Morphogenesis and evolution mechanisms of bacterially-induced struvite

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

Microbially induced calcium carbonate precipitation (MICP) is ubiquitous in the earth's lithosphere and brings the inspiration of bionic cementation technology. Over recent years, MICP has been proposed as a potential solution to address many environmental and engineering issues. However, the stability of cemented precipitations generated via MICP technology, especially the characteristics and change mechanism of crystal forms, is still unclear, which substantially hindered the understanding of biomineralization and prohibited the application and upscaling of MICP technology. Here, Sporosarcina pasteurii was selected as a model microbe to induce calcium carbonate mineralization in a series of standard nutrient solutions. The authors studied the process of precipitation from amorphous calcium carbonate to calcite crystal form and revealed the assembly behavior and mechanism of precipitations by FTIR, SEM, TEM and EDS. In the two crystal forms of induced calcium carbonate, the relative position and content of C, O, N, P and Ca elements were only slightly different. The molecular attachment and structural match of organic matrix made the crystals form change. Finally, a self-assembly theory was proposed to MICP, and it provided a solid theoretical basis for the technical specification of MICP technology in engineering application. KEY POINTS: • Organic matrix is intensively involved in MICP by forming functional groups. • Molecular attachment and structural match cause calcite crystal evolution. • A self-assembly theory is proposed for MICP.

Sustainable bio-bricks prepared with synthetic urine enabled by biomineralization reactions

In this study, mineralization during brick preparation was performed with ureolytic bacterium, Lysinibacillus fusiformis that use urine as a substrate, omitting the heat that is normally required. Artificial urine for reasons of standardization was used to grow the bacterium for bio-bricks made of clay and cement, but their mineralization was enabled by biological activity instead of by heat. Scanning electron microscopy and energy dispersion X-ray spectroscopy were conducted to analyse the microstructures formed by L. fusiformis that precipitated various minerals in synthetic urine. The brick specimens were tested for compressive strength that was 59% more than control ones, whereas porosity of bio-bricks was 13% compared to 22% of control specimens. The minerals formed in the bio-bricks confirmed as struvite, apatite and calcite by Fourier-transform infrared spectroscopy and X-ray diffraction spectra, were responsible for improved strength and reduced porosity. The research provided evidence in utilizing ureolytic bacteria as a mode to mineralize clay in brick production with the use of (artificial) urine as a substrate.