Selective enrichment and production of highly urease active bacteria by non-sterile (open) chemostat culture

Enhanced MICP for Soil Improvement and Heavy Metal Remediation: Insights from Landfill Leachate-Derived Ureolytic Bacterial Consortium

This study investigates the potential of microbial-induced calcium carbonate precipitation (MICP) for soil stabilization and heavy metal immobilization, utilizing landfill leachate-derived ureolytic consortium. Experimental conditions identified yeast extract-based media as most effective for bacterial growth, urease activity, and calcite formation compared to nutrient broth and brown sugar media. Optimal MICP conditions, at pH 8-9 and 30 °C, supported the most efficient biomineralization. The process facilitated the removal of Cd2+ (99.10%) and Ni2+ (78.33%) while producing stable calcite crystals that enhanced soil strength. Thermal analyses (thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)) confirmed the successful production of CaCO3 and its role in improving soil stability. DSC analysis revealed endothermic and exothermic peaks, including a significant exothermic peak at 444 °C, corresponding to the thermal decomposition of CaCO3 into CO2 and CaO, confirming calcite formation. TGA results showed steady weight loss, consistent with the breakdown of CaCO3, supporting the formation of stable carbonates. The MICP treatment significantly increased soil strength, with the highest surface strength observed at 440 psi, correlating with the highest CaCO3 content (18.83%). These findings underscore the effectiveness of MICP in soil stabilization, pollutant removal, and improving geotechnical properties.

Medium optimization and dust suppression performance analysis of microbial-based dust suppressant compound by response surface curve method

At present, microbial dust suppressants based on microbial communities lack necessary systematic analysis of factors affecting dust suppression performance. Therefore, in this study, the response surface curve method was used to optimize the culture conditions for enrichment of urease-producing microorganisms from activated sludge. The results indicated that when urea = 9.67 g L-1, NH4Cl = 5.21 g L-1, and pH = 9.57, the maximum urease activity of urease-producing microbial community (UPMC) was 8.22 mM min-1. The UPMC under optimized culture conditions reached a mineralization rate of 98.8% on the 1st day of mineralization. Ureolysis is one of the biological mechanisms that trigger microbial mineralization with the consequent effect of dust suppression. The analysis of microbial community structure indicated that the urease-producing bacteria Sporosarcina sp. had the highest abundance at the genus level in the microbial-based dust suppressant compound. Jeotgalicoccus sp. plays an important role in improving and maintaining the stability of urease. In addition, the optimal UPMC had low pathogenicity, which is extremely attractive for the safe application of microbial dust suppressants.

Composite biomediated engineering approaches for improving problematic soils: Potentials and opportunities

Several conventional chemical stabilizers are used for soil stabilization, among which cement is widely adopted. However, the high energy consumption and environmental challenges associated with these stabilizers have necessitated the transition toward the adoption/deployment of eco-friendly approaches for soil stabilization. Biomediated techniques are sustainable soil improvement methods adopting less toxic microorganisms, enzymes, or polymers for cementing soil. However, these processes also have several drawbacks, such as slow hardening, environmental impact, high cost, and lack of compatibility with different types of soils. It is hypothesized that these limitations may be overcome by exploring the prospects and opportunities offered by hybrid technological approaches involving the integration of nontraditional stabilizers and microbial-induced biomineralization processes for improving problematic soils. This paper discusses selected previous studies integrating different technologies and their benefits and challenges. The emerging fungi-based bio-mediation techniques and the possibility of forming sustainable fungal-based biocomposites to improve problematic soils are also highlighted.

Application of urease-producing microbial community in seawater to dust suppression in desert

In order to solve the dust problem caused by sandstorms, this paper aims to propose a new method of enriching urease-producing microbial communities in seawater in a non-sterile environment. Besides, the difference of dust suppression performance of enriched microorganisms under different pH conditions was also explored to adapt the dust. The Fourier-transform infrared spectrometry (FTIR) and Scanning electron microscopy (SEM) confirmed the formation of CaCO₃. The X-ray diffraction (XRD) further showed that the crystal forms of CaCO₃ were calcite and vaterite. When urease activity was equivalent, the alkaline environment was conducive to the transformation of CaCO₃ to more stable calcite. The mineralization rate at pH = 10 reached the maximum value on the 7^th day, which was 97.49 ± 1.73%. Moreover, microbial community analysis results showed that the relative abundance of microbial community structure was different under different pH enrichment. Besides, the relative abundance of Sporosarcina, a representative genus of urease-producing microbial community, increased with the increase of pH under culture conditions, which consistent with the mineralization performance results. In addition, the genus level species network diagram also showed that in the microbial community, Sporosarcina was negatively correlated with another urease-producing genus Bacillus, and had a reciprocal relationship with Atopostipes, which means that the urease-producing microbial community was structurally stable. The enrichment of urease-producing microbial communities in seawater will provide empirical support for the large-scale engineering application of MICP technology in preventing and controlling sandstorms in deserts.

Research status and development of microbial induced calcium carbonate mineralization technology

In nature, biomineralization is a common phenomenon, which can be further divided into authigenic and artificially induced mineralization. In recent years, artificially induced mineralization technology has been gradually extended to major engineering fields. Therefore, by elaborating the reaction mechanism and bacteria of mineralization process, and summarized various molecular dynamics equations involved in the mineralization process, including microbial and nutrient transport equations, microbial adsorption equations, growth equations, urea hydrolysis equations, and precipitation equations. Because of the environmental adaptation stage of microorganisms in sandy soil, their reaction rate in sandy soil environment is slower than that in solution environment, the influencing factors are more different, in general, including substrate concentration, temperature, pH, particle size and grouting method. Based on the characteristics of microbial mineralization such as strong cementation ability, fast, efficient, and easy to control, there are good prospects for application in sandy soil curing, building improvement, heavy metal fixation, oil reservoir dissection, and CO₂ capture. Finally, it is discussed and summarized the problems and future development directions on the road of commercialization of microbial induced calcium carbonate precipitation technology from laboratory to field application.

Experimental Study on High-Temperature Damage Repair of Concrete by Soybean Urease Induced Carbonate Precipitation

In this study, the effects of soybean-urease-induced carbonate precipitation on a high-temperature damage repair of concrete were explored. C50 concrete specimens were exposed to high temperatures from 300 to 600 °C, then cooled to an ambient temperature and repaired by two different methods. The influences of the damage temperature and repair methods on surface film thickness, average infrared temperature increase, water absorption, and compressive strength were investigated. Scanning electron microscopy (SEM) images were carried out to further study the mechanism involved. The results revealed that the white sediments on the surface of the repaired specimens were calcium carbonate (CaCO₃) and calcium oxalate (CaC₂O₄). The surface film thickness reached up to 1.94 mm after repair. The average infrared temperature increase in the repaired specimens at different damage temperatures was averagely reduced by about 80% compared with that before the repair. It showed more obvious repair effects at higher temperatures in water absorption and compressive strength tests; the compressive strength of repaired specimens was 194% higher than that before repairs at 600 °C. A negative pressure method was found to be more effective than an immersion method. This study revealed the utilization of SICP on repairing high-temperature damage of concrete is feasible theoretically.

Urease production using corn steep liquor as a low-cost nutrient source by Sporosarcina pasteurii: biocementation and process optimization via artificial intelligence approaches

To commercialize the biocementation through microbial induced carbonate precipitation (MICP), the current study aimed at replacing the costly standard nutrient medium with corn steep liquor (CSL), an inexpensive bio-industrial by-product, on the production of urease enzyme by Sporosarcina pasteurii (PTC 1845). Multiple linear regression (MLR) in linear and quadratic forms, adaptive neuro-fuzzy inference system (ANFIS), and genetic programming (GP) were used for modeling of process based on the experimental data for improving the urease activity (UA). In these models, CSL concentration, urea concentration, nickel supplementation, and incubation time as independent variables and UA as target function were considered. The results of modeling showed that the GP model had the best performance to predict the extent of urease, compared to other ones. The GP model had higher R² as well as lower RSME in comparison with the models derived from ANFIS and MLR. Under the optimum conditions optimized by GP method, the maximum UA value of 3.6 Mm min^-1 was also obtained for 5%v/v CSL concentration, 4.5 g L^-1 urea concentration, 0 μM nickel supplementation, and 60 h incubation time. A good agreement between the outputs of GP model for the optimal UA and experimental result was obtained. Finally, a series of laboratory experiments were undertaken to evaluate the influence of biological cementation on the strengthening behavior of treated soil. The maximum shear stress improvement between bio-treated and untreated samples was 292% under normal stress of 55.5 kN as a result of an increase in interparticle cohesion parameters.

Investigation of Cement Prepared with Microencapsulated Microorganisms

Cracks in underground rock masses cause gas leakage, seepage, and water inflow. To realize calcium carbonate deposition and mineralization filling in rock cracks, microencapsulated bacterial spores were prepared by an oil phase separation method. To optimize the microorganism growth conditions, the effects of microcapsules with various pHs, particle sizes, and amounts on microcrack self-healing were investigated through an orthogonal test, and the best conditions for repairing the cracks using microencapsulated Bacillus sphaericus were obtained. Infrared analysis and scanning electron microscopy were used to observe the morphological characteristics and coating performance of the microcapsules. The results showed that the microcapsules contained functional groups in the core and wall materials. The surfaces of the microcapsules prepared by the test were rough, which was beneficial for adhesion onto the fracture surface. X-ray diffraction analysis, X-ray photoelectron spectroscopy, and thermal analysis were conducted. The results showed that the microcapsules with pH = 8 and a particle size of 100 μm had the highest thermal decomposition temperature and the best thermal stability. The elements of the core and wall materials were detected in the microcapsules, and the coating had a beneficial effect. The compression and acoustic emission tests of the specimens embedding microbial capsules with different contents under different working conditions revealed that the two fractures of the specimen were due to the rupture of the microcapsule and the rupture of the rock specimen, indicating the best mechanical triggering properties and compressive properties of the microcapsule.

Dairy manure pellets and palm oil mill effluent as alternative nutrient sources in cultivating Sporosarcina pasteurii for calcium carbonate bioprecipitation

Microbially induced carbonate precipitation (MICP) is a process that hydrolysis urea by microbial urease to fill the pore spaces of soil with induced calcium carbonate (CaCO₃ ) precipitates, which eventually results in improved or solidified soil. This research explored the possibility of using dairy manure pellets (DMP) and palm oil mill effluent (POME) as alternative nutrient sources for Sporosarcina pasteurii cultivation and CaCO₃ bioprecipitation. Different concentrations (20 to 80 g l^-1 ) of DMP and POME were used to propagate the cells of Sporosarcina pasteurii under laboratory conditions. The measured CaCO₃ contents for MICP soil specimens that were treated with bacterial cultures grown in DMP medium (60%, w/v) was 15.30 ±0.04g ml^-1 and POME medium (40%, v/v) was 15.49 ±0.05g ml^-1 after 21 days curing. The scanning electron microscopy showed that soil treated with DMP had rhombohedral structure-like crystals with smooth surfaces, while that of POME entailed ring-like cubical formation with rough surfaces Electron dispersive X-ray analysis was able to identify a high mass percentage of chemical element compositions (Ca, C, and O), while spectrum from Fourier-transform infrared spectroscopy confirmed the vibration peak intensities for CaCO₃ . Atomic force microscopy further showed clear topographical differences on the crystal surface structures that were formed around the MICP treated soil samples. These nutrient sources (DMP and POME) showed encouraging potential cultivation mediums to address high costs related to bacterial cultivation and biocementation treatment.

Bioanalytical insight into the life of microbial populations: A chemical monitoring of ureolytic bacteria growth

In this publication an alternative approach to investigations of bacterial growth is proposed. Contrary to the conventional physical methods it is based on enzyme activity detection. The procedure for real-time and on-line monitoring of microbial ureolytic activity (applied as a model experimental biosystem) in the flow analysis format is presented. The developed fully-mechanized bioanalytical flow system is composed of solenoid micropumps and microvalves actuated by Arduino microcontroller. The photometric detection based on Nessler reaction is performed using dedicated flow-through optoelectronic detector made of paired light emitting diodes. The developed bioanalytical system allows discrete assaying of microbial urease in the wide range of activity up to 5.4 U mL^-1 with detection limit below 0.44 U mL^-1, a high sensitivity in the linear range of response (up to 200 mV U^-1 mL and relatively high throughput (9 detection per hour). The proposed differential procedure of measurements (i.e. a difference between peaks register for sample with and without external addition of urea is treated as an analytical signal) allows elimination of interfering effects from substrate and products of biocatalysed reaction as well as other components of medium used for microbial growth. The developed bioanalytical system was successfully applied for the control of growth of urease-positive bacteria strains (Proteus vulgaris, Klebsiella pneumoniae and Paracoccus yeei) including examination of effects from various microbial cultivation conditions like temperature, composition of culture medium and amount of substrate required for induction of bacterial enzymatic activity. The developed bioanalytical flow system can be applied for metabolic activity-based estimation of parameters of lag and log phases of microbial growth as well as for detection of decline phase.

Microbially induced calcite precipitation performance of multiple landfill indigenous bacteria compared to a commercially available bacteria in porous media

Microbially Induced Carbonate Precipitation (MICP) is currently viewed as one of the potential prominent processes for field applications towards the prevention of soil erosion, healing cracks in bricks, and groundwater contamination. Typically, the bacteria involved in MICP manipulate their environment leading to calcite precipitation with an enzyme such as urease, causing calcite crystals to form on the surface of grains forming cementation bonds between particles that help in reducing soil permeability and increase overall compressive strength. In this paper, the main focus is to study the MICP performance of three indigenous landfill bacteria against a well-known commercially bought MICP bacteria (Bacillus megaterium) using sand columns. In order to check the viability of the method for potential field conditions, the tests were carried out at slightly less favourable environmental conditions, i.e., at temperatures between 15-17°C and without the addition of urease enzymes. Furthermore, the sand was loose without any compaction to imitate real ground conditions. The results showed that the indigenous bacteria yielded similar permeability reduction (4.79 E-05 to 5.65 E-05) and calcium carbonate formation (14.4–14.7%) to the control bacteria (Bacillus megaterium), which had permeability reduction of 4.56 E-5 and CaCO₃ of 13.6%. Also, reasonably good unconfined compressive strengths (160–258 kPa) were noted for the indigenous bacteria samples (160 kPa). SEM and XRD showed the variation of biocrystals formation mainly detected as Calcite and Vaterite. Overall, all of the indigenous bacteria performed slightly better than the control bacteria in strength, permeability, and CaCO₃ precipitation. In retrospect, this study provides clear evidence that the indigenous bacteria in such environments can provide similar calcite precipitation potential as well-documented bacteria from cell culture banks. Hence, the idea of MICP field application through biostimulation of indigenous bacteria rather than bioaugmentation can become a reality in the near future.

Insights into the influence of cell concentration in design and development of microbially induced calcium carbonate precipitation (MICP) process

Microbially induced calcium carbonate precipitation (MICP) process utilising the biogeochemical reactions for low energy cementation has recently emerged as a potential technology for numerous engineering applications. The design and development of an efficient MICP process depends upon several physicochemical and biological variables; amongst which the initial bacterial cell concentration is a major factor. The goal of this study is to assess the impact of initial bacterial cell concentration on ureolysis and carbonate precipitation kinetics along with its influence on the calcium carbonate crystal properties; as all these factors determine the efficacy of this process for specific engineering applications. We have also investigated the role of subsequent cell recharge in calcium carbonate precipitation kinetics for the first time. Experimental results showed that the kinetics of ureolysis and calcium carbonate precipitation are well-fitted by an exponential logistic equation for cell concentrations between optical density range of 0.1 OD to 0.4 OD. This equation is highly applicable for designing the optimal processes for microbially cemented soil stabilization applications using native or augmented bacterial cultures. Multiple recharge kinetics study revealed that the addition of fresh bacterial cells is an essential step to keep the fast rate of precipitation, as desirable in certain applications. Our results of calcium carbonate crystal morphology and mineralogy via scanning electron micrography, energy dispersive X-ray spectroscopy and X-ray diffraction analysis exhibited a notable impact of cell number and extracellular urease concentration on the properties of carbonate crystals. Lower cell numbers led to formation of larger crystals compared to high cell numbers and these crystals transform from vaterite phase to the calcite phase over time. This study has demonstrated the significance of kinetic models for designing large-scale MICP applications.

A preliminary study of solid-waste coal gangue based biomineralization as eco-friendly underground backfill material: Material preparation and macro-micro analyses

Solid-waste coal gangue (CG) mixed with cement as underground backfilling material is widely applied in coal mines throughout China. However, this material can pollute the environment during its production, preparation, and transportation, which is mainly caused by cement. As a cement-free eco-friendly technology, microbially induced carbonate precipitation (MICP) technology can produce biomineralization products to consolidate loose grains, and the microbial growth environment is adapted to underground temperature with no pollution. To this end, this study gets the Bacillus pasteurii with special resistance by strain domestication, proposes a CG-based bio-mineralized underground backfilling material without using cement, and analyses the characteristics of it from macro- to microscopic perspectives by dissolution test, scanning electron microscopy (SEM), Energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results indicate that strain domestication leads to B. pasteurii, which can withstand CG leaching solution and 1 M urea simultaneously. This satisfies the basic requirements of CG based mineralized material. Through the circulation perfusion method, the intact CG based biomineralized specimens are obtained. Macroscopically, the bacteria bind gangue grains into a whole with high biomineral content (11.66%). The utilization rate of mineralizing solution is up to 66.82% which makes good use of raw materials. Microscopically, a new crystal formation is observed, and CG particles are consolidated well where the crystals precipitate to fill the pores and bind the particles together. Hence this method has a significant influence on the deposition of biominerals. Meanwhile the biomineralization improves the microstructure considerably and bonds the CG particles as a whole. A comprehensive analysis of the test results shows that, from an environment viewpoint, the preliminary study of new CG based bio-mineralized material is successful.

Microbial effect on water sorptivity and sulphate ingress by Bacillus megaterium on mortars prepared using Portland Pozzolana cement

AIMS

To determine the effect of direct embedment of Bacillus megaterium into Portland pozzolana cement mortars on water sorptivity and diffusivity coefficient of sulphate ions.

METHODS AND RESULTS

Prisms with a water/cement ratio of 0·5 were prepared by blending Portland Pozzolana cement with the requisite volume of a B. megaterium (microbial) solution whose concentration was 1·0 × 10⁷ cells per ml. Mortar prisms of 160 mm × 40 mm × 40 mm were fabricated for this study. Mortars cured for 28 days were exposed to 0·2465 mol l^-1 Na₂ SO₄ solution using accelerated ion migration test method for 36-h session using a 12V DC power source. Sulphate ion concentration was then determined through the ingressed mortar at 10 mm interval. A minimum water sorption gain of 0·61% was observed on the prism prepared with and cured in microbial solution. A maximum of 0·0289 and a minimum of 0·0093 water sorptivity coefficients were exhibited by the control prism and microbial prisms, respectively. The microbial prisms exhibited the lowest apparent diffusion coefficient (D_app ) of 4·5179 × 10^-11  m²  s^-1 .

CONCLUSIONS

Direct incorporation of B. megaterium in mortar preparation, curing or both regimes significantly retarded water sorption and lowered sulphate ion ingress. The inclusion of this bacterial in the mortar further complements the pozzolana pore structure benefits.

SIGNIFICANCE AND IMPACT OF THE STUDY

This novel B. megaterium bacteria which can survive and cause biocementation within hydrating cement mortar when not encapsulated would result in a green innovation. Once adopted and applied in real-life scenario, it would promote construction of durable, safe, resilient and affordable shelter.

Non-sterile corn steep liquor a novel, cost effective and powerful culture media for Sporosarcina pasteurii cultivation for sand improvement

AIMS

Microbial induced calcium carbonate precipitation (MICP) is one of the bio-cementation methods for improving granular soils. This study evaluate the feasibility of obtaining a bacterial solution with high optical density and urease activity by an inexpensive corn steep liquor (CSL) medium in non-sterile conditions in order to achieve sand improvement.

METHODS AND RESULTS

Corn steep liquor media with different concentrations (different dilution rates) were prepared and, without any autoclaving (non-sterile conditions), different percentage of the inoculum solutions were added to them and incubated. Effect of inoculum solution percentage and CSL dilution rates on specifications of bacterial solution was evaluated. Urease activity and scanning electron microscope (SEM) and X-Ray Diffraction (XRD) were used to efficiency of CLS media in sand improvement. The considerable urease activity was measured as 5·7 mS cm^-1  min^-1 using nonsterile CLS. By using CYNU (CSL-Yeast extract-NH4Cl-Urea) bacterial solution, the urease activity of 5·5 mS cm^-1  min^-1 for the OD₆₀₀ (optical density at 600 nm) of 1·88 and, consequently, specific urease activity of 2·93 mS cm^-1  min^-1  OD₆₀₀ ^-1 was obtained. The highest unconfined compressive strength (811 kPa) was obtained for the CYNU. XRD revealed new calcite peaks next to the quartz peaks.

CONCLUSIONS

Production of inexpensive bacterial solution using diluted CSL as the inexpensive, effective and powerful culture media for Sporosarcina pasteurii cultivation in nonsterile conditions, allows geotechnical and biotechnological engineers to use MICP technology more widely in land improvement and field-scale bio-cementation and bioremediation projects.

SIGNIFICANCE AND IMPACT OF THE STUDY

Obtaining high urease activity of inexpensive microbial solution using diluted CSL as the culture medium in nonsterile conditions, as the unique results of this study, can be significant in the field of bioremediation studies using MICP.

Biocementation Influence on Flexural Strength and Chloride Ingress by Lysinibacillus sphaericus and Bacillus megaterium in Mortar Structures

The concrete/mortar durability performance depends mainly on the environmental conditions, the microstructures, and its chemistry. Cement structures are subject to deterioration by the ingress of aggressive media. This study focused on the effects of Bacillus megaterium and Lysinibacillus sphaericus on flexural strength and chloride ingress in mortar prisms. Microbial solutions with a concentration of 1.0 × 107 cells/ml were mixed with ordinary Portland cement (OPC 42.5 N) to make mortar prisms at a water/cement ratio of 0.5. Four mortar categories were obtained from each bacterium based on mix and curing solution. Mortar prisms of 160 mm × 40 mm × 40 mm were used in this study. Flexural strength across all mortar categories was determined at the 14th, 28th, and 56th day of curing. Mortars prepared and cured using bacterial solution across all curing ages exhibited the highest flexural strength as well as the highest percent flexural strength gain. Lysinibacillus sphaericus mortars across all mortar categories showed higher flexural strength and percent flexural strength gain than Bacillus megaterium mortars. The highest percent flexural strength gain of 33.3% and 37.0% was exhibited by the 28th and 56th day of curing, respectively. The mortars were subjected to laboratory prepared 3.5% by mass of sodium chloride solution under the accelerated ion migration test method for thirty-six hours using a 12 V Direct Current power source after their 28th day of curing. After subjecting the mortar cubes to Cl media, their core powder was analyzed for Cl content. From these results, the apparent diffusion coefficient, Dapp, was approximated from solutions to Fick’s 2nd Law using the error function. Bacillus megaterium mortars across all mortar categories showed lower apparent diffusion coefficient values with the lowest being 2.6456 × 10–10 while the highest value for Lysinibacillus sphaericus mortars was 2.8005 × 10–10. Both of the test bacteria lowered the ordinary Portland cement Cl-ingress but Bacillus megaterium was significantly more effective than Lysinibacillus sphaericus in inhibition.

Influence of Lysinibacillus sphaericus on compressive strength and water sorptivity in microbial cement mortar

Cement structures are subject to degradation either by aggressive media or development of micro/macro cracks which create external substance ingress pathways. Microbiocementation can be employed as a self-intelligent solution to this deterioration process. This paper presents study results on the effects of Lysinibacillus sphaericus microbiocementation on Ordinary Portland cement (OPC), normal consistency, setting time, soundness, compressive strength and water sorptivity. Microbial solutions with a concentration of 1.0 × 10⁷ cells/ml were mixed with OPC to make prisms at a water/cement ratio of 0.5. Mortar prisms of 160 mm × 40 mm x 40mm were used in this study. A maximum compressive strength gain of 17% and 19.8% was observed on the microbial prism at the 28^th and 56^th day of curing respectively. A minimum of 0.0190 and a maximum of 0.0355 water sorptivity coefficient was observed on the OPC microbial prism and OPC control prism, after 28^th day of curing respectively. Scanning electron microscope images taken after the 28^th day of curing showed formation of vast calcium silicate hydrates and more calcite deposits on microbial mortars. Statistical findings of this study indicate that Lysinibacillus sphaericus significantly retarded both the setting time and normal consistency, but has no influence on the mortar soundness.

Environmental safety and biosafety in construction biotechnology

The topics of Construction Biotechnology are the development of construction biomaterials and construction biotechnologies for soil biocementation, biogrouting, biodesaturation, bioaggregation and biocoating. There are known different biochemical types of these biotechnologies. The most popular construction biotechnology is based on precipitation of calcium carbonate initiated by enzymatic hydrolysis of urea which follows with release of ammonia and ammonium to environment. This review focuses on the hazards and remedies for construction biotechnologies and on the novel environmentally friendly biotechnologies based on precipitation of hydroxyapatite, decay of calcium bicarbonate, and aerobic oxidation of calcium salts of organic acids. The use of enzymes or not living bacteria are the best options to ensure biosafety of construction biotechnologies. Only environmentally safe construction biotechnologies should be used for such environmental and geotechnical engineering works as control of the seepage in dams, channels, landfills or tunnels, sealing of the channels and the ponds, prevention of soil erosion and soil dust emission, mitigation of soil liquefaction, and immobilization of soil pollutants.

Bioprospecting of Ureolytic Bacteria From Laguna Salada for Biomineralization Applications

The processes of biomineralization, mediated by ureolytic bacteria, possess a wide range of technological applications, such as the formation of biocements and remediation of water and soil environments. For this reason, the bioprospecting of new ureolytic bacteria is interesting for its application to these technologies, particularly for water treatment. This study demonstrates the isolation, selection, and identification of halotolerant ureolytic bacteria from Laguna Salada (inland from Atacama Desert) and the evaluation of their ability to precipitate calcium carbonate crystals in freshwater in the presence of calcium ions, as well as the ability to induce the precipitation of crystals from different ions present in seawater. Twenty-four halotolerant ureolytic bacteria whose molecular identification gives between 99 and 100% identity with species of the genus Bacillus, Porphyrobacter, Pseudomonas, Salinivibrio, and Halomonas were isolated. When cultivated in freshwater, urea, and calcium chloride, all species are able to biomineralize calcium carbonate in different concentrations. In seawater, the strains that biomineralize the highest concentration of calcium carbonate correspond to Bacillus subtilis and Halomonas sp. SEM–EDX and XRD analyses determined that both bacteria induce the formation of 9–33% halite (NaCl), 31–66% monohydrocalcite (CaCO₃ × H₂O), and 24–27% struvite (MgNH₄PO₄ × 6H₂O). Additionally, B.subtilis induces the formation of 7% anhydrite (CaSO₄). In seawater, B.subtilis and Halomonas sp. were able to precipitate both calcium (96–97%) and magnesium (63–67%) ions over 14 days of testing. Ion removal assays with B.subtilis immobilized in beads indicate a direct relationship between the urea concentration and a greater removal of ions with similar rates to free cells. These results demonstrate that the biomineralization mediated by bacterial urea hydrolysis is feasible in both freshwater and seawater, and we propose its application as a new technology in improving water quality for industrial uses.

A Low-Tech Bioreactor System for the Enrichment and Production of Ureolytic Microbes

Ureolysis-driven microbially induced carbonate precipitation (MICP) has recently received attention for its potential biotechnological applications. However, information on the enrichment and production of ureolytic microbes by using bioreactor systems is limited. Here, we report a low-tech down-flow hanging sponge (DHS) bioreactor system for the enrichment and production of ureolytic microbes. Using this bioreactor system and a yeast extract-based medium containing 0.17 M urea, ureolytic microbes with high potential urease activity (> 10 μmol urea hydrolyzed per min per ml of enrichment culture) were repeatedly enriched under non-sterile conditions. In addition, the ureolytic enrichment obtained in this study showed in vitro calcium carbonate precipitation. Fluorescence in situ hybridization analysis showed the existence of bacteria of the phylum Firmicutes in the bioreactor system. Our data demonstrate that this DHS bioreactor system is a useful system for the enrichment and production of ureolytic microbes for MICP applications.

Urease-aided calcium carbonate mineralization for engineering applications: A review

Inducing calcium carbonate precipitation is another important function of urease in nature. The process takes advantage of the supply of carbonate ions derived from urea hydrolysis and of an increase in pH generated by the reaction, effects that in the presence of Ca²⁺ ions lead to the precipitation of CaCO₃. Further to its importance in nature, if performed in a biomimetic manner, the urease-aided CaCO₃ mineralization offers enormous potential in innovative engineering applications as an eco-friendly technique operative under mild conditions, to be used for remediation and cementation/deposition in field applications in situ. These include among others, the strengthening and consolidation of soil/sand, the protection and restoration of stone and concrete structures, conservation of stone cultural heritage materials, cleaning waste- and groundwater of toxic metals and radionuclides, and plugging geological formations for the enhancement of oil recovery and geologic CO₂ sequestration. In view of the potential of this newly emerging interdisciplinary branch of engineering, this article presents the principles of urease-aided calcium carbonate mineralization apposed to other biomineralization processes, and reviews the advantages and limitations of the technique compared to the conventional techniques presently in use. Further, it presents areas of its existing and potential applications, notably in geotechnical, construction and environmental engineering, and its future perspectives.

Screening for Urease-Producing Bacteria from Limestone Caves of Sarawak

Urease is a key enzyme in the chemical reaction of microorganism and has been found to be associated withcalcification, which is essential in microbially induced calcite precipitation (MICP) process. Three bacterialisolates (designated as LPB19, TSB31 and TSB12) were among twenty-eight bacteria that were isolated fromsamples collected from Sarawak limestone caves using the enrichment culture technique. Isolates LPB19, TSB31and TSB12 were selected based on their quick urease production when compared to other isolates. Phenotypiccharacteristics indicate all three bacterial strains are gram-positive, rod-shaped, motile, catalase and oxidasepositive. Urease activity of the bacterial isolates were measured through changes in conductivity in the absence ofcalcium ions. The bacterial isolates (LPB19, TSB12 and TSB31) showed urease activity of 16.14, 12.45 and 11.41mM urea hydrolysed/min respectively. The current work suggested that these isolates serves as constitutiveproducers of urease, potentially useful in inducing calcite precipitates.