Mechanism of urea decomposition catalyzed by Sporosarcina pasteurii urease based on quantum chemical calculations

Microbially induced calcium carbonate precipitation through CO2 sequestration via an engineered Bacillus subtilis

BACKGROUND

Microbially induced calcium carbonate precipitation has been extensively researched for geoengineering applications as well as diverse uses within the built environment. Bacteria play a crucial role in producing calcium carbonate minerals, via enzymes including carbonic anhydrase-an enzyme with the capability to hydrolyse CO2, commonly employed in carbon capture systems. This study describes previously uncharacterised carbonic anhydrase enzyme sequences capable of sequestering CO2 and subsequentially generating CaCO3 biominerals and suggests a route to produce carbon negative cementitious materials for the construction industry.

RESULTS

Here, Bacillus subtilis was engineered to recombinantly express previously uncharacterised carbonic anhydrase enzymes from Bacillus megaterium and used as a whole cell catalyst allowing this novel bacterium to sequester CO2 and convert it to calcium carbonate. A significant decrease in CO2 was observed from 3800 PPM to 820 PPM upon induction of carbonic anhydrase and minerals recovered from these experiments were identified as calcite and vaterite using X-ray diffraction. Further experiments mixed the use of this enzyme (as a cell free extract) with Sporosarcina pasteurii to increase mineral production whilst maintaining a comparable level of CO2 sequestration.

CONCLUSION

Recombinantly produced carbonic anhydrase successfully sequestered CO2 and converted it into calcium carbonate minerals using an engineered microbial system. Through this approach, a process to manufacture cementitious materials with carbon sequestration ability could be developed.

The Mechanism of Anticorrosion Performance and Mechanical Property Differences between Seawater Sea-Sand and Freshwater River-Sand Ultra-High-Performance Polymer Cement Mortar (UHPC)

There are abundant sea-sand resources on the earth. Traditional sea-sand concrete faced various problems relating to insufficient anticorrosion ability. In this paper, artificial seawater, sea sand, industrial waste, steel fiber, and polycarboxylate superplasticizer were used to prepare ultra-high-performance polymer cement mortar (SSUHPC). At the same time, freshwater river-sand ultra-high-performance polymer cement mortar (FRUHPC) with the same mixing ratio was prepared for comparative study. The compressive strength of SSUHPC reached 162.1 MPa, while the that of FRUHPC reached 173.3 MPa, which was slightly higher. Meanwhile, SSUHPC showed excellent anticorrosion characteristics in terms of carbonization, frost resistance and chloride resistance, and especially for sulfate resistance. The composition of SSUHPC was separated into three parts: mortar, pore and steel fiber, and the performance difference mechanisms of SSUHPC and FRUHPC were investigated by X-ray computed tomography (X-CT), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The hydration degree of mortar in SSUHPC was higher, with higher content of CSH and CH, and its better optimized gel pore characteristics gave SSUHPC better corrosion resistance. The mechanical properties of SSUHPC were slightly poor due to the uneven dispersion of steel fibers and air pores, with an- air pore porosity of 1.52% (above 200 μm) that was twice that of FRUHPC (0.6%). In this paper, the mechanics and anticorrosion performance of ultra-high-performance polymer cement mortar prepared with seawater sea sand were comprehensively evaluated, and the mechanism of performance difference between SSUHPC and FRUHPC was revealed, conducive to the targeted improvement of sea sand concrete.

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.

Biomineralization Induced by Cells of Sporosarcina pasteurii: Mechanisms, Applications and Challenges

Biomineralization has emerged as a novel and eco-friendly technology for artificial mineral formation utilizing the metabolism of organisms. Due to its highly efficient urea degradation ability, Sporosarcina pasteurii(S. pasteurii) is arguably the most widely investigated organism in ureolytic biomineralization studies, with wide potential application in construction and environmental protection. In emerging, large-scale commercial engineering applications, attention was also paid to practical challenges and issues. In this review, we summarize the features of S. pasteurii cells contributing to the biomineralization reaction, aiming to reveal the mechanism of artificial mineral formation catalyzed by bacterial cells. Progress in the application of this technology in construction and environmental protection is discussed separately. Furthermore, the urgent challenges and issues in large-scale application are also discussed, along with potential solutions. We aim to offer new ideas to researchers working on the mechanisms, applications and challenges of biomineralization.