Effects of nitrogen sources on MICP-related metabolic mechanism of Sporosarcina pasteurii and soil reinforcement

Sporosarcina pasteurii (S. pasteurii) is widely used in microbial-induced carbonate precipitation (MICP) due to its high urease activity. In this paper, the effects of nutrients on the metabolic mechanism and mineralization ability of S. pasteurii were studied by comparing the bacteria's growth, gene expression, and mineralized sand column under different nitrogen sources. The results showed that urea and soy peptone replacing the inorganic and organic nitrogen sources in ammonium sulfate-yeast extract (NH4-YE) medium can increase the urease activity of S. pasteurii by 11.43% and 17.10%, respectively. In the composite nitrogen source medium composed of urea and soy peptone, the urease activity of S. pasteurii increased by 25.30%. The transcriptome sequencing results showed that the modified medium of urea and soy peptone could promote the basic life activity and metabolism of S. pasteurii and is beneficial to urease expression. Among them, the gene difference between the modified urea medium and the primary medium was more obvious, and the urea medium could promote the ATP synthase related to urease expression and urea hydrolysis. The unconfined compressive strength (UCS) of sand columns reinforced with S. pasteurii cultured in Urea-YE, NH4-Soy peptone and Urea-Soy peptone increased by 27.6%, 36% and 58.1% respectively. The permeability decreased by 14.8%, 20.1% and 81.3% respectively compared with that of sand columns reinforced with S. pasteurii cultured in NH4-YE. The higher the urease activity of cultured bacteria, the more calcium carbonate produced after mineralization reaction. In addition, the urease activity of bacteria has an influence on the morphology of calcite crystals. This study can facilitate our understanding of optimizing the culture medium of S. pasteurii and the artificial regulation of urease activity in the process of MICP.