Rapid formation of CaCO₃/EPS hybrid coatings via microbially induced mineralization for corrosion-resistant steel

osion of steel in harsh environments presents significant challenges. Microbially influenced corrosion inhibition (MICI) has emerged as a sustainable solution. This study utilizes the ureolytic bacterium Sporosarcina pasteurii to construct a biomimetic organic–inorganic hybrid membrane on mild steel via in situ cell–CaCO₃ biomineralization. Upon immersion in bacterial culture and cementation solution, rapid precipitation of a dense CaCO₃/extracellular polymeric substances (EPS) membrane occurred. Structural characterization confirmed the formation of a compact, adherent biofilm–mineral layer. Electrochemical polarization tests showed a substantial reduction in corrosion current from 8.65 μA·cm⁻² (NC) to 0.01 μA·cm⁻², indicating strong corrosion inhibition. Even a 1-day pretreatment generated a stable barrier, whereas the non-mineralized EPS biofilm offered only temporary protection. Mechanistic studies revealed that EPS binds Fe²⁺ and Ca²⁺ while urease activity raises pH and produces carbonate, promoting calcite nucleation. The resulting CaCO₃/EPS hybrid coating impedes O₂ and Cl⁻ ingress and is sustained by microbial metabolism. This work demonstrates a rapid, eco-friendly strategy for forming durable bioinspired coatings with strong potential for scalable industrial deployment.