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

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, CaCO3, and (Ca0.67, Cd0.33)CO3. Furthermore, Ca2+ could also protect ureolytic bacteria against toxicity from other heavy metals.The authors would like to thank the supports from the program of Jiangsu Distinguished Professor and the Innovation/Entrepreneurship Program of Jiangsu Province, Jiangsu Province Key Project of Research and Development Plan (BE2020676), the China Postdoctoral Science Foundation (2020M671359), Initial Research Fund of Highly Specialized Personnel from Jiangsu University (4111370003), Senior Talent Funded Projects of Jiangsu University (17JDG016), and Project of Faculty of Agricultural Equipment of Jiangsu University (NZXB20200209), and Natural Science Foundation of Jiangsu Province (Grant no. BK20200914)