Remediation Of Nickel And Cadmium Contaminated Soil By Indole-acetic Acid Producing Bacteria

In recent years,the safety production of Ni and Cd contaminated cultivated soil has been widely concerned by people.Due to the advantages of low cost and environmental friendliness,the potential of microbial remediation in the field of heavy metal pollution has been paid more and more attention.Based on Ni and Cd pollution of farmland soil production safety as the goal,a strain were isolated by indoleacetic acid(IAA),further studies the IAA bacteria production characteristics and the response characteristics of Ni²⁺and Cd²⁺,and Comamonas testosteroni ZG2 biochar bacterium repairing effect of Ni and Cd contaminated soil,the main results were as follows:(1)A strain of Bacillus safensis,named N4,resistant to Ni and Cd,was isolated from contaminated soil.The strain N4 had strong resistance to Ni²⁺and Cd²⁺.Although the growth of strain N4 was affected at 800 mg·L^-1 and 50 mg·L^-1,the OD₆₀₀ of fermentation broth could still reach 1.422 and 0.413,respectively.The amount of IAA produced by strain N4 was as high as87.84 mg·L^-1,and the amount of IAA decreased gradually with the increase of Ni²⁺concentration.However,when the concentration of Ni²⁺reached 800 mg·L^-1,the content of IAA still reached 34.37 mg·L^-1.With the increase of Cd²⁺concentration,the yield of IAA first increased and then decreased.When the concentration of Cd²⁺was 10 mg·L^-1,the highest content of IAA was 87.13 mg·L^-1,and when the concentration of Cd²⁺was 50 mg·L^-1,the yield of IAA still reached 18.96 mg·L^-1.In addition,strain N4 could significantly increase plant height,root length,fresh weight and dry weight of Chinese cabbage when remediation of Ni and Cd contaminated soil by single strain N4.Moreover,it could decrease the Ni content in aboveground parts of Chinese cabbage,but increase the Cd content in aboveground parts of Chinese cabbage.(2)Strain N4 can be symbiotic with Comamonas testosteroni ZG2,and the cell number ratio of the two is about 9:1.Compared with strain N4,the resistance of the compound strain to Cd²⁺was significantly enhanced.When the concentration of Cd²⁺was 50 mg·L^-1,the OD₆₀₀ of the fermentation broth could still reach 0.532,but the resistance of the compound strain to Ni²⁺had no obvious change.With the increase of Ni²⁺concentration,the production of IAA in the composite strain decreased gradually,but with the increase of Cd²⁺concentration,the production of IAA increased first and then decreased,which was consistent with the trend of IAA production in the single strain N4.However,the effect of Ni²⁺and Cd²⁺on the composite strain was less than that of the single strain N4.The resting and growing cells of both strains N4and ZG2 could attach to the surface of biochar,which not only maintained their ability to produce IAA,but also reduced the influence of Ni²⁺and Cd²⁺on the morphology of biochar.Biochar could enhance the remediation effect of single strain and compound bacteria.The plant height,root length and fresh weight of Chinese cabbage were increased by 93.46%,32.74%and 4.60 times compared with the control without treatment after the combination of compound bacteria and biochar to remediation of Ni and Cd contaminated soil,respectively.The contents of available Ni and Cd in the soil decreased by 47.75%and 52.95%,respectively.The contents of Ni and Cd in the ground of Chinese cabbage were reduced to 0.22mg·L^-1 and0.15mg·L^-1,which met the food safety standards and met the safety production requirements of Ni and Cd contaminated soil.The above results indicated that the N4 isolates of the Ni and Cd resistant Bacillus indole-producing bacteria obtained in this study not only had strong resistance to Ni²⁺and Cd²⁺,but also maintained good IAA production ability under the influence of higher concentration of Ni²⁺and Cd²⁺.In addition,strain N4 had an obvious symbiotic relationship with Comamonas testosteroni ZG2,and the resistance to Ni²⁺and Cd²⁺was significantly enhanced in the co-culture process.The combined restoration of Ni and Cd contaminated soil by composite bacteria and biochar promoted the growth of Chinese cabbage,and the content of Ni and Cd in the aboveground of Chinese cabbage also reached the food safety standard.These results provide excellent strain resources,theoretical basis and technical support for remediation of Ni and Cd soil with indole-acetic acid-producing bacteria.