| China is a big country of non-ferrous metal production and consumption,where the environmental and ecological security seriously threatened by heavy metal pollution caused by non-ferrous metal smelting process,especially for the surrounding farmland soil.It makes the soil biodiversity deterioration,fertility decline and compaction serious,resulting in huge losses of food and crops,which has become an urgent problem to be solved in modern agriculture.Microbial immobilization is a novel and environmentally friendly technology that microorganisms are used to reduce metal availability in soil and accumulation of heavy metals in plants,which can effectively solve the problem of heavy metal pollution in farmland soil.In this study,three urease-producing microorganisms were screened out from heavy metal contaminated farmland soil around non-ferrous mining and metallurgy park in Guangxi,and their growth characteristics were studied,while the optimal carbon source in the culture system was determined.Meanwhile,the effects of affecting factor including temperature,pH value,urea concentration and inoculation amount on Cd and Pb solidified by microorganism were investigated.The mechanism of heavy metals Cd and Pb in the solidified solution was analyzed by FTIR,SEM-EDS and XRD.Pot experiments were carried out to explore the affect of biomass and Cd and Pb adsorption rates of urease producing bacteria on pakchoi grown in contaminated soil,and bioinformatics methods such as high-throughput sequencing and metagenomics were used to analyze the changes of microbial population structure during the curing process.The main contents and results are as follows:Three strains with high urease-producing activity CSS-2,CSS-7 and CSS-16 were screened,which were identified as Bacillus sp.,Bacillus Megaterium and Bacillus Aryabhattai,and their urease activities were 677 U/mL,663 U/mL and 683 U/mL,respectively,while the maximum tolerated concentrations of Cd and Pb are 50 mg/L and 250 mg/L,respectively.In the culture system with glucose as carbon source,the urease activity of the mixed bacteria could reach 2269 U/mL.The optimum conditions for urease-producing microorganisms to solidify heavy metals Cd and Pb were determined as follows:temperature 25?,pH 7.0,urea concentration 20 g/L and inoculation amount 20%.Under the optimum solidification conditions,the solidification rates of Cd and Pb are 84.65%and 97.93%,respectively,the pH value of the system reached 9.30.The mechanism of heavy metal Cd and Pb solidified by urease bacteria was proved.FTIR analysis showed that the amide compounds,lipids,proteins and polysaccharides on the surface of urease bacteria were involved in the adsorption of Cd and Pb.TEM-EDS results showed that the effect of microorganisms on Cd and Pb was mainly concentrated in the cell,followed by cell wall,and finally extracellular.The results of SEM-EDS and XRD showed that the precipitation products were mainly CdCO3?PbCO3 and co-precipitation product Ca0.67Cd0.33CO3.The results of urease-producing bacteria on the biomass and Cd and Pb adsorption of pakchoi in heavy metal contaminated soil showed that compared with the control group,the edible part length of pakchoi in the repair group increased by 19.95%,and the Cd and Pb contents decreased by 10.42%and 33.33%,respectively.The available Cd and Pb in the soil decreased significantly,and the curing rates were 25.29%and 30.30%,respectively.Conclusion,the screened urease-producing bacteria had good solidification effect on Cd and Pb,and had certain promoting effect on crops and inhibiting heavy metal absorption. |
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