Thermophiles in nanosized biocalcification: a novel approach for heavy metal remediation

Bio deposition of minerals is a prevalent occurrence in the biological realm, facilitated by various organisms such as bacteria, fungi, protists, and plants. Calcium carbonate is one such mineral that precipitates naturally as a consequence of microbial metabolic processes. This study investigates an innovative approach for MICP- mediated heavy metal remediation, carbon dioxide (CO₂) sequestration by utilizing thermophilic microorganisms isolated from such geographical area which is not yet been subjected to any systematic scientific study. Beyond the well-established urea hydrolysis pathway, this research highlights the contribution of non-ureolytic MICP mechanisms driven by the oxidation of organic compounds within the bacterial extracellular polymeric substances and cell wall components of Bacillus licheniformis. Notably, both strains of Bacillus licheniformis redirect its great potential towards biocalcification yielding 89.36 ± 1.8, 88.21 ± 1.5 mg CaCO₃ cells/ml and 90% efficiency for heavy metal remediation with the formation of nanosized (35.85 nm, 38.58 nm) biominerals. The influence of various parameters, such as temperature, pH, incubation time, CO₂ concentration, and calcium concentration on maximum CaCO₃ biosynthesis was evaluated. FTIR, XRD, and SEM-EDX analyses confirmed characteristic peaks for both calcite and vaterite polymorphs, consistent with these Pb incorporation into the mineral structure, rather than surface adsorption is observed. These comparative findings provide valuable insights for promising bioremediation approach for the sustainable, eco-friendly, energy-efficient immobilization of metal contaminants and bio-based carbonate production for efficient CO₂ sequestration.