance as hybrid materials for cement, emphasizing their importance in cultural heritage. In previous MICP applications, there has been a lack of exploration regarding the incorporation of urease-producing bacteria (UPB) into Tuffs. Consequently, the potential of MICP in substrates such as Tuffs has been largely overlooked. The primary objective of this study is to assess the feasibility of incorporating UPB into Tuffs as a consolidating agent to facilitate calcium carbonate precipitation. We aim to investigate the microstructure of the resulting polymorphs and the previously unknown mechanism of increased resistance to W-D cycles in the treated samples at the nanoscale. In this study, we compared the cementation response of Tuff when subjected to two different UPBs by evaluating changes in key parameters, including capillary water absorption (CWA), cyclic tests such as wet-dry and salt attack, and uniaxial compressive strength. Furthermore, the characteristics of crust formation were examined using FESEM, and an in-depth analysis of the microstructure of the deposited bacterial CaCO3 was conducted. The mechanism of increased W-D resistance in Tuffs reinforced by MICP has not been previously addressed by researchers. Our study demonstrated that the increase in resistance to W-D cycles was more pronounced in samples treated with Bacillus pasteurii. Further FESEM analysis showed the presence of Bacillus pasteurii spores in the nanopores of the (W-D) exposed samples. N2 adsorption analysis revealed that nanopore alteration occurred only in samples treated with Bacillus pasteurii. Additionally, Tuffs are prone to disjoining pressure, which occurs in nanopores. Based on these observations, we postulate that the increased resistance to W-D cycles in the samples treated with Bacillus pasteurii was caused by a decrease in disjoining pressure due to the recrystallization of amorphous calcium carbonate (ACC) in the nanopores of the studied Tuff.

Exogenous inoculation with heavy metal-immobilizing bacteria roused the key rhizosphere bacterial community and metabolites of wheat to inhibit cadmium absorption

Rhizosphere functional microorganisms play an important role in the bioremediation of heavy metal-polluted farmlands, however, further research is needed to investigate the effects of exogenous inoculation of functional strains on key bacterial communities and metabolites in cadmium (Cd)-polluted wheat farmlands. This study investigated the effects of the urease-producing bacterium Enterobacter bugandensis TJ6 combined with polyamine-producing bacterium Serratia marcescens X43 on Cd uptake by wheat and its microbiological and soi biolological mechanisms. The results showed that strains TJ6+X43 reduced (95.1 %) the Cd content by secreting urease and polyamines and inducing the precipitation of Cd to form CdCO3 and Cd(OH)2. The combined strains increased (22.7 %) the dry weight and reduced (37.2 %) the Cd content in wheat grains. Moreover, the DTPA-Cd content, the NH4+/NO3- ratio and the urease activity were increased in the presence of strains TJ6+X43. The combined strains reduced the diversity of bacterial communities, but increased the relative abundances of key strains such as Gemmatimonas, Ramlibacter, Sporacetigenium, Pseudomonas, Microvirga, and Nitrospira in the wheat rhizosphere soil. In addition, the contents of glutamate, glutathione, L-ribulose, arginine, nitrite, spermine, isocitrate, and D-xylulose were also increased. More importantly, glutamate metabolism was roused to induce rhizosphere metabolites and functional bacterial communities to synergistically inactivate Cd. The results showed that inoculation with heavy metal-immobilizing bacteria can result in the activation of key functional bacteria and the regulation of metabolite production in wheat rhizosphere soil to immobilize heavy metals, which has broad potential in the bioremediation of wheat fields and ensuring food security.

Urease-producing bacteria combined with pig manure biochar immobilize Cd and inhibit the absorption of Cd in lettuce (Lactuca sativa L.).

The synergistic remediation of heavy metal-contaminated soil by functional strains and biochar has been widely studied. However, the mechanisms by which urease-producing bacteria combine with pig manure biochar (PMB) to immobilize Cd and inhibit Cd absorption in vegetables are still unclear. In our study, the effects and mechanisms of PMB combined with the urease-producing bacterium TJ6 (TJ6 + PMB) on Cd adsorption were explored. The effects of TJ6 + PMB on the Cd content and pH of the leachate were also studied through a 56-day soil leaching experiment. Moreover, the effects of the complexes on Cd absorption and microbial mechanisms in lettuce were explored through pot experiments. The results showed that PMB provided strain TJ6 with a greater ability to adsorb Cd, inducing the generation of CdS and CdCO3, and thereby reducing the Cd content (71.1%) and increasing the pH and urease activity in the culture medium. TJ6 + PMB improved lettuce dry weight and reduced Cd absorption. These positive effects were likely due to (1) TJ6 + PMB increased the organic matter and NH4+ contents, (2) TJ6 + PMB transformed available Cd into residual Cd and decreased the Cd content in the leachate, and (3) TJ6 + PMB altered the structure of the rhizosphere bacterial and fungal communities in lettuce, increasing the relative abundances of Stachybotrys, Agrocybe, Gaiellales, and Gemmatimonas. These genera can promote plant growth, decompose organic matter, and release phosphorus. Interestingly, the fungal communities were more sensitive to the addition of TJ6 and PMB, which play important roles in the decomposition of organic matter and immobilization of Cd. In conclusion, this study revealed the mechanism by which urease-producing bacteria combined with pig manure biochar immobilize Cd and provided a theoretical basis for safe pig manure return to Cd-polluted farmland. This study also provides technical approaches and bacterial resources for the remediation of heavy metal-contaminated soil.

Urease-producing bacteria with plant growth-promoting ability that may tolerate and remove cadmium from aqueous solution

Urease-producing bacteria (UPB) are widely present in soil and play an important role in soil ecosystems. In this study, 65 UPB strains were isolated from cadmium (Cd)-polluted soil around a lead-zinc mine in Yunnan Province, China. The Cd tolerance, removal of Cd from aqueous solution, production of indoleacetic acid (IAA) and plant growth-promoting effects of these materials were investigated. The results indicate that among the 65 UPB strains, four strains with IAA-producing ability were screened and identified as Bacillus thuringiensis W6-11, B. cereus C7-4, Serratia marcescens W11-10, and S. marcescens C5-6. Among the four strains, B. cereus C7-4 had the highest Cd tolerance, median effect concentration (EC50) of 59.94 mg/L. Under Cd 5 mg/L, S. marcescens C5-6 had the highest Cd removal from aqueous solution, up to 69.83%. Under Cd 25 mg/kg, inoculation with B. cereus C7-4 significantly promoted maize growth in a sand pot by increasing the root volume, root surface area, and number of root branches by 22%, 29%, and 20%, respectively, and plant height and biomass by 16% and 36%, respectively, and significantly increasing Cd uptake in the maize roots. Therefore, UPB is a potential resource for enhancing plant adaptability to Cd stress in plants with Cd-polluted habitats.

Microbial communities, antibiotic resistance genes, and virulence factors in urinary infectious stone-associated urinary tract infections.

Urinary infectious stones are challenging due to bacterial involvement, necessitating a comprehensive understanding of these conditions. Antibiotic-resistant urease-producing bacteria further complicate clinical management. In this study, analysis of urine and stone samples from urinary tract infection (UTI) patients revealed microbial shifts, gene enrichment in stones, and metabolic pathway disparities; antibiotic resistance gene trends were phylum-specific, urease-producing bacteria are at risk of acquiring AMR carried by Enterobacteriaceae under antibiotic, emphasizing potential AMR dissemination between them; Correlations of key pathogenic species in kidney stone and urine microbial communities highlight the need for targeted therapeutic strategies to manage complexities in UTIs; Stones and urine contain a variety of deleterious genes even before antibiotic use, and piperacillin/tazobactam better reduced the abundance of antibiotic resistance genes in stones and urine. The presence of diverse antibiotic resistance and virulence genes underscores challenges in clinical management and emphasizes the need for effective treatment strategies to mitigate risks associated with UTIs and urinary infectious stone formation. Ongoing research is vital for advancing knowledge and developing innovative approaches to address these urological conditions.

Extraction of high activity bacterial urease and its application to biomineralization of soil

Biomineralization based on bacterial enzyme induced carbonate precipitation (BEICP) process is a promising alternative to cement-based ground treatment technology. The bacterial urease used in BEICP process is usually ultrasonic extracted from urease-producing bacteria. To efficiently extract urease with relatively higher activity from bacterial cells, the ultrasonic extraction parameters of urease were optimized in this study. Next, a series of bacterial urease extraction tests and sand column treatment tests were conducted to investigate the effects of vibration amplitude, upper temperature limit, and cooling method on the urease extraction process and biomineralization of sand. The results show that the upper temperature limit is an important factor affecting the extraction efficiency and the activity of the extracted urease solution, and the optimum upper temperature limit is 50 °C. The results indicate that increasing vibration amplitude could improve the extraction efficiency, but it hardly affects the urease activity (UA) under the optimal temperature. Continuous cooling could effectively simplify the operation and further improve the efficiency of urease extraction. Under the same urease activity of biotreatment solution, there is no marked difference in calcium carbonate content (CCC) and unconfined compressive strength of biomineralized sand columns prepared by urease solution extracted with different vibration amplitudes and upper temperature limits. The results of this study could provide a reference for application of BEICP technology of urease extraction to large-scale soil treatment.

A biotechnological approach for suspended solids removal in biogas slurry via microbially induced calcite precipitation (MICP)

This study investigated the application of the microbially induced calcite precipitation (MICP) technique for removing suspended solids from biogas slurry. A series of laboratory tests on suspended solids content and colority determination was conducted to evaluate the feasibility of this technique and the removal performance of suspended solids. Combined with tests on residual calcium ions concentration and micro scale, the effects of crucial factors (including urease activity and CaCl2-Urea content) and the mechanisms of suspended solids removal were explored. The results unequivocally demonstrated the effectiveness of the MICP technique in removing suspended solids, achieving optimum removal efficiencies of 91.67 ± 1.68% for suspended solids and 96.50% for colority. The introduction of additional urease-producing bacteria via centrifugation-extraction increased the urease activity of bacterial solution and further enhanced the degree of MICP reaction, but undesirably led to a slight reduction in the removal efficiencies of suspended solids and colority due to the presence of bacteria themselves as suspended solids. Appropriately increasing the CaCl2-Urea content could offer a more adequate material supply to prolong the duration of the MICP process, significantly enhancing the removal efficiency. Nevertheless, the high salinity environment associated with excessive CaCl2-Urea addition (2.0 mol/L) would impair bacteria survival and impede the MICP process, negatively affecting suspended solids removal. The SEM-EDS analysis indicated that in the MICP process, suspended solids were tightly encapsulated by calcium carbonate (mainly calcite) to form strong immobilization aiding their gravity-driven removal. Due to the richness of organic components, they could be considered for reuse as soil amendments and fertilizers. This research provides an innovative insight into the removal of suspended solids from biogas slurry using a biotechnological approach. The MICP technique holds promise for practical applications due to its effectiveness and workability.

AN EXPERIMENTAL STUDY ON STABILIZING COHESIVE SOIL USING MICROBIALLY INDUCED CALCIUM CARBONATE PRECIPITATION

Bio-cementation is an environmentally friendly procedure grounded on microbial induced carbonate precipitation mechanism, occurring in environments abundant in calcium. In the effort to bolster soil stability, traditional urea is combined with bacteria to enhance the mechanical properties of soil. The research delves into the microbial mechanisms involved in microbially induced calcite precipitation, highlighting the role of urease-producing bacteria in facilitating calcium carbonate precipitation within the soil structure. This also entails pivotal laboratory and field experiments, evaluating the efficacy of microbially induced calcium carbonate in improving soil engineering characteristics, such as strength, permeability, and durability. Furthermore, this process can be employed across various soil types, offering adaptability in geotechnical applications. Additionally, we investigate the environmental consequences and sustainability aspects by underscoring its potential as an eco-friendly substitute for soil enhancement. Nonetheless, challenges such as optimizing bacterial activity, regulating the precipitation process, and ensuring even distribution of calcium carbonate within the soil necessitate further exploration. Based on the envisioned review, it contributes to the comprehension of MICP as a promising method for soil stabilization, providing insights for researchers, practitioners, and policymakers keen on sustainable and inventive approaches to geotechnical engineering. Key Words: Bio-geotechnical engineering, soil stabilization, Microbially induced calcium carbonate Precipitation, Soil improvement.

Etiology, pathogenesis, diagnosis and treatment of encrusted cystitis and pyelitis: Review of the problem from a historical perspective

Introduction: Encrusted cystitis and pyelitis share many similarities regarding etiology, pathogenesis, diagnosis and treatment. These processes usually occur on previously injured urological tissue with the participation of an infection by urease-producing bacteria. At present Corynebacterium urealyticum, a highly antibiotic-resistant bacteria, appears to be the pathogen most often involved in these processes. In this review we analyze the history of these diseases with special emphasis on the scientific advances of the last century. We also review the role of urease and bacterial infection as well as a brief update on the epidemiological, histopathological, diagnostic and therapeutic aspects. Relevance: The importance and severity of these pathologies that are frequently underdiagnosed and difficult to treat are stressed. Conclusions: The clinical history, exploratory and analytical data, which highlight alkaline urine, sometimes with an ammoniacal odor, pyuria, hematuria and the presence of magnesium ammonium phosphate crystals, should alert the urologist to the existence of an encrusting uropathy. Simple radiology, ultrasound, computed tomography and endoscopic visualization of the lesions confirm the diagnosis. Treatment generally requires surgery, use of antibiotics, urinary acidifiers and bacterial urease inhibitors. Keywords: cystitis, pyelitis, encrustations, infection

Hyperammonaemia in cats

Ammonia is an important nitrogen source required for amino acid, protein and nucleic acid synthesis. In addition, it plays an essential role in the kidney's maintenance of acid–base balance. However, high concentrations of ammonia are cytotoxic and clinical signs primarily reflect neurotoxicity. The body detoxifies ammonia through the urea cycle in the liver or by consuming ammonia in the conversion of glutamate to glutamine in the liver, brain and muscle tissue. The most common cause of hyperammonaemia in cats is congenital portosystemic shunting. Additional causes include cobalamin or arginine deficiency, disruption of the urea cycle by congenital enzyme deficiencies or acute liver failure, excessive muscle activity, infections with urease-producing bacteria, kidney disease and multiple acquired portosystemic shunts.

Urease-producing bacteria enhance the adsorption of Cd on organo-Fe hydroxide coprecipitates

Microorganisms, organic carbon, and iron oxides are important active components in soil that control the availability of heavy metals. In the extensive cultivation areas based on wheat–maize rotation, returning corn straw to the field increases the content of dissolved organic carbon (DOC) in the soil, affecting heavy metal adsorption by iron oxides and thereby threatening the safety of wheat. However, the effects and underlying mechanisms of maize straw-derived DOC on Cd adsorption by ferrihydrite (Fh) are unclear, and the effects of functional strains on Cd adsorption by organo-Fe hydroxide coprecipitates (OFCs) need further study. The effect of DOC on the adsorption of Cd by Fh was studied through batch solution adsorption experiments. Moreover, the mechanisms underlying the synergistic adsorption of Cd by the urease-producing bacterium Enterobacter sp. TJ6 and OFC were studied in adsorption experiments via scanning electron microscopy and X-ray photoelectron spectroscopy. The results showed that DOC inhibited the adsorption of Cd by OFC, while strain TJ6 enhanced the adsorption of Cd by OFC. Fe-OH and Fe-O bonds on the surface of Fh were important Cd adsorption sites. DOC affected the adsorption of Cd by Fe-OH and Fe-O, thereby inhibiting the adsorption of Cd by OFC. DOC also served as a reducing agent, reducing Fe2O3 on the surface of OFC to FeO and thus inhibiting OFC adsorption of Cd. The mechanisms by which strain TJ6 enhanced Cd adsorption by OFC included the following: 1) strain TJ6 utilized its own oxidation ability to oxidize FeO on the surface of OFC to Fe2O3, promoting the secondary precipitation of Cd during the redox process and enhancing the Cd adsorption capacity of OFC; and 2) strain TJ6 immobilized Cd2+ through ion exchange between Cd2+ and H+ in surface amino groups. In conclusion, this study has revealed the mechanism by which urease-producing bacteria regulate the adsorption of Cd by OFC and provides a theoretical basis for safe straw return to Cd-polluted farmland. This study also provides technical approaches and bacterial resources for the remediation of heavy metal-contaminated soil under straw return.

Isolation and Characterization of Indigenous Ureolytic Bacteria from Mindanao, Philippines: Prospects for Microbially Induced Carbonate Precipitation (MICP)

Microbially induced carbonate precipitation (MICP), a widespread phenomenon in nature, is gaining attention as a low-carbon alternative to ordinary Portland cement (OPC) in geotechnical engineering and the construction industry for sustainable development. In the Philippines, however, very few works have been conducted to isolate and identify indigenous, urease-producing (ureolytic) bacteria suitable for MICP. In this study, we isolated seven, ureolytic and potentially useful bacteria for MICP from marine sediments in Iligan City. DNA barcoding using 16s rDNA identified six of them as Pseudomonas stutzeri, Pseudomonas pseudoalcaligenes, Bacillus paralicheniformis, Bacillus altitudinis, Bacillus aryabhattai, and Stutzerimonas stutzeri but the seventh was not identified since it was a bacterial consortium. Bio-cementation assay experiments showed negligible precipitation in the control (without bacteria) at pH 7, 8, and 9. However, precipitates were formed in all seven bacterial isolates, especially between pH 7 and 8 (0.7–4 g). Among the six identified bacterial species, more extensive precipitation (2.3–4 g) and higher final pH were observed in S. stutzeri, and B. aryabhattai, which indicate better urease production and decomposition, higher CO2 generation, and more favorable CaCO3 formation. Characterization of the precipitates by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and attenuated total reflectance Fourier transform spectroscopy (ATR-FTIR) confirmed the formation of three carbonate minerals: calcite, aragonite, and vaterite. Based on these results, all six identified indigenous, ureolytic bacterial species from Iligan City are suitable for MICP provided that the pH is controlled between 7 and 8. To the best of our knowledge, this is the first report of the urease-producing ability and potential for MICP of P. stutzeri, P. pseudoalcaligenes, S. stutzeri, and B. aryabhattai.

Inhibition of urease-mediated ammonia production by 2-octynohydroxamic acid in hepatic encephalopathy

Hepatic encephalopathy is a neuropsychiatric complication of liver disease which is partly associated with elevated ammonemia. Urea hydrolysis by urease-producing bacteria in the colon is often mentioned as one of the main routes of ammonia production in the body, yet research on treatments targeting bacterial ureases in hepatic encephalopathy is limited. Herein we report a hydroxamate-based urease inhibitor, 2-octynohydroxamic acid, exhibiting improved in vitro potency compared to hydroxamic acids that were previously investigated for hepatic encephalopathy. 2-octynohydroxamic acid shows low cytotoxic and mutagenic potential within a micromolar concentration range as well as reduces ammonemia in rodent models of liver disease. Furthermore, 2-octynohydroxamic acid treatment decreases cerebellar glutamine, a product of ammonia metabolism, in male bile duct ligated rats. A prototype colonic formulation enables reduced systemic exposure to 2-octynohydroxamic acid in male dogs. Overall, this work suggests that urease inhibitors delivered to the colon by means of colonic formulations represent a prospective approach for the treatment of hepatic encephalopathy.