Paenibacillus mucilaginosus-induced CO2 fixation into amorphous and crystalline carbonate minerals

Biomineralization offers a potential solution to CO₂ fixation during oil exploitation. This study investigates the pathways of CO₂ conversion and crystal nucleation mechanisms induced by Paenibacillus mucilaginosus ZH-28. At 16 % CO₂ (v/v), Carbonic Anhydrase (CA) activity produced by ZH-28 reached 156.68 ng/mL, promoting mineral deposition of 6.55 mg/mL, indicating potential for in-situ carbon fixation. The study reveals that biological acids promote amorphous calcium carbonate (ACC) precipitation, while high calcium ion concentrations accelerate ACC conversion to crystalline calcite. The thermogravimetric results showed that during the gradual transformation of ACC into calcite, large numbers of free cells and organic matter around ACC were encapsulated by the calcite. Molecular dynamics simulations verified that CA catalyzes CO₂ to HCO₃^- through a bicarbonate tetrahedral intermediate. The plugging potential of microbial-induced minerals was evaluated by microscopic displacement experiments and simulated core plugging experiment. Micro-morphological observations suggest that mineralization occurs via contact-mediated secondary nucleation, propagating in a zigzag pattern within 8–30 μm amorphous units. These findings provide insights into the transformation of amorphous materials into crystalline forms and offer new perspectives for CO₂-microbial enhanced oil recovery (MEOR).