Research on microbially induced calcite precipitation (MICP) based on gene vector construction optimization technology for stone relic crack repair

Microbially induced calcite precipitation (MICP) holds great potential for repairing cracks in stone cultural relics, and enhancing urease activity can notably improve repair efficacy. This study optimized gene vector construction to achieve efficient expression of Bacillus pasteurii urease gene cluster in Bacillus subtilis , then tested the growth characteristics and urease activity of the original Bacillus pasteurii (Strain A) and recombinant Bacillus subtilis (Strain B), and determined their optimal cementation solution concentrations and bacteria-to-cementation ratios via component optimization. The technology was further applied to repair stone wall cracks at Kaifeng Zhouqiao Sites under optimal conditions. Results showed successful urease gene cluster expression in Strain B, which had 58.8% higher maximum OD 600 and 44.6% higher urease activity than Strain A. The optimal cementation solution concentrations were 1 mol/L (Strain A) and 1.5 mol/L (Strain B), with corresponding optimal bacteria-to-cementation ratios of 1:1 and 1:1.25; both strains achieved over 90% calcium carbonate generation rate within 2 h under these conditions. For 4 cm-wide cracked stone samples, Strains A and B restored 80%–90% of flexural strength; for 2 cm-wide cracks, Strain B increased strength by 20% while Strain A reduced it by 6%. SEM and XRD analyses revealed Strain B’s superior repair effect stemmed from its 44.6% higher urease activity and doubled calcite production relative to Strain A. This study expands the foundational applications of MICP technology in cultural heritage conservation.