Extracellular urease from Arthrobacter sp. strain 169 for enzyme-induced calcium carbonate precipitation (EICP) applications

Abstract Background Enzyme-induced carbonate precipitation (EICP) is a process that promotes calcite formation via urease-mediated hydrolysis of urea, resulting in carbonate ion production in the presence of calcium. This study aimed to isolate and characterize an extracellular urease-producing Arthrobacter species with high enzymatic activity and efficient calcite precipitation capability. Based on the determined maximum reaction rate (V max ) and Michaelis-Menten constant (K m ) values, the optimal substrate concentration for urease activity was established. Results The bacterium isolated from agricultural soil exhibited the highest extracellular urease activity. Based on 16 S rRNA gene sequencing and metabolic and physiological profiling, the isolate was taxonomically identified as Arthrobacter sp. strain 169. Semi-quantitative XRD analysis showed that calcium carbonate precipitated from extracellular urease activity in the cell-free supernatant. The composition consisted of 96.6% calcite and 3.4% vaterite. In contrast, calcite precipitated directly in the bacterial culture medium contained 88.7% calcite and 11.3% vaterite. Urease activity, measured by ammonium production and expressed in enzyme units, indicated that isolate 169 exhibited the highest activity of 4.34 U/mL. Kinetic analysis of the extracellular urease, based on the Michaelis-Menten model, showed a V max of 8.11 U/mL and a K m of 237 mM. The enzyme exhibited optimal activity at pH 7.4 and 40 °C, with half-lives of 35 h at room temperature and 40 h at 4 °C. Conclusions Carbonate precipitation using extracellular urease, rather than living microbial cells, enables deeper penetration into fine-grained soils where conventional microbially induced carbonate precipitation (MICP) may be ineffective. Moreover, the extracellular urease produced by Arthrobacter sp. strain 169 offers a practical and scalable alternative to plant-derived urease for industrial applications.