Bacterial attachment by crystal in MICP

Abstract

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.

Keywords

MICP / Confocal microscopy / Calcium carbonate / Mineral morphology / Bacteria

CRediT authorship contribution statement

Hanlong Liu: Conceptualization, Writing - review & editing, Supervision. Jinxuan Zhang: Investigation, Methodology, Writing - original draft. Yang Xiao: Writing - review & editing, Conceptualization, Funding acquisition. Xiang He: Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Hanlong Liu is the Editor-in-Chief of Biogeotechnics, Yang Xiao is Executive Deputy Editor-in-Chief of Biogeotechnics, they were not involved in the editorial review or the decision to publish this article.

Acknowledgements

We would like to express our gratitude to the Research Microscope Systems Division of Carl Zeiss (Shanghai) Management Co., Ltd. for generously providing the figures and movies used in this paper. Mr. Liang Yuan, as a sales engineer, facilitated the coordination of this experiment, while Mr. Yuan Zhuang, as a senior application specialist, conducted the experimental operations with the laser scanning confocal microscopy measurements. We would also like to thank the dedicated staff at Carl Zeiss for their support and contributions to this study.

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