Application Potential of Lysinibacillus sp. UA7 for the Remediation of Cadmium Pollution

Background: Cadmium (Cd) pollution poses a significant environmental challenge. Microbially induced carbonate precipitation (MICP), an advanced bioremediation approach, relies on the co-precipitation of soluble metals with the microbial hydrolysate from urea. This study isolated a urease-producing strain and evaluated its Cd remediation potential. Methods: The isolated strain UA7 was identified through 16S rDNA gene sequencing. Urease production was enhanced by optimizing the culture conditions, including temperature, dissolved oxygen levels—which were affected by the rotational speed and the design of the Erlenmeyer flask, and the concentration of urea added. Its Cd remediation efficacy was assessed both in water and soil. Results: UA7 was identified as Lysinibacillus sp., achieving peak urease activity of 188 U/mL. The immobilization rates of soluble Cd reached as high as 99.61% and 63.37%, respectively, at initial concentrations of 2000 mg/L in water and 50 mg/kg in soil. The mechanism of Cd immobilization by strain UA7 via MICP was confirmed by the microstructure of the immobilized products with attached bacteria, characteristic absorption peaks, and the formed compound Ca0.67Cd0.33CO3, which were analyzed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The Cd-remediation effect of strain UA7, which reduces lodging in wheat plants, prevents the thinning and yellowing of stems and leaves, and hinders the transition of soluble Cd to the above-ground parts of the plant, was also demonstrated in a pot experiment. Conclusions: Therefore, Lysinibacillus sp. UA7 exhibited high potential for efficiently remediating contaminated Cd.