Optimization Of Soil Lead Pollution By Phosphorus - Solubilizing Bacteria And Its Mechanism

Along of lots of coal, petroleum and natural gas are massive mining, large heavy metals associated with them migrate with acidic mine water to surrounding soil. Lead arranges the third in the heavy mental toxic table, lead is one of pollution elements which are highly toxic and non essential for plants, animals and human. The heavy mental in soil could affect human health through the food chain. In this study, two strains of phosphate-solubilizing bacteria were isolated from lead polluted soil. The bacteria have high ability of dissolve phosphorus and could tolerate high Pb concentration, then using Response Surface Methodology we optimized the best condition of lead immobilization by phosphate-solubilizing bacteria. Pot experiment was explored to test the effect of lead immobilization by phosphate-solubilizing bacteria.Research on two phosphate-solubilizing bacteria with high ability of dissolve phosphorus and could tolerate high Pb concentration indicating that the ability of dissolve inorganic phosphorus of ID-a was1020mg/kg, dissolve organic phosphorus was130mg/kg, dissolve calcium phytic acid was940mg/kg, and to strain3-5-1-1,the ability of dissolve inorganic phosphorus was1030mg/kg, dissolve organic phosphorus was135mg/kg, dissolve calcium phytic acid was800mg/kg. Two phosphate-solubilizing bacteria could grow better when Pb concentration is800mg/kg, it meant that they could tolerate high levels of lead; Through the study of physiological and biochemical characteristics of two strains came out that they present Gram-negative; The growth curve indicated the logarithmic phase of two strain is10-20h、the stable phase is20-80h and after80h they entered decline phase. By study two strains’ content of IAA and siderophore, it demonstrated that the content of IAA of ID-a is45.07μg/mL and content of siderophore is0.58, compared with ID-a, content of IAA of3-5-1-1was23.92μg/mL content of siderophore is0.64;3-5-1-1was identified as Pseudomonas vranovensis and ID-a was identified as Enterobacter agglomerans by the method of16S rRNA sequencing.In this study, the Response Surface Methodolog was applied in optimizing the situation for lead immobilization, five factors(moisture, temperature, TOC, Cl-, pH) which haven significant effects on lead immobilization rate were chosen for the optimization. For the five significant factors, a three-level five-factor Box-Behnken design experiment with46runs was employed, and a quadratic regression model about lead immobilization rate by phosphate-solubilizing bacteria were fitting by RSM.Y=52.92-0.12A+0.75B-2.83C+0.32D+6.89E-6.37AB-1.67AC+1.66AD+0.18AE-1.80BC+1.17BD-2.10BE-4.61CD-7.66CE+3.43DE-10.54A2-10.12B2-17.45C2-18.00D2+5.66E2。 The best lead immobilization conditions and maximum lead immobilization rate were test by analysis of variance (ANOVA). The optimal situation for lead immobilization was:moisture5.33g/kg, temperature22.14℃,TOC803.91mg/kg, Cl3610.93mg/kg, pH6,and the maximum lead immobilization rate was67.4588%.The results of the pot experiment demonstrated that the grew of plants were inhibited with the increase of lead concentration and the plants inoculated phosphate solubilizing bacteria ID-a and3-5-1-1had the maximum biomass and the lowest lead concentration in leaves. The plants inoculate phosphate solubilizing bacteria grew much better than the others, the sequence was A(inoculated ID-a)>B(inoculated3-5-1-1)>C(inoculated phosphate fertilizer)>CK. The lead contention in plants under ground increased at first then reduced and at last increase slowly, and the same to the plants above ground, while had the opposite sequence:CK> C(inoculated phosphate fertilizer)>(inoculated3-5-1-1)> A(inoculated ID-a). The phosphate solubilizing bacteria could release the phosphate radical from the soil, then the phosphate radical formed lead phosphate precipitation by combining with the Pb2+in the soil, as to immobilized the lead exited in soil. At the same time, phosphate solubilizing bacteria ID-a and3-5-1-1could release secretions such as IAA and siderophore which might promote the growth and development of plants in a certain extent.In conclusion, inoculated phosphate solubilizing bacteria to lead polluted soil can not only suppressed the absorption of lead in plants effectively also promoted the plants to absorb nutrients, that not only achieved the purpose of remediation while production but also improved the yield and quality of crops, so has good ecological benefits and economic benefits.