Effects and mechanisms of urease-producing bacteria mineralization on remediation of Cd- and Pb-contaminated soil

In order to repair heavy metal contaminated soil and ensure the quality and safety of vegetables, the urease-producing bacteria were screened from the vegetable rhizosphere soil by urease-producing medium. The adsorption and immobilization of Cd and Pb by functional strains were studied. Effects of functional strains on the growth and absorption of Cd and Pb by different vegetables were also studied by hydroponic experiment. Ten urease-producing bacteria were isolated from the rhizosphere soil of lettuce. Two strains, Microbacterium foliorum CH6 and Bacillus thuringiensis N3, showed highly ability to producte urease (62.6 and 59.6 (mS/(cm∙min), respectively) and immobilize Cd and Pb (84.6%~91.3%). SEM-EDS, FITR and X-ray showed that CH6and N3reduced the content of Cd and Pb in the solution through cell wall adsorption and induced precipitation. Soil static test showed that strains CH6 and N3 reduced the exchangeable contents of Cd and Pb (46.3%~66.7%) and increased the carbonate bound and residual fraction contents of Cd and Pb (40%~95.4%) in soil. A hydroponic experiment showed that, strains CH6 and N3 significantly reduced the Cd (39.2%~81.4%) and Pb (27.4%~82.4%) contents in the edible parts of lettuce, Chinese cabbage and Ipomoea aquatic. Urease-producing bacteria CH6 and N3 could mineralize CD and Pb in soil, reduce the content of available heavy metals in soil, and inhibit the absorption of Cd and Pb by lettuce, Shanghai green and cabbage. © 2020, Editorial Board of China Environmental Science. All right reserved.