A highly effective strain screened from soil and applied in cementing fine sand based on MICP-bonding technology

Soil cementation based on microbially induced calcite precipitation (MICP) technology is a new research hotspot in the field of biogeotechnical engineering. However, due to the presence of only calcium bonds among particles, MICP-cemented soil shows obvious brittleness, which is the bottleneck of the application of MICP technology in geotechnical engineering. MICP-bonding technology can improve the shortcoming of high brittleness of the calcium bond by increasing the plastic bond among matrix particles. Based on MICP-bonding technology, this study isolated a high-efficiency strain named XR1#, which has the ability to produce both urease and extra cellular polysaccharide. Gene sequencing identified the strain as Bacillus oceanicus. The superiority of XR1(#) bacteria is its ability to induce mineralization and polysaccharide production at the same time. Through the combination of calcium carbonate crystal filling and extracellular polysaccharide bonding, the strength and ductility of the sand column were improved, and the brittle characteristics of traditional MICP technology were reduced. By studying the effect of nutrient elements of the culture medium on calcium precipitation and polysaccharide yield, the two metabolites of XR1# bacteria could be artificially regulated. In an experiment with microbial-cemented fine sand, compared with the traditional Sporosarcina pasteurii, XR1#-cemented sand columns had high production and uniform distribution of calcium carbonate, high strength, and good ductility, and showed obvious advantages. This study provides a new strain with high efficiency and multiple functions for MICP-bonding technology and a new research idea for reducing MICP brittleness.

Automated summary

Soil cementation based on microbially induced calcite precipitation (MICP) technology is a hot research topic in biogeotechnical engineering. The brittleness of MICP-cemented soil, caused by only calcium bonds among particles, limits the application of MICP technology. However, MICP-bonding technology can overcome this issue by increasing the plastic bond among matrix particles. In this study, a high-efficiency strain, named XR1#, was isolated and identified as Bacillus oceanicus. The strain has the ability to induce mineralization and produce polysaccharides simultaneously. By combining calcium carbonate crystal filling and extracellular polysaccharide bonding, the strength and ductility of the sand column were improved, reducing the brittleness of traditional MICP technology. Additionally, the metabolites of the XR1# bacteria could be artificially regulated by studying the effect of nutrient elements. Microbial-cemented fine sand columns using XR1# showed advantages over traditional Sporosarcina pasteurii, including high production and uniform distribution of calcium carbonate, high strength, and good ductility. This study provides a new strain and research idea for MICP-bonding technology to reduce brittleness.