Bacterial attachment by crystal in MICP

Microbially induced calcium carbonate precipitation (MICP) is recognized as a promising technique for soil improvement. The morphological evolution of calcium carbonate (CaCO3) crystals during the MICP process significantly impacts the engineering properties of biocemented soils. However, the morphological changes of CaCO3 precipitates upon bacterial adsorption onto crystal surfaces have not been sufficiently studied. This study employs real-time laser scanning confocal microscopy (LSCM) to simultaneously monitor the dynamics of CaCO3 growth and bacterial attachment during the MICP process, while fluorescence staining is used to differentiate between living and dead bacteria. The results indicate that during the initial stage of the MICP process, the predominant morphology of the CaCO3 crystals was elliptical, with a minor fraction exhibiting a rhombohedral morphology. Over time, additional elliptical crystals gradually formed around the existing elliptical ones. As the crystals grew, certain bacteria in the vicinity of the crystals became adsorbed onto their surfaces, irrespective of bacterial viability. However, bacterial adsorption did not alter the morphology of the crystals. The study provides microscale insights into the mechanisms of bacterial attachment to CaCO3 crystals during biomineralization.