Isolating and Using Bacteria, Producing Urease and L-asparaginase, and Effective on Calcium Carbonate Bioproduction to Remove Zinc from Contaminated Solutions

Heavy metal pollution in soil and water resources has become a serious problem not only in the production of healthy agricultural products, but also in the ecosystem health. Microbially induced calciumcarbonate precipitation (MICP) is a low-cost and environmentally friendly methods for reducing water resources and soil pollution. The aim of this study was to isolate native and efficient bacteria in the biological production of calciumcarbonate in order to remove zinc from contaminated solution. Isolating and screening native bacteria, producing urease and L-asparaginase, was accomplished.  Then, the changes in ammonia, pH and electrical conductivity (EC), as well as removal of zinc from the contaminated solutions were studied using these two efficient isolated bacteria in the presence of sporocarsina pasteurii. The results showed that in the presence of all three bacteria, the amount of produced ammonia, pH and EC in the culture media increased significantly compared to the ones in the control (without bacterial inoculation) (p < /em>≤0.05). The efficiency of isolated urease-producing strain in removal of zinc from the contaminated solution was almost equal to that of sporosarcina pasteurii, while the efficiency of isolated L-asparaginase-producing strain was more. Sporosarsina pasteurii removed 51.32, 65.94 and 70.36% and urease producing strain removed 65.49, 68.07, and 71.46 of zinc in the solutions containing 0.5, 2 and 4 mM Zn, respectively. However, L-asparaginase-producing strain removed 96.29, 93.88, 97.06 and 97.32% of zinc in solution containing 0.5, 2, 4 and 8 mM Zn, respectively. Therefore, it seems native urease- and L-asparaginase-producing bacteria can be useful and efficient in Zn bioremediation of contaminated solutions by MICP process.