The role of bacterial urease activity on the uniformity of carbonate precipitation profiles of bio-treated coarse sand specimens

Evaluation of microbial-induced calcite precipitation performance for soil surface improvement and toxicity assessment of the biostabilizer

Microbial-induced calcite precipitation (MICP) is an environmentally friendly process that can be used to enhance soil surface stability against wind erosion. In this study, the performance of the MICP process on soil surface improvement was investigated using Staphylococcus warneri IR-103 bacteria. The biostabilizer, containing S. warneri suspension and a cementation solution consisting of 0.5 mM CaCl2 and 1.5 mM urea, was sprayed on fine-grain soil to induce a surface MICP reaction. Soil surface strength was measured using a penetrometer test, and wind tunnel tests were conducted to evaluate the soil surface's resistance to wind erosion. Scanning electron microscopy (SEM) analysis of the treated soils was conducted to visualize carbonate crystal formations within and on the soil particles. Additionally, X-ray diffraction (XRD) was used to confirm the presence and identify the crystal structures. The ecotoxicological assessment of the biostabilizer was carried out by performing phytotoxicity and oral/dermal/ocular in vivo acute toxicity experiments due to a few case reports of S. warneri's harmfulness and virulence of coagulase-negative staphylococci, highlighting the need for safety measures for workers and end-users. Mixing cementation solution with bacterial suspension in yeast-ammonium chloride medium increased soil strength and durability. The biostabilizer did not harm the seed germination of Agropyron desertorum, and the soil surface remained resistant to wind erosion. Rat oral/dermal acute toxicity tests revealed no adverse effects during the 14-day observation period. The LD50 (median lethal dose) cut-off value of the biostabilizer in oral and dermal administrations was 5000 and 1000 mg/kg body weight, respectively. Ocular administration of a 0.1 mL drop did not induce eye irritation in rabbits. In conclusion, the use of the biostabilizer for wind erosion control appears to be technically and environmentally feasible and justifiable.

Synergistic biocementation: harnessing Comamonas and Bacillus ureolytic bacteria for enhanced sand stabilization

Biocementation, driven by ureolytic bacteria and their biochemical activities, has evolved as a powerful technology for soil stabilization, crack repair, and bioremediation. Ureolytic bacteria play a crucial role in calcium carbonate precipitation through their enzymatic activity, hydrolyzing urea to produce carbonate ions and elevate pH, thus creating favorable conditions for the precipitation of calcium carbonate. While extensive research has explored the ability of ureolytic bacteria isolated from natural environments or culture conditions, bacterial synergy is often unexplored or under-reported. In this study, we isolated bacterial strains from the local eutrophic river canal and evaluated their suitability for precipitating calcium carbonate polymorphs. We identified two distinct bacterial isolates with superior urea degradation ability (conductivity method) using partial 16 S rRNA gene sequencing. Molecular identification revealed that they belong to the Comamonas and Bacillus genera. Urea degradation analysis was performed under diverse pH (6,7 and 8) and temperature (15 °C,20 °C,25 °C and 30 °C) ranges, indicating that their ideal pH is 7 and temperature is 30 °C since 95% of the urea was degraded within 96 h. In addition, we investigated these strains individually and in combination, assessing their microbially induced carbonate precipitation (MICP) in silicate fine sand under low (14 ± 0.6 °C) and ideal temperature 30 °C conditions, aiming to optimize bio-mediated soil enhancement. Results indicated that 30 °C was the ideal temperature, and combining bacteria resulted in significant (p ≤ 0.001) superior carbonate precipitation (14-16%) and permeability (> 10- 6 m/s) in comparison to the average range of individual strains. These findings provide valuable insights into the potential of combining ureolytic bacteria for future MICP research on field applications including soil erosion mitigation, soil stabilization, ground improvement, and heavy metal remediation.

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.

Statistical and machine learning analysis for the application of microbially induced carbonate precipitation as a physical barrier to control seawater intrusion

Seawater intrusion in coastal aquifers is a significant problem that can be addressed through the construction of subsurface dams or physical cut-off barriers. An alternative method is the use of microbially induced carbonate precipitation (MICP) to reduce the hydraulic conductivity of the porous medium and create a physical barrier. However, the effectiveness of this method depends on various factors, and the scientific literature presents conflicting results, making it challenging to generalise the findings. To overcome this challenge, a statistical and machine learning (ML) approach is employed to infer the causes for the reduction in hydraulic conductivity and identify the optimum MICP parameters for preventing seawater intrusion. The study involves data curation, exploratory analysis, and the development of various models to fit the input data (k-Nearest Neighbours - kNN, Support Vector Regression - SVR, Random Forests - RF, Gradient Boosting - XgBoost, Linear model with interaction terms, Ensemble learning algorithms with weighted averages - EnL-WA and stacking - EnL-Stack). The models performed reasonably well in the region where permeability reduction is sensitive to carbonate increase capturing the permeability reduction profile with respect to cementation level while demonstrating that they can be used in initial assessments of the specific conditions (e.g., soil properties). The best performing algorithms were the EnL-Stack and RF followed by XgBoost and SVR. The MICP method is effective in reducing hydraulic conductivity provided that the various biochemical parameters are optimised. Critical biochemical parameters for successful MICP formulations are the bacterial optical density, the urease activity, calcium chloride concentration and flow rate as well as the interaction terms across the properties of the porous media and the biochemical parameters. The models were used to identify the optimum MICP formulation for various porous media properties and the maximum permeability reduction profiles across cementation levels have been derived.

Feeding strategies for Sporosarcina pasteurii cultivation unlock more efficient production of ureolytic biomass for MICP

The bacterium Sporosarcina pasteurii is the most commonly used microorganism for Microbial Induced Calcite Precipitation (MICP) due to its high urease activity. To date, no proper fed-batch cultivation protocol for S. pasteurii has been published, even though this cultivation method has a high potential for reducing costs of producing microbial ureolytic biomass. This study focusses on fed-batch cultivation of S. pasteurii DSM33. The study distinguishes between limited fed-batch cultivation and extended batch cultivation. Simply feeding glucose to a S. pasteurii culture does not seem beneficial. However, it was exploited that S. pasteurii is auxotrophic for two vitamins and amino acids. Limited fed-batch cultivation was accomplished by feeding the necessary vitamins or amino acids to a culture lacking them. Feeding nicotinic acid to a nicotinic acid deprived culture resulted in a 24% increase of the specific urease activity compared to a fed culture without nicotinic acid limitation. Also, extended batch cultivation was explored. Feeding a mixture of glucose and yeast extract results in OD600 of ≈70 at the end of cultivation, which is the highest value published in literature so far. These results have the potential to make MICP applications economically viable.

Effect of surfactant on urease-producing flora from waste activated sludge using microbially induced calcite precipitation technology to suppress coal dust

The wettability of microbially induced calcite precipitation (MICP) is a challenge in dust suppression. Herein, the tolerance of urease-producing flora to surfactants was investigated. The optimal tolerance concentrations of the urease-producing flora to sodium dodecylbenzene sulfonate (SDBS, anionic surfactant), alkyl polyglycoside (APG, non-ionic surfactant), and cocamidopropyl betaine (CAB, zwitterionic surfactant), and were 0.2%, 0.1%, and 0.05%. The cetyltrimethylammonium bromide (CTAB, cationic surfactant) inhibited urease production by urease-producing flora. The mineralization products of SDBS, APG, and CAB treatments were all transformed into calcite. The wind resistance test showed that the mass loss of all samples is less than 0.1%. The rain resistance and hardness tests showed that 0.2% SBDS had the best effect, followed by 0.1% APG and 0.05% CAB, and finally, No surfactants. Microbiome analysis showed that the abundance of Sporosarcina and Unclassified_bacillaceae reduced, and the intense competition between Paenalcaligenes and Sporosarcina are essential reasons for reducing urease activity. SDBS and APG could reduce the pathogenic risk of microbial dust suppressants. This study will facilitate the practical application of microbial dust suppressants.

Insight into biomolecular interaction-based non-classical crystallization of bacterial biocement

In an attempt to draw a correlation between calcium carbonate (CaCO3) precipitation and biomacromolecules such as extracellular polymeric substances and enzyme activity in biomineralizing microbe, this report aims to elucidate the ureolytic and ammonification route in Paenibacillus alkaliterrae to explore the possible role of organic biomolecule(s) present on cell surface in mediating nucleation and crystallization of biogenic CaCO3. After 168 h of biomineralization in ureolysis and ammonification, 2.2 g/l and 0.87 g/l of CaCO3 precipitates were obtained, respectively. The highest carbonic anhydrase activity (31.8 µmoles/min/ml) was evidenced in ammonification as opposed to ureolysis (24.8 µmoles/min/ml). Highest urease activity reached up to 9.26 µmoles/min/ml in ureolytic pathway. Extracellular polymeric substances such as polysaccharides and proteins were found to have a vital role not only in the nucleation and crystal growth but also in addition direct polymorphic fate of CaCO3 nanoparticles. EPS production was higher during ammonification (3.1 mg/ml) than in ureolysis (0.72 mg/ml). CaCO3 nanoparticle-associated proteins were found to be 0.82 mg/ml in ureolysis and 0.56 mg/ml in ammonification. After 30 days of biomineralization, all the polymorphic forms stabilized to calcite in ureolysis but in ammonification vaterite predominated. In our study, we showed that organic template-mediated prokaryotic biomineralization follows the non-classical nucleation and varying proportions of these organic components causes selective polymorphism of CaCO3 nanoparticles. Overall, the findings are expected to further the fundamental understanding of enzymes, EPS-driven non-classical nucleation of CaCO3, and we foresee the design of fit-for-purpose futuristic biominerals arising from such renewed understanding of biomineralization. KEY POINTS: • Organic-inorganic interface of cell surface promote crystallization of biominerals • Carbohydrate and proteins in the interface results selective polymorphism of CaCO3 • Calcite stabilized at 30 days in ureolysis, vaterite-calcite mix in ammonification.

Microbially Induced Calcium Carbonate Precipitation by Sporosarcina pasteurii: a Case Study in Optimizing Biological CaCO3 Precipitation

Current production of traditional concrete requires enormous energy investment that accounts for approximately 5 to 8% of the world's annual CO2 production. Biocement is a building material that is already in industrial use and has the potential to rival traditional concrete as a more convenient and more environmentally friendly alternative. Biocement relies on biological structures (enzymes, cells, and/or cellular superstructures) to mineralize and bind particles in aggregate materials (e.g., sand and soil particles). Sporosarcina pasteurii is a workhorse organism for biocementation, but most research to date has focused on S. pasteurii as a building material rather than a biological system. In this review, we synthesize available materials science, microbiology, biochemistry, and cell biology evidence regarding biological CaCO3 precipitation and the role of microbes in microbially induced calcium carbonate precipitation (MICP) with a focus on S. pasteurii. Based on the available information, we provide a model that describes the molecular and cellular processes involved in converting feedstock material (urea and Ca2+) into cement. The model provides a foundational framework that we use to highlight particular targets for researchers as they proceed into optimizing the biology of MICP for biocement production.

Assessment of the Composition Effect of a Bio-Cementation Solution on the Efficiency of Microbially Induced Calcite Precipitation Processes in Loose Sandy Soil

Soil properties are the most important factors determining the safety of civil engineering structures. One of the soil improvement methods studied, mainly under laboratory conditions, is the use of microbially induced calcite precipitation (MICP). Many factors influencing the successful application of the MICP method can be distinguished; however, one of the most important factors is the composition of the bio-cementation solution. This study aimed to propose an optimal combination of a bio-cementation solution based on carbonate precipitation, crystal types, and the comprehensive strength of fine sand after treatment. A series of laboratory tests were conducted with the urease-producing environmental strain of bacteria B. subtilis, using various combinations of cementation solutions containing precipitation precursors (H2NCONH2, C6H10CaO6, CaCl2, MgCl2). To decrease the environmental impact and increase the efficiency of MICP processed, the addition of calcium lactate (CaL) and Mg ions was evaluated. This study was conducted in Petri dishes, assuming a 14-day soil treatment period. The content of water-soluble carbonate precipitates and their mineralogical characterization, as well as their mechanical properties, were determined using a pocket penetrometer test. The studies revealed that a higher concentration of CaL and Mg in the cementation solution led to the formation of a higher amount of precipitates during the cementation process. However, the crystal forms were not limited to stable forms, such as calcite, aragonite, (Ca, Mg)-calcite, and dolomite, but also included water-soluble components such as nitrocalcite, chloro-magnesite, and nitromagnesite. The presence of bacteria allowed for the increasing of the carbonate content by values ranging from 15% to 42%. The highest comprehensive strength was achieved for the bio-cementation solution containing urea (0.25 M), CaL (0.1 M), and an Mg/Ca molar ratio of 0.4. In the end, this research helped to achieve higher amounts of precipitates with the optimum combination of bio-cementation solutions for the soil improvement process. However, the numerical analysis of the precipitation processes and the methods reducing the environmental impact of the technology should be further investigated.

Biologically-induced synthetic manganese carbonate precipitate (BISMCP) for potential applications in heavy metal removal

Heavy metal pollution of water is a burning issue of today's world. Among several strategies involved for heavy metal remediation purpose, biomineralization has shown great potential. Of late, research has been focused on developing effective mineral adsorbents with reduced time and cost consumption. In this present paper, the Biologically-Induced Synthetic Manganese Carbonate Precipitate (BISMCP) was produced based on the biologically-induced mineralization method, employing Sporosarcina pasteurii in aqueous solutions containing urea and MnCl₂. The prepared adsorbent was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), SEM-energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and BET surface area analyzer. EDX analysis showed the elements in the crystal BISMCP were Mn, C, and O. XRD result of BISMCP determined the crystal structure, which is close to rhodochrosite (MnCO₃). Spectral peaks of FTIR at 1641.79 cm^-1 confirmed the appearance of C[bond, double bond]O binding, with strong stretching of CO₃^2- in Amide I. From the six kinds of BISMCP produced, sample MCP-6 has the higher specific surface area by BET analysis at 109.01 m²/g, with pore size at 8.76 nm and higher pore volume at 0.178 cm³/g. These specifications will be suitable as an adsorbent for heavy metal removal by adsorption process. This study presents a preliminary analysis of the possibility of BISMCP for heavy metals adsorption using ICP multi-element standard solution XIII (As, Cr, Cd, Cu, Ni, and Zn). BISMCP formed from 0.1 MnCl₂ and 30 ml of bacteria volume (MCP-6) produced a better adsorbent material than others concentrations, with the adsorption efficiency of total As at 98.9%, Cr at 97.0%, Cu at 94.7%, Cd at 88.3%, Zn at 48.6%, and Ni at 29.5%. Future work could be examined its efficiency adsorbing individual heavy metals.

New non-ureolytic heterotrophic microbial induced carbonate precipitation for suppression of sand dune wind erosion

The detrimental effects of sand storms on agriculture, human health, transportation network, and infrastructures pose serious threats in many countries worldwide. Hence, wind erosion is considered a global challenge. An environmental-friendly method to suppress wind erosion is to employ microbially induced carbonate precipitation (MICP). However, the by-products of ureolysis-based MICP, such as ammonia, are not favorable when produced in large volumes. This study introduces two calcium formate-bacteria compositions for non-ureolytic MICP and comprehensively compares their performance with two calcium acetate-bacteria compositions, all of which do not produce ammonia. The considered bacteria are Bacillus subtilis and Bacillus amyloliquefaciens. First, the optimized values of factors controlling CaCO₃ production were determined. Then, wind tunnel tests were performed on sand dune samples treated with the optimized compositions, where wind erosion resistance, threshold detachment velocity, and sand bombardment resistance were measured. An optical microscope, scanning electron microscope (SEM), and X-ray diffraction analysis were employed to evaluate the CaCO₃ polymorph. Calcium formate-based compositions performed much better than the acetate-based compositions in producing CaCO₃. Moreover, B. subtilis produced more CaCO₃ than B. amyloliquefaciens. SEM micrographs clearly illustrated precipitation-induced active and inactive bounds and imprints of bacteria on CaCO₃. All compositions considerably reduced wind erosion.

Isolation of urease-producing bacteria from cocoa farms soils in Santander, Colombia, for cadmium remediation

Cadmium (Cd) is a toxic heavy metal that causes serious health problems and is present in agriculturally important soils in Colombia, such as the ones used for cocoa farming. Recently, the use of ureolytic bacteria by the Microbiologically Induced Carbonate Precipitation (MICP) activity has been proposed as an alternative to mitigate the availability of Cd in contaminated soils. In this study, 12 urease-positive bacteria able to grow in the presence of Cd(II) were isolated and identified. Three were selected based on urease activity, precipitates formation and growth, with two belonging to the genus Serratia (codes 4.1a and 5b) and one to Acinetobacter (code 6a). These isolates exhibited low urease activity levels (3.09, 1.34 and 0.31 μmol mL-1 h-1, respectively), but could raise the pH to values close to 9.0 and to produce carbonate precipitates. It was shown that the presence of Cd affects the growth of the selected isolates. However, urease activity was not negatively influenced. In addition, the three isolates were observed to efficiently remove Cd from solution. The two Serratia isolates presented maximum removals of 99.70% and 99.62%, with initial 0.05 mM Cd(II) in the culture medium (supplemented with urea and Ca(II)) at 30 °C and 144 h of incubation. For the Acinetobacter isolate, the maximum removal was 91.23% at the same conditions. Thus, this study evidences the potential use of these bacteria for bioremediation treatments in samples contaminated with Cd, and it is one of the few reports that shows the high cadmium removal capacity of bacteria from the genus Serratia.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03495-1.

Influencing factors on ureolytic microbiologically induced calcium carbonate precipitation for biocementation

Microbiologically induced calcium carbonate precipitation (MICP) is a technique that has received a lot of attention in the field of geotechnology in the last decade. It has the potential to provide a sustainable and ecological alternative to conventional consolidation of minerals, for example by the use of cement. From a variety of microbiological metabolic pathways that can induce calcium carbonate (CaCO₃) precipitation, ureolysis has been established as the most commonly used method. To better understand the mechanisms of MICP and to develop new processes and optimize existing ones based on this understanding, ureolytic MICP is the subject of intensive research. The interplay of biological and civil engineering aspects shows how interdisciplinary research needs to be to advance the potential of this technology. This paper describes and critically discusses, based on current literature, the key influencing factors involved in the cementation of sand by ureolytic MICP. Due to the complexity of MICP, these factors often influence each other, making it essential for researchers from all disciplines to be aware of these factors and its interactions. Furthermore, this paper discusses the opportunities and challenges for future research in this area to provide impetus for studies that can further advance the understanding of MICP.

Mechanism of microbiologically induced calcite precipitation for cadmium mineralization

Microbiologically induced calcite precipitation (MICP) technology shows potential for remediating heavy metal pollution; however, the underlying mechanism of heavy metal mineralization is not well-understood, limiting the application of this technology. In this study, we targeted Cd contamination (using 15:1, 25:1, and 50:1 Ca²⁺/Cd²⁺ molar ratios) and showed that the ureolytic bacteria Sporosarcina ureilytica ML-2 removed >99.7 % Cd²⁺ with a maximum fixation capacity of 75.61 mg-Cd/g-CaCO₃ and maximum precipitation production capacity of 135.99 mg-CaCO₃/mg-cells. Quantitative PCR analysis showed that Cd²⁺ inhibited the expression of urease genes (ureC, ureE, ureF, and ureG) by 70 % in the ML-2 strain. Additionally, the pseudo-first-order kinetics model (R² = 0.9886), intraparticle diffusion model (R² = 0.9972), and Temkin isotherm model (R² = 0.9828) described the immobilization process of Cd²⁺ by bio calcite in MICP-Cd system. The three Cd²⁺ mineralization products generated by MICP were attributed to surface precipitation (Cd²⁺ → Cd(OH)₂), direct binding with the CO₃^2-/substitution calcium site of calcite (Cd²⁺ → CdCO₃, otavite), and calcite lattice vacancy anchors (Cd²⁺ → (Ca_xCd_1-x)CO₃). Our findings improve the understanding of the mechanisms by which MICP can achieve in situ stabilization of heavy metals.

Incorporation of Mixing Microbial Induced Calcite Precipitation (MICP) with Pretreatment Procedure for Road Soil Subgrade Stabilization

Microbial induced carbonate precipitation (MICP) provides an alternative method to stabilize the soil. To further improve the reinforcement effect, this study aims to propose a strategy by incorporating the mixing MICP method with pretreatment procedure. A series of laboratory tests were performed to investigate the preparation parameters (including the moisture content and dry density of the soil, the concentration of urea and CaCl₂ in cementation solution), the engineering properties, the CaCO₃ distribution as well as the mineralogical and micro structural characteristics of pretreatment-mixing MICP reinforced soil (PMMRS). Based on the orthogonal experiment results, the optimum preparation parameters for PMMRS were determined. The UCS of PMMRS was more strongly dependent on the moisture content and concentration of CaCl₂ than the concentration ratio of CaCl₂ to urea. Moreover, it was testified that incorporation of pretreatment procedure improved the stabilization effect of traditional mixing MICP method on the clayed sand (CLS). The UCS of PMMRS specimen was increased by 198% and 78% for the pure CLS and the simple mixing MICP reinforced soil, respectively. Furthermore, the CaCO₃ products generated consisted of the aragonite, calcite and vaterite, which distributed unevenly inside the specimen no matter the lateral or vertical direction. The reason for the uneven distribution might be that oxygen content varied with the regions in different directions, and hence affected the mineralization reaction. In addition, the mineralization reaction would affect the pore structure of the soil, which was highly related to the stabilization effect of MICP reinforced soil.

Developing a fluorometric urease activity microplate assay suitable for automated microbioreactor experiments

Quantifying urease activity is an important task for Microbial Induced Calcite Precipitation research. A new urease activity microplate assay using a fluorescent pH indicator is presented. The method is also suitable for automated measurements during microbioreactor experiments. The assay reagent consists of the green fluorescent pH-indicator fluorescein, urea and a phosphate buffer. After sample addition, the microbial urease hydrolyses urea, which results in a pH and hence fluorescence increase. The fluorescence signal can be measured with a microplate reader or with the microbioreactor system BioLector, allowing for automated urease activity measurements during cultivation experiments. In both measurement systems, the fluorescence signal slope highly correlates with the urease activity measured offline with standard methods. Automated measurement is possible, as no sample preparation such as centrifugation or adjusting of the optical density is required. The assay was developed so that the culture samples turbidity, salinity or buffer concentration does not have a negative impact on the fluorescence signal. The assay allows for straightforward, non-hazardous, parallelized, cheap and reliable measurements, making research on ureolytic bacteria for Microbial Induced Calcite Precipitation more efficient. The assay could be adapted to other enzymes, which have a strong impact on the pH value.

Sporosarcina pasteurii can be used to print a layer of calcium carbonate

When using microbiologically induced calcium carbonate precipitation (MICP) to produce calcium carbonate crystals in the cavities between mineral particles to consolidate them, the inhomogeneous distribution of the precipitated calcium carbonate poses a problem for the production of construction materials with consistent parameters. Various approaches have been investigated in the literature to increase the homogeneity of consolidated samples. One approach can be the targeted application of ureolytic organisms by 3D printing. However, to date, this possibility has been little explored in the literature. In this study, the potential to use MICP to print calcium carbonate layers on mineral particles will be investigated. For this purpose, a dispensing unit was modified to apply both a suspension of Sporosarcina pasteurii and a calcination solution containing urea and calcium chloride onto quartz sand. The study showed that after passing through the nozzle, S. pasteurii preserved consistent cell vitality and therefore its potential of MICP. Applying cell suspension and calcination solution through a printing nozzle resulted in a layer of calcium carbonate crystals on quartz sand. This observation demonstrated the proof of concept of printing calcium carbonate by MICP through the nozzle of a dispensing unit. Furthermore, it was shown that cell suspensions of S. pasteurii can be stored at 4°C for a period of 17 days while maintaining its optical density, urease activity and cell vitality and therefore the potential for MICP. This initial concept could be extended in further research to printing three-dimensional (3D) objects to solve the problem of homogeneity in consolidated mineral particles.

A review on the applications of microbially induced calcium carbonate precipitation in solid waste treatment and soil remediation

Improper disposal and accumulation of solid waste can cause a number of environmental problems, such as the heavy metal contamination of soil. Microbially induced calcium carbonate precipitation (MICP) is considered as a promising technology to solve many environmental problems. Calcium-based solid waste can be utilized as an alternative source of calcium for the MICP process, and carbonate-based biominerals can be used for soil remediation, solid waste treatment, remediation of construction concrete, and generation of bioconcrete. This paper describes the metabolic pathways and mechanisms of microbially induced calcium carbonate precipitation and highlights the value of MICP for solid waste treatment and soil remediation applications. The factors affecting the effectiveness of MICP are discussed and analyzed through an overview of recent studies on the application of MICP in environmental engineering. The paper also summarizes the current challenges for the large-scale application of this innovative technology. In prospective study, MICP can be an effective alternative to conventional technologies in solid waste treatment, soil remediation and CO₂ sequestration, as it can reduce negative environmental impacts and provide long-term economic benefits.

New Biocalcifying Marine Bacterial Strains Isolated from Calcareous Deposits and Immediate Surroundings

Marine bacterial biomineralisation by CaCO3 precipitation provides natural limestone structures, like beachrocks and stromatolites. Calcareous deposits can also be abiotically formed in seawater at the surface of steel grids under cathodic polarisation. In this work, we showed that this mineral-rich alkaline environment harbours bacteria belonging to different genera able to induce CaCO3 precipitation. We previously isolated 14 biocalcifying marine bacteria from electrochemically formed calcareous deposits and their immediate environment. By microscopy and µ-Raman spectroscopy, these bacterial strains were shown to produce calcite-type CaCO3. Identification by 16S rDNA sequencing provided between 98.5 and 100% identity with genera Pseudoalteromonas, Pseudidiomarina, Epibacterium, Virgibacillus, Planococcus, and Bhargavaea. All 14 strains produced carbonic anhydrase, and six were urease positive. Both proteins are major enzymes involved in the biocalcification process. However, this does not preclude that one or more other metabolisms could also be involved in the process. In the presence of urea, Virgibacillus halodenitrificans CD6 exhibited the most efficient precipitation of CaCO3. However, the urease pathway has the disadvantage of producing ammonia, a toxic molecule. We showed herein that different marine bacteria could induce CaCO3 precipitation without urea. These bacteria could then be used for eco-friendly applications, e.g., the formation of bio-cements to strengthen dikes and delay coastal erosion.

Effects of Atrazine on Chernozem Microbial Communities Evaluated by Traditional Detection and Modern Sequencing Technology

Atrazine is a long residual herbicide commonly used in maize fields. Although atrazine can effectively control weeds and improve crop yield, long-term application leads to continuous pollution in the agricultural ecological environment, especially in the soil ecosystem, and its impact on soil microorganisms is still not clear. Four methods were used in the experiment to clarify the effect of atrazine on the bacterial populations of cultivated soil layers of chernozem in a cold region in different periods: high-performance liquid chromatography (HPLC), colorimetry, microplate, and high-throughput sequencing. The level of residual atrazine in cold chernozem decreased from 4.645 to 0.077 mg/kg soil over time, and the residue gradually leached into deep soil and then decreased after accumulating to a maximum value. Atrazine significantly affected the activities of urease and polyphenol oxidase activity in the soil layers at different periods but had no significant effect on sucrase and phosphatase activity. Atrazine significantly reduced the diversity of microbial carbon source utilization and total activity in soil layers of 0-10 and 20-30 cm but only reduced the diversity of microbial carbon source utilization in the 10-20 cm layer. Atrazine had no significant effect on bacterial populations (10-12 phyla, 29-34 genera), but had a slight effect on the relative abundance of various groups. Atrazine significantly reduced the diversity of bacterial populations in cultivated soil layers of chernozem in a cold region, and the diversity of bacterial populations decreased with decreased residue. This lays a foundation for guiding the safe use of herbicides on farmland in Northeast China.

Tensile Strength of Artificially Cemented Sandstone Generated via Microbially Induced Carbonate Precipitation

Artificially bio-cemented sands treated with microbially induced calcite precipitation are weakly cemented rocks representing intermediate materials between locked and carbonate sands. Variations in cementation significantly affect the strength of sample, particularly tensile stregth. The modes of fracture and the surface characteristics resulting from the indirect tensile strength tests (Brazilian tests) are strongly correlated with the specimen strength and consequently the degree of cementation. This study examines the tensile strength of bio-cemented fine and coarse sands (average particle diameter 0.18 and 1.82 mm, respectively) and investigates failure modes by recording fracture evolution at both sides of specimen and surface characteristics of the reconstructed surfaces. The dimensionless slope parameter Z2 provided the best fit with respect to tensile strength while the power spectral density was a good indicator of surface anisotropy. Finally, wavelet decomposition allowed for comparison of fracture surface characteristics of the two sands ignoring the grain size effects.