Ureolytic Activity Research Articles

Genome-wide comparative analysis of clinical and environmental strains of the opportunistic pathogen Paracoccus yeei (Alphaproteobacteria)

IntroductionParacoccus yeei is the first species in the genus Paracoccus to be implicated in opportunistic infections in humans. As a result, P. yeei strains provide a valuable model for exploring how bacteria shift from a saprophytic to a pathogenic lifestyle, as well as for investigating the role of horizontally transferred DNA in this transition. In order to gain deeper insights into the unique characteristics of this bacterium and the molecular mechanisms underlying its opportunistic behavior, a comparative physiological and genomic analysis of P. yeei strains was performed.ResultsComplete genomic sequences of 7 P. yeei isolates (both clinical and environmental) were obtained and analyzed. All genomes have a multipartite structure comprising numerous extrachromosomal replicons (59 different ECRs in total), including large chromids of the DnaA-like and RepB families. Within the mobile part of the P. yeei genomes (ECRs and transposable elements, TEs), a novel non-autonomous MITE-type element was identified. Detailed genus-wide comparative genomic analysis permitted the identification of P. yeei-specific genes, including several putative virulence determinants. One of these, the URE gene cluster, determines the ureolytic activity of P. yeei strains—a unique feature among Paracoccus spp. This activity is induced by the inclusion of urea in the growth medium and is dependent on the presence of an intact nikR regulatory gene, which presumably regulates expression of nickel (urease cofactor) transporter genes.DiscussionThis in-depth comparative analysis provides a detailed insight into the structure, composition and properties of P. yeei genomes. Several predicted virulence determinants (including URE gene clusters) were identified within ECRs, indicating an important role for the flexible genome in determining the opportunistic properties of this bacterium.

Bacterial activity and cementation pattern in biostimulated MICP-treated sand-bentonite mixtures

The application of microbially induced carbonate precipitation (MICP) in clayey soils has attracted much attention, and many studies used clay as an additive to enhance microbial mineralization efficiency in sandy soils. Within the sand-clay-bacteria-calcite system, the property and content of clay play crucial roles in affecting bacterial growth and calcite formation. More important, bentonite is particularly sensitive to changes in the geochemical environment. In this study, the sand-bentonite mixtures were treated by biostimulated MICP, aiming to provide insights into the behavior of this system. The bacterial activity and cementation pattern at different bentonite contents were evaluated through a series of tests such as enrichment tests, unconfined compressive strength (UCS) tests, cementation content measurements, mercury intrusion porosimetry (MIP) tests, scanning electron microscopy (SEM) observations, and energy dispersive X-ray spectroscopy (EDS) analyses. The findings showed that the bentonite presence promoted the enrichment of indigenous ureolytic bacteria, with lower bentonite levels enhancing ureolytic activity. Macroscopic and microscopic characterization indicated that the bentonite-coating sand structure was more conducive to the formation of large-sized calcite crystals capable of cementing soil particles compared to sand-supported and bentonite-supported structures. Additionally, excessive calcium ions (Ca2+) concentrations in the cementitious solution would lead to predominant calcite deposition on soil particle surfaces, contributing minimally to strength improvement.

Molecular and geochemical basis of microbially induced carbonate precipitation for treating acid mine drainage: The case of a novel Sporosarcina genomospecies from mine tailings

Microbially induced carbonate precipitation (MICP) immobilizes toxic metals and reduces their bioavailability in aqueous systems. However, its application in the treatment of acid mine drainage (AMD) is poorly understood. In this study, the genomes of Sporosarcina sp. UB5 and UB10 were sequenced. Urease, carbonic anhydrases, and metal resistance genes were identified and enzymatic assays were performed for their validation. The geochemical mechanism of precipitation in AMD was elucidated through geo-mineralogical analysis. Sporosarcina sp. UB5 was shown to be a new genomospecies, with an average nucleotide identity < 95 % (ANI) and DNA-DNA hybridization < 70 % (DDH) whereas UB10 is close to S. pasteurii. UB5 contained two urease operons, whereas only one was identified in UB10. The ureolytic activities of UB5 and UB10 were 122.67 ± 15.74 and 131.70 ± 14.35 mM NH4+ min−1, respectively. Both strains feature several carbonic anhydrases of the α, β, or γ families, which catalyzed the precipitation of CaCO3. Only Sporosarcina sp. UB5 was able to immobilize metals and neutralize AMD. Geo-mineralogical analyses revealed that UB5 directly immobilized Fe (1–23 %), Mn (0.65–1.33 %) and Zn (0.8–3 %) in AMD via MICP and indirectly through adsorption to calcite and binding to bacterial cell walls. The MICP-treated AMD exhibited high removal rates (>67 %) for Ag, Al, As, Ca, Cd, Co, Cu, Fe, Mn, Pb, and Zn, and a removal rate of 15 % for Mg. This study provides new insights into the MICP process and its applications to AMD treatment using autochthonous strains.

Synergistic inhibition of ureolytic activity and growth of Klebsiella pneumoniae in vitro suggests cobinding of fluoride and acetohydroxamic acid at the urease active site and provides a novel strategy to combat ureolytic bacteria

The ability of ureolytic bacteria to break down stable urea to alkaline ammonia leads to several environmental and health challenges. Ureolytic bacteria such as Helicobacter pylori, Klebsiella pneumoniae, and Proteus mirabilis can become pathogenic and cause persistent infections that can be difficult to treat. Inhibiting urease activity can reduce the growth and pathogenicity of ureolytic bacteria. In the present in vitro study, we investigated the synergistic effects of tannic acid (TA) and the urease inhibitors fluoride (F−) and acetohydroxamic acid (AHA). The concentration of AHA needed for efficient inhibition of the ureolytic activity of K. pneumoniae can be significantly reduced if AHA is coapplied with tannic acid and sodium fluoride (NaF). Thus, only 1.20 μmol l−1 AHA in combination with 0.30 mmol l−1 tannic acid and 0.60 mmol l−1 NaF delayed the onset of ureolytic pH increase by 95.8 % and increased the growth lag phase by 124.3 % relative to untreated K. pneumoniae. At these concentrations, without AHA, TA and NaF increased the onset of the ureolytic pH change by only 37.0 % and the growth lag phase by 52.5 %. The strong inhibition obtained with low concentrations of AHA in triple-compound treatments suggests cobinding of F− and AHA at the urease active site and could reduce the side effects of AHA when it is employed as a drug against e.g. urinary tract infections (UTIs) and blocked catheters. This study reports the basis for a promising novel therapeutic strategy to combat infections caused by ureolytic bacteria and the formation of urinary tract stones and crystalline biofilms on catheters.

Coupled multiphysical model for investigation of influence factors in the application of microbially induced calcite precipitation

The study presents a comprehensive coupled thermo-bio-chemo-hydraulic (T-BCH) modeling framework for stabilizing soils using microbially induced calcite precipitation (MICP). The numerical model considers relevant multiphysics involved in MICP, such as bacterial ureolytic activities, biochemical reactions, multiphase and multicomponent transport, and alteration of the porosity and permeability. The model incorporates multiphysical coupling effects through well-established constitutive relations that connect parameters and variables from different physical fields. It was implemented in the open-source finite element code OpenGeoSys (OGS), and a semi-staggered solution strategy was designed to solve the couplings, allowing for flexible model settings. Therefore, the developed model can be easily adapted to simulate MICP applications in different scenarios. The numerical model was employed to analyze the effect of various factors, including temperature, injection strategies, and application scales. Besides, a T-BCH modeling study was conducted on the laboratory-scale domain to analyze the effects of temperature on urease activity and precipitated calcium carbonate. To understand the scale dependency of MICP treatment, a large-scale heterogeneous domain was subjected to variable biochemical injection strategies. The simulations conducted at the field-scale guided the selection of an injection strategy to achieve the desired type and amount of precipitation. Additionally, the study emphasized the potential of numerical models as reliable tools for optimizing future developments in field-scale MICP treatment. The present study demonstrates the potential of this numerical framework for designing and optimizing the MICP applications in laboratory-, prototype-, and field-scale scenarios.

Recent Advances in Anti-Urease Activity of Schiff Bases and their Metal Complexes

The urease enzyme, found in plants, fungi and bacteria, plays a crucial role in catalyzing the hydrolysis of urea, a process integral to microbial metabolism. Its ureolytic activities have garnered significant attention for their impact on agriculture and the health of living organisms. Notably, urease activity in the human stomach, urinary tract and animal cells can lead to pathogenic outcomes. Schiff bases, characterized by their carbonyl-type imine or azomethine linkage, are recognized for their diverse biological effects, including anti-urease activity. Additionally, the metal complexes derived from the Schiff bases demonstrate controlled urease inhibition activity, influenced by factors such as the type of metal, its oxidation state and the coordination environment. This inhibition occurs through the interaction of the Schiff base ligand with the nickel containing active site of urease or the protein sphere surrounding the metal, disrupting the ureolytic mechanism. In this review, the utilization of Schiff bases and their metal complexes in urease inhibition is highlighted as explored by various research groups.

Differential expression of urease genes and ureolytic activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa isolates in different nutritional conditions.

Uropathogens have adaptation strategies to survive in the host urinary tract by efficiently utilizing and tolerating the urinary metabolites. Many uropathogens harbour the enzyme urease for the breakdown of urea and the enzymatic breakdown of urea increases the pH and facilitate the struvite crystallization. In this study, the differential urease activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa strains was investigated under different nutritional conditions. The experiments included measurement of growth, pH, urease activity, NH4-N generation and urease gene (ureC) expression among the bacterial strains under different conditions. Further, the implications of urea breakdown on the struvite crystallization in vitro and biofilm formation were also assessed. The study included urease positive isolates and for comparison urease negative isolates were included. Compared to the urease negative strains the urease positive strains formed higher biofilms and motility. The urease positive P. aeruginosa showed significantly higher (p < 0.01) pH and urease activity (A557-A630) compared to E. coli under experimental conditions. Further, supplementation of glucose to the growth media significantly increased the urease activity in P. aeruginosa and in contrast, it was significantly lower in E. coli. The expression profile of urease gene (ureC) was significantly higher (p < 0.001) in P. aeruginosa compared to E. coli and was consistent with the biochemical results of the urease activity under the nutritional conditions. The differential urease activity under two nutritional conditions influenced the biogenic struvite crystallization. It correlated with the urease activity showing higher crystallization rate in P. aeruginosa compared to E. coli. The results highlight the differential urease activity in two common uropathogens under different nutritional conditions that may have significant role on the regulation of virulence, pathogenicity and in the kidney stone disease.

Screening of bacteria in Yarık Sinkhole, Antalya, Turkey for carbonate dissolution, biomineralization and biotechnological potentials

Abiotic and biotic factors, especially microorganisms, play a role in the development of cave formations and the existence of unique characteristics of each cave. Due to the ecological conditions that characterize the cave environments, highly specialized microorganisms that are the main source of diverse bioactive compounds, inhabit these environments. The aim of this study is to determine the role and biotechnological potential of the bacteria isolated from Yarık Sinkhole located in Antalya (Turkey) by screening their ability to induce the CaCO3 precipitation, to hydrolyze urea, to induce calcite dissolution, and screening their possession of NRPS/PKS gene clusters. The most prevalent phylum is the Bacillota (synonym Firmicutes) (75.7 %), while the dominant species is Bacillus pumilus (33 %). All the isolates showed crystal formation on B4 agar medium, and the Energy dispersive X-Ray spectroscopy (EDS) analyses showed that the crystals are predominately composed of calcium, carbon and oxygen. Ninety-six (96 %) of our isolates have negative ureolytic activity. According to this result and having the ability to induce the CaCO3 precipitation, bac­teria in this environment use other biosynthesis pathways than urea hydrolysis. MgCO3 and CaCO3 were dissolved by 61 % and 59 % of the isolates, respectively. In addition, 5.9 % and 53.7 % of the isolates showed the possession of PKS and NRPS genes, respectively. This result reveals that our isolates have high in­dustrial and biotechnological potential. They may constitute good candidates for further biotechnological applications such as construction of bio-concretes, bioremediation, soil fertility, and production of biologically active secondary metabolites.

Structural and Functional Analysis of Urease Accessory Protein E from Vancomycin-Resistance Staphylococcus aureus MU50 Strain.

An increasing prevalence of biofilm forming strains by vancomycinresistance Staphylococcus aureus (VRSA) is one of the most important causes of antimicrobial resistance. VRSA possesses various regulatory factors to form and sustain biofilm in biotic or abiotic conditions. Among them, ureolytic activity is an important factor in the stabilization of biofilms by neutralizing the acidic environment. Various urease accessory proteins are required to activate the urease enzyme inside the biofilm. To optimize the cloning, expression and purification of urease accessory protein E from VRSA for determination of the secondary structure, and functional characterization by using Berthelot's method. BAB58453.1 gene (which encodes possible urease accessory protein E), having 38% similarity to Bacillus pasteurii UreE protein, was cloned, expressed, and purified by single-step affinity chromatography for performing secondary structural studies using circular dichroism spectroscopy, and functional analysis using Berthelot's and crystal violet assay. Structure elucidation using NMR and circular dichroism spectroscopy techniques revealed that UreE protein has a partially foldedα-helical structure. Using Berthelot's method, it was identified that the purified UreE protein has enhanced urease enzyme activity, in comparison to the control. From the results of Berthelot's and crystal violet assays, it was deduced that the selected gene (UreE protein) plays a key role in enhancing urease enzyme activity and contributes to biofilm stability. Structural studies on VRSA urease accessory proteins could aid in the identification of new drug targets or the development of effective antibiofilm strategies (in combination with other drug targets) against infections caused by biofilm-producing strains.

Unlocking the Potential of Microbially Induced Calcium Carbonate Precipitation (MICP) for Hydrological Applications: A Review of Opportunities, Challenges, and Environmental Considerations

Microbially induced calcium carbonate precipitation (MICP) is an innovative biocementation technique that facilitates the formation of calcium carbonate within a pore network. Initially gaining prominence in the field of geotechnical engineering, MICP has attracted significant attention since its inception (the last three decades) and expanded its reach across various engineering disciplines. Examples include rock mechanics, geology and the oil and gas industry fields through the generation of rock-like specimens, and plugging of fractures, in civil and architectural engineering and material science for concrete repair, protection, and for self-healing of building materials, and in environmental engineering for the study of biomimetic materials. In response to this burgeoning interest, the current paper aims to present a comprehensive review of the main biochemical mechanisms underlying MICP (bacterial ureolytic activity, reactions duration and settling times, and chemical solution properties), their direct relevance to altering hydraulic and mechanical properties, both at the microscale and macroscale responses, and the precipitation mechanisms, particularly in relation to water resources and hydrology applications. Four main categories of relevant applications are identified, namely, the groundwater and soil remediation, the applications related to the generation of a low hydraulic conductivity barrier, those related to gaining cohesion, and the applications related to fluid flow studies in artificially generated porous media. Moreover, this comprehensive review not only aims to identify the existing applications of MICP within hydrological fields but also strives to propose novel and promising applications that can further expand its utility in this domain. Along with the investigation of the potential of MICP to revolutionize water resources and hydrology, it is imperative to delve deeper into its environmental implications to ensure sustainable and ecologically responsible implementation.

Growing bio-tiles using microbially induced calcium carbonate precipitation

Using the biomimetic process known as microbially induced calcium carbonate precipitation (MICP), the growth of bio-tiles was investigated as an alternative to conventionally fired ceramic tiles which require operating temperatures above 1000 °C, therefore adding to global carbon emissions. The ureolytic activity of Sporosarcina pasteurii was controlled by centrifuging and dilution with fresh yeast extract media. The bio-tiles were grown using a novel submersion method in which custom moulds were placed in exact positions within the bio-reactor and each was mixed individually from beneath. Five parameters were optimised to achieve bio-tiles (dimensions of 100 × 100 × 10 mm) of breaking strength comparable to conventional tiles of equivalent thickness. By optimising ureolytic activity (4.0 mmol/L·min), the cementation solution concentration (0.3 M), the particle size distribution (D10 = 312 μm; D50 = 469 μm), the volume of cementation solution, as well as the addition of supplemental magnesium (0.3 M), bio-tiles with a breaking strength 637 N ± 60 N and a modulus of rupture of 13.0 N/mm2 ± 2.3 N were produced. These parameters exceed the conventional standards of breaking strength and modulus of rupture of 600 N and 8 N/mm2, respectively, the standards set for tiles with a water absorption above 10 %. This is also the first time that an optimum CaCO3 precipitation rate constant has been identified (0.11–0.18 day−1) for producing bio-tiles that meet the strength properties of conventional extruded ceramic tiles. The tile manufacturing technique described in this study is easy to operate and scale since multiple bio-tiles can be produced in larger cementation tanks. This natural tile making process also benefits the environment by operating at room temperature.

Improving the spatial control of soil biocementation using indigenous microorganisms: Column experiments and reactive transport modeling

Microbially-Induced Calcite Precipitation (MICP), or biocementation, is a biomediated soil improvement process that uses microbial ureolytic activity to enable the precipitation of CaCO3 on soil particle surfaces and contacts. As the technology advances towards practical adoption, approaches that can modulate the spatial uniformity of biocementation and maximize treatment extent will be critical towards reducing implementation costs and impacts. In this study, treatment strategies capable of enriching indigenous ureolytic microorganisms at controlled ureolytic activities and the effects of these techniques on resulting spatial distributions of MICP were explored using centimeter- and meter-scale soil column experiments and reactive transport simulations. In column experiments, differences in treatment solution supplied yeast extract concentrations were shown to reliably control the enrichment of indigenous ureolytic microorganisms and achieve a wide range of ureolytic activities. Reactive transport simulations further demonstrated that reductions in stimulated ureolytic rates could enable more uniform improvement and increases in the extent of improvement with reduced sensitivity to changes in solution injection velocities. A reaction-to-injection duration ratio (RTIDR) parameter was proposed and captured the collective impacts of changes in injection rates and ureolytic reaction rates on reactive transport conditions thereby unifying outcomes from both simulations and experiments. A nonuniformity area (NA) parameter was also introduced to quantitatively characterize differences in biocementation uniformity independent of length scale and CaCO3 magnitudes. Results from this study collectively demonstrate the utility of changes in stimulated ureolytic activities towards controlling the spatial uniformity and extent of biocementation over meter-scale distances.

Effect of Barbituric Acid and Chlortetracycline upon Growth, Ammonia Concentration, and Urease Activity in the Gastrointestinal Tract of Chicks

Experiments were conducted with a total of 38 lots of 15 chicks. Preliminary data from 22 lots indicate that the addition of either barbituric acid (1.28 g/kg) or chlortetracycline (0.1 g/kg) will enhance 4-week gains with diets containing either soybean meal or vitamin-free casein. An experiment with 16 lots fed a crude casein diet showed enhanced growth of 17% with barbituric acid and 25% with chlortetracycline. The combination improved gain 26%. At the time these chicks were killed, they had lowered gastrointestinal ammonia concentrations. Urease activity was also lowered in birds receiving these supplements but activity in the small intestine was variable. The data show that a cyclic urea compound can produce increased growth coincidently with decreased ureolytic activity and ammonia concentration in the gastrointestinal tract.

Virulence Characterization of Coagulase-Negative Staphylococci Isolated from Sexually Active Women with Symptomatic Genital Tract Infection, In Comparison with Staphylococcus aureus Isolated from the Same Cases

This study included 33 coagulase-negative staphylococci (CNS) and 35 Staphylococcus aureus isolated from sexually active females with symptomatic genital tract infection (64 pregnant and 110 non-pregnant). Comparison of phenotypic characteristics showed that the difference is not significant between CNS and S. aureus isolates for hemolytic activity (63.6% and 54.2%, respectively); lipolytic activity (87.8% and 88.5%, respectively); protease production (18.1% and 31.4%, respectively). and biofilm formation ( 96.9% and 94.2%, respectively). Whereas the difference is significant (P≤ 0.05) for urease production (18.1% and 42.8%, respectively). With the exception of lipolytic activity and biofilm formation, co-expression of other factors showed that there was an opposite expression of hemolytic and proteolytic activities of both CNS and S. aureus isolates. For CNS only 3/33 (9%) of the isolates were hemolytic and preoteolytic while for S. aureus only 2/35 (5.7%) isolates had this characteristics. Also for S. aureus isolates, ureolytic activity was more correlated with hemolytic (20%) and proteolytic (11.4%) activities than in CNS (6.0% and 3.0%, respectively). We concluded that, for this study included factors, the virulence of CNS isolated from females' genital tract infection is comparable to that of the potential females' genital tract pathogen, S. aureus. So that, CNS can be opportunistic pathogens in these cases rather than mere contaminants.

Suitable yeast extract concentration for the production of self-healing mortar with expanded clay as bacterial carrier

In microbial induced calcium carbonate precipitation (MICP) system, yeast extract (YE) is needed for spores germination. The aim of this research is to evaluate the minimum amount of YE in mortar that allows spores of Bacillus sphaericus to germinate with limited negative effect on mortar properties. Two YE concentrations of 2 and 5 g/l were tested and compared to a reference without YE. To protect the bacteria in the mortar matrix, spores or cells were encapsulated into porous expanded clay. The ureolytic activity of bacteria with YE variation, the mechanical properties and the healing ability of mortar were assessed. The results show that a YE concentration of 2 g/l provided acceptable mortar properties, while it was sufficient for spores to germinate and provide a satisfactory healing ability to resulting mortar. When vegetative cells are used as a healing agent, it is best to omit yeast extract from the mortar mixture.

Mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation in the presence of seawater ions and varying soil materials

Microbially-induced calcium carbonate precipitation (MICP) is a bio-cementation process that can improve the engineering properties of granular soils through the precipitation of calcium carbonate (CaCO3) minerals on soil particle surfaces and contacts. The technology has advanced rapidly as an environmentally conscious soil improvement method, however, our understanding of the effect of changes in field-representative environmental conditions on the physical and chemical properties of resulting precipitates has remained limited. An improved understanding of the effect of subsurface geochemical and soil conditions on process reaction kinetics and the morphology and mineralogy of bio-cementation may be critical towards enabling successful field-scale deployment of the technology and improving our understanding of the long-term chemical permanence of bio-cemented soils in different environments. In this study, thirty-five batch experiments were performed to specifically investigate the influence of seawater ions and varying soil materials on the mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation. During experiments, differences in reaction kinetics were quantified to identify conditions inhibiting CaCO3 precipitation and ureolysis. Following experiments, scanning electron microscopy, x-ray diffraction, and chemical composition analyses were employed to quantify differences in mineralogical compositions and material morphology. Ions present in seawater and variations in soil materials were shown to significantly influence ureolytic activity and precipitate mineralogy and morphology, however, calcite remained the predominant CaCO3 polymorph in all experiments with relative percentages exceeding 80% by mass in all precipitates.

Immobilization of heavy metals by microbially induced carbonate precipitation using hydrocarbon-degrading ureolytic bacteria

Crude oil contamination introduces multiple threats to human health and the environment, most of which are from toxic heavy metals. Heavy metals cause significant threats because of their persistence, toxicity, and bio-accumulation. Biomineralization, performed through many microbial processes, can lead to the immobilization of heavy metals in formed minerals. The potential of the microbially carbonate-induced precipitation (MICP) in removal by biomineralization of several heavy metals was investigated. A collection of diverse 11 bacterial strains exhibited ureolytic activity and tolerance to heavy metals when growing in Luria-Bertani (LB) and urea medium. Determination of the minimum inhibitory concentrations (MIC) revealed that heavy metal toxicity was arranged as Cd > Ni > Cr > Cu > Zn. Three hydrocarbon-degrading bacterial strains (two of Pseudomonas aeruginosa and one of Providencia rettgeri) exhibited the highest tolerance (MIC > 5 mM) to Cu, Cr, Zn, and Ni, whereas Cd exerted significantly higher toxicity with MIC <1 mM. At all MICP conditions, different proportions of calcium carbonate (calcite) and calcium phosphate (brushite) were formed. Pseudomonas aeruginosa strains (QZ5 and QZ9) exhibited the highest removal efficiency of Cr (100%), whereas Providencia rettgeri strain (QZ2) showed 100% removal of Zn. Heavy metal complexes were found as well. Cd removal was evidenced by the formation of cadmium phosphate induced by Providencia rettgeri bacterial activity. Our study confirmed that hydrocarbon-degrading ureolytic bacteria not only can tolerate heavy metal toxicity but also have the capability to co-precipitate heavy metals. These findings indicate an effective and novel biological approach to bioremediate petroleum hydrocarbons and immobilize multiple heavy metals with mineral formation. This is of high importance for ecological restoration via stabilization of soil and alleviation of heavy metal toxicity.

Start-up and performance of a downflow fluidised bed reactor for biological treatment of yellow wastewater and nutrient recovery

The treatment of yellow water (human urine) in a downflow fluidised bed reactor (DFFBR) was investigated to evaluate biological ureolysis and nutrient recovery. The reactor was operated at 30±4 °C in batch mode, and reaction time = 1 d. The average immobilised biomass (as volatile solids, IVS) in the reactor was 2.5±0.9 g L-1support, and specific ureolytic activity was 121 g Urea-N g-1 IVS d-1. The kinetic parameters were 0.152 mol L-1 (Km) and 8 mol g-1 IVS d-1 (Vmax). The ureolysis efficiency was 93.4% and chemical oxygen demand removal efficiency was 31.2%, while total ammonium nitrogen (NH4+-N) production rate was 7 g L-1 d-1 and phosphate removal reached 26%. Precipitates recovery during biological treatment was 1.72±0.8 g. These results suggest that the treatment of yellow water in a DFFBR is a viable option for partial recovery of N and P.

Biocalcifying Potential of Ureolytic Bacteria Isolated from Soil for Biocementation and Material Crack Repair.

Microbially induced calcium carbonate precipitation (MICP) has been highlighted for its application in civil engineering, and in the environmental and geotechnical fields. Ureolytic activity is one of the most promising bacterial mechanisms in terms of inducing calcium carbonate formation. In this study, four bacterial isolates with high-yield urease production capabilities were obtained from two-step screening using a high-buffered urea medium. The highest urease activity and calcium carbonate formation was observed in Lysinibacillus fusiformis 5.1 with 4.40 × 103 unit/L of urease and 24.15 mg/mL of calcium carbonate, followed by Lysinibacillus xylanilyticus 4.3 with 3.93 × 103 unit/L of urease and 22.85 mg/mL of calcium carbonate. The microstructure of the precipitated crystalline calcium carbonate was observed using scanning electron microscopy. X-ray diffraction analysis confirmed that the main polymorph of the calcium carbonate particle obtained from both isolates was calcite. Examination of the material-crack filling in mortar specimens showed that calcite layers had formed along the crack edges and inside after 10 days, and gradually filled the cracks up to the upper surface. These results showed that these two isolates presented robust characteristics of potential MICP-inducing bacteria for civil engineering and material engineering applications.

Use of recycled concrete aggregates as carriers for self-healing of concrete cracks by bacteria with high urease activity

Microbial induced carbonate precipitation (MICP) has become one of the most attractive strategies to achieve self-healing of concrete cracks in recent decades. In order to provide a moderate space for bacteria in the harsh environment of concrete, the incorporation of protective carriers is a necessity. In this study, the microbial urease activity at different generation of propagation in the selected culture medium was first investigated, followed by exploring the potential of using recycled concrete aggregates (RCAs) as microbial carriers, considering the porous nature of RCAs. The specific urease activity of bacteria at 48 h kept as high as 2.4 × 10−8 mM·min−1·cells−1 even after 5 generations of propagation in the selected culturing medium. RCAs would not result in a loss of ureolytic activity after immobilization and were capable of retaining bacterial viability during concrete mixing. Compared with concrete without any healing agents or with only substrates and calcium source, the one with bio-agents loaded in RCAs completed most of the crack healing in the first week. When the initial crack widths were less than 0.6 mm, the average crack healing ratio and the crack area healing ratio were 71% and 84%, respectively, for microbial self-healing. The depth of crack healing was 17.8 mm as indicated by the microbial precipitates on the crack wall. After microbial self-healing, the compressive strength regain ratio achieved 99.7% while the water tightness regain ratio attained 99.2%, and the cracks were filled with densely packed irregular rhombohedral-shaped crystals consisting of calcite and a small amount of vaterite.