Ca-mediated alleviation of Cd2+ induced toxicity and improved Cd2+ biomineralization by Sporosarcina pasteurii

Highlights: • Ca²⁺ supplement significantly alleviated toxicity of Cd²⁺ to Sporosarcina pasteurii. • Survivability and urease activity of S. pasteurii were improved with Ca²⁺ supplement. • Both low and high concentration of Cd²⁺ (0.1–50 mM) was bioremediated via MICP process. • Ca²⁺ could also protect S. pasteurii against Cu, Zn, Mn, and Ni stress. Microbial induced carbonate precipitation has been widely used in the biomineralization of heavy metals Cd²⁺. However, the low Cd-tolerance of ureolytic bacteria limits the applications with only low Cd²⁺concentrations. In this study, we discovered a simple approach to significantly enhance the Cd²⁺ resistance of ureolytic bacteria through an immediate supplement of Ca²⁺. The Ca²⁺ protected the cells by reducing the extracellular and intracellular Cd²⁺ concentration by about 50%. As a result, the Cd²⁺ removal efficiency was notably improved by about 100% (52.72% to 99.43%, Cd = 5 mM) with Ca²⁺ supplement. Moreover, extremely high concentration of Cd²⁺ could be almost completely removed (99.46% at C₀ = 20 mM and 99.60% at C₀ = 50 mM) within 24 h. Microstructure analyses indicated that the mineralized precipitates were rhombohedral-shaped CdCO₃, CaCO_3, and (Ca0.67, Cd0.33)CO₃. Furthermore, Ca²⁺ could also protect ureolytic bacteria against toxicity from other heavy metals.