Microbially induced calcium carbonate precipitation (MICP) represents a pivotal biogeochemical process for inorganic carbon sequestration in karst ecosystems. In this study, metagenomic sequencing was used to analyze the microbial communities on stalagmite surfaces in two caves in Guizhou Province, and mineralizing bacteria were then isolated for MICP simulation experiments. We measured bacterial pH levels and carbonic anhydrase (CA) activity; characterized the precipitated minerals using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and Fourier transform infrared (FTIR) spectroscopy; and determined the total carbon content to calculate the sequestration efficiency. The results revealed highly similar microbial communities between the two caves, with mineralizing bacteria primarily belonging to Pseudomonadota, Actinomycetota, and Firmicutes. Functional assays demonstrate a dual mechanism underlying bacterial precipitation: carbonic anhydrase (CA) activity speeds up CO2 hydration, while metabolic alkalization (final pH >9.0) raises the saturation index. Biotic mediation induces the formation of high-crystallinity calcite and metastable vaterite, distinct from the exclusively calcite phase observed in abiotic controls, which might be because extracellular polymeric substances (EPS) serve as nucleation templates, lowering the thermodynamic energy barrier for precipitation. Compared with abiotic processes, bacterially induced precipitation significantly increases carbon sequestration, in which the strains Arthrobacter kerguelensis DFS-17, Bacillus licheniformis SW-18, and Peribacillus frigoritolerans DFS-15 demonstrate, with the strain Arthrobacter kerguelensis DFS-17 achieving a maximal carbon sequestration efficiency (CSE) of 18.5%. These results elucidate the active role of cave microorganisms in regulating carbonate polymorph selection and enhancing the stability of the karst carbon sink.
Yu et al. (Wed,) studied this question.