A genetic approach was proposed to modify the characteristics of Bacillus subtilis strain WB800 (B. subtilis WB800) for self-healing of concrete cracks. Three genes, namely gerAa which encodes germination receptors activated by L-alanine, tupA which is responsible for the synthesis of teichuronopeptide, and ca which encodes carbonic anhydrase (CA) catalyzing the synthesis of carbonate ion, were separately transformed into WB800. To protect bacterial cells from being squeezed, microspheres were produced with microcrystal cellulose (MCC) before the introduction of bacteria into the specimens. The results showed that the modified B. subtilis expressing GerA achieved 39.9% of germination ratio compared to 17% by the original host cells. With the transformation of tupA, the modified strain demonstrated higher resistance to alkaline environments, tolerating pH as high as 11, while the original strain only tolerated pH 9. The modified strain expressing CA induced more calcium carbonate than the original cells. Energy dispersive spectroscopy (EDS) identified the produced precipitate to be calcite (CaCO₃). Moreover, a mathematical model was developed to optimize the influential factors of calcium precipitation process. Finally, based on the above results, an effective self-healing of concrete crack was achieved. This study may provide a promising strategy to improve the efficiency of bacterial self-healing of concrete cracks.

Keywords: Bacterial spores, Gene modification, Self-healing, Concrete crack, Modeling