Crystal transformation and self-assembly theory of microbially induced calcium carbonate precipitation

Biogenic calcium improved Cd2+ and Pb2+ immobilization in soil using the ureolytic bacteria Bacillus pasteurii

Bioremediation based on microbial-induced carbonate precipitation (MICP) was conducted in cadmium and lead contaminated soil to investigate the effects of MICP on Cd and Pb in soil. In this study, soil indigenous nitrogen was shown to induce MICP to stabilize heavy metals without inputting exogenous urea. The results showed that applying Bacillus pasteurii coupled with CaCl2 reduced Cd and Pb bioavailability, which could be clarified through the proportion of exchangeable Cd and Pb in soil decreasing by 23.65 % and 12.76 %, respectively. Moreover, B. pasteurii was combined separately with hydroxyapatite (HAP), eggshells (ES), and oyster shells (OS) to investigate their effects on soil heavy metals' chemical fractions, toxicity characteristic leaching procedure (TCLP)-extractable Cd and Pb as well as enzymatic activity. Results showed that applying B. pasteurii in soil significantly decreased the heavy metals in the exchangeable fraction and increased them in the carbonate phase fraction. When B. pasteurii was combined with ES and OS, the content of carbonate-bound Cd increased by 114.72 % and 118.81 %, respectively, significantly higher than when B. pasteurii was combined with HAP, wherein the fraction of carbonate-bound Cd increased by 86 %. The combination of B. pasteurii and biogenic calcium effectively reduced the leached contents of Cd and Pb in soil, and the TCLP-extractable Cd and Pb fractions decreased by 43.88 % and 30.66 %, respectively, in the BP + ES group and by 52.60 % and 41.77 %, respectively, in the BP + OS group. This proved that MICP reduced heavy metal bioavailability in the soil. Meanwhile, applying B. pasteurii and calcium materials significantly increased the soil urease enzyme activity. The microstructure and chemical composition of the soil samples were studied, and the results from scanning electron microscope, Fourier transform infra-red spectroscopy, and X-ray diffraction demonstrated the MICP process and identified the formation of CaCO3, Ca0.67Cd0.33CO3, and PbCO3 in heavy metal-contaminated soil.

Understanding the Mechanics of the Temporomandibular Joint Osteochondral Interface from Micro- and Nanoscopic Perspectives

The condylar cartilage of the temporomandibular joint (TMJ) is connected to the subchondral bone by an osteochondral interface that transmits loads without causing fatigue damage. However, the microstructure, composition, and mechanical properties of this interface remain elusive. In this study, we found that structurally, a spatial gradient assembly of hydroxyapatite (HAP) particles exists in the osteochondral interface, with increasing volume of apatite crystals with depth and a tendency to form denser and stacked structures. Combined with nanoindentation, this complex assembly of nanoscale structures and components enhanced energy dissipation at the osteochondral interface, achieving a smooth stress transition between soft and hard tissues. This study comprehensively demonstrates the elemental composition and complex nanogradient spatial assembly of the osteochondral interface at the ultramicroscopic scale, providing a basis for exploring the construction of complex mechanical models of the interfacial region.

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.

Steerable artificial magnetic bacteria with target delivery ability of calcium carbonate for soil improvement

The microbial-induced carbonate precipitation (MICP) has acquired significant attention due to its immense potential in sustainable engineering applications, particularly in soil improvement. However, the precise control of microbial-induced calcium carbonate precipitation remains a formidable challenge in engineering practices, owing to the uncertain movement paths of bacteria and the nonuniform distribution of soil pores. Taking inspiration from targeted therapy in medicine, this paper presents novel research on the development and validation of magnetically responsive bacteria. These bacteria demonstrate the ability to target calcium carbonate precipitation in a microfluidic chip, thereby promoting an environmentally friendly and ecologically sustainable biomineralization paradigm. The study focuses on investigating the migration of magnetite nanoparticles (MNPs) in aqueous solutions and enhancing the stability of MNP culture liquids. A specially designed microfluidic chip is utilized to simulate natural sand particles and their pores, while an external magnetic field is applied to precisely control the movement path of the artificial magnetic bacteria, enabling targeted precipitation of calcium carbonate at the micron-scale. Verification of the engineered artificial magnetic bacteria and their ability to induce calcium carbonate precipitation is conducted through SEM-EDS analysis, microfluidic chip observations, and the application of the K-means algorithm and ImageJ software to analyze calcium carbonate formation. The influence of the concentration of magnetic nanoparticles on the calcium carbonate production rate was also studied. The results confirm the potential of the artificial magnetic bacteria for future engineering applications. KEY POINTS: • Sporosarcina pasteurii is first time successfully engineered into artificial magnetic bacteria. • The artificial magnetic bacteria show excellent performance of targeted transportation and directional deposition of CaCO3 in microfluidic chip. • The emergence of artificial magnetic bacteria promotes paradigm shift of next generation environmentally friendly biomineralization.

Experimental Study on the Effect of an Organic Matrix on Improving the Strength of Tailings Strengthened by MICP

In order to improve the effect of microbial-induced calcium carbonate precipitation (MICP) in tailings reinforcement, sodium citrate, an organic matrix with good water solubility, was selected as the crystal form adjustment template for inducing calcium carbonate crystallization, and the reinforcements of tailings by MICP were conducted in several experiments. The effects of sodium citrate on the yield, crystal form, crystal appearance, and distribution of calcium carbonate were analyzed by MICP solution test; thus, the related results were obtained. These showed that the addition of a proper amount of organic matrix sodium citrate could result in an increment in the yield of calcium carbonate. The growth rate of calcium carbonate reached 22.6% under the optimum amount of sodium citrate, and the crystals of calcium carbonate were diverse and closely arranged. Based on this, the MICP reinforcement test of tailings was carried out under the action of the optimum amount of sodium citrate. The microscopic analysis using CT and other means showed that the calcium carbonate is distributed more uniformly in tailings, and the porosity of samples is significantly reduced by layered scanning analysis. The results of triaxial shear tests showed that adding organic matrix sodium citrate effectively increased the cohesion, internal friction angle, and peak stress of the reinforced tailings. It aims to provide a novel idea, a creative approach, and a method to enhance the reinforcement effect of tailings and green solidification technology in the mining environment.

Simultaneous removal of phosphate, calcium, and ammonia nitrogen in a hydrogel immobilized reactor with bentonite/lanthanum/PVA based on microbial induced calcium precipitation

In recent years, it is urgent to solve nitrogen and phosphorus pollution in domestic wastewater. The target strain Pseudomonas sp. Y1 was immobilized using polyvinyl alcohol (PVA) matrix coupled with bentonite and lanthanum (La), respectively, to fabricate four hydrogel materials that used to construct bioreactors. The optimal operating parameters and dephosphorization mechanism were discussed, and the effects of hydrogel materials and different loads on the performance of the bioreactor were contrastively analyzed. The results manifested that when the hydraulic retention time (HRT) was 6.0 h, the C/N was 6.0, and the Ca²⁺ concentration was 100.0 mg L^-1, the bioreactors had the best heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization capacity, and the maximum removal efficiencies of Ca²⁺, PO₄^3--P, and NH₄⁺-N were 82.57, 99.17, and 89.08%, respectively. The operation data indicated that the addition of bentonite significantly promoted HNAD, and the bioreactor had stronger dephosphorization ability in the presence of La. The main phosphorous removal mechanisms were confirmed to be adsorption and co-precipitation. Finally, high-throughput sequencing results indicated that Pseudomonas accounted for the paramount proportion in the bioreactor, and the prediction of functional genes indicated that the C/N of 6.0 is more favorable for the expression of nitrogen removal-related functional genes in the bioreactor system. This study highlights the superiority of microbial induced calcium precipitation (MICP) combined with PVA hydrogel, and provides a theoretical basis for simultaneous nitrogen and phosphate removal of wastewater.

Microencapsulated reactor for simultaneous removal of calcium, fluoride and phenol using microbially induced calcium precipitation: Mechanism and functional characterization

Fluoride ions (F^-) and phenol in groundwater have become a great hurdle to the pursuit of a healthy drinking water source. This study established a microencapsulated immobilization reactor with Aquabacterium sp. CZ3 for the simultaneous removal of nitrate (NO₃^--N), calcium (Ca²⁺), F^-, and phenol from groundwater with 100%, 67.84%, 88.67%, and 100% removal efficiencies, respectively. The three-dimensional mesh structure of microcapsules facilitated the transport and metabolism of substances, while their synergistic effect with bacteria promoted the removal of contaminants. F^- was removed by co-precipitation to generate Ca₅(PO₄)₃F and CaF₂ and adsorption. On one hand, the phenol toxicity promoted the production of extracellular polymers and improved the tolerance of bacteria; on the other hand, the degradation of phenol provided a carbon source for bacteria and promoted the denitrification. The development of microencapsulated immobilized reactor provided a clear mechanism for phenol and F^- removal under the microbially induced calcium precipitation (MICP) technique, while providing a valuable solution for the treatment of complex groundwater resources.