Exploring Of The Mechenisms Of Bioremedation Of Lead Contaminated Soil And Optimization By Phosphate Solubilizing Bacteria(PSB)

The remediation of heavy metal contaminated soil is of great significance to improve crop yield and safety.In this study,two strains of phosphate-solubilizing ability with high efficiency of dissolving phosphorus and resistance to lead growth were isolated from the tailings soil of lead-zinc concentrator.The effects of two strains of phosphate-solubilizing bacteria on soil lead pollution were studied by pot experiment.The effects of phosphorus and phosphorus on the soil were studied.The results showed that the phosphate treatment ability of strain KMC-7a-2 reached the maximum value of 256.73mg/L on the eighth day,and the medium pH was 3.98.The phospholytic capacity of strain 4-5a-1 reached the maximum value of 49.59mg/L on the sixth day,and the pH value of the medium was 8.98.The results showed that strain KMC-7a-2 had the better phosphate-dissolving capacity than 4-5a-1 in different testing time.The correlation between phosphate solubilization capacity and pH by strain KMC-7a-2 was significant salience(P=0.004<0.01),4-5a-1 was not significant(P>0.05).KMC-7a-2 was identified as Pseudomonas gessardii and 4-5a-1 was identified as Stenotrophomonas maltophilia by the method of 16SrRNA sequencing.A pot experiment was conducted to evaluate the effect.It showed that the phosphate-solubilizing bacteria can significantly reduce the exchangeable Pb and bound to carbonate Pb in the soil.The sequence was CK(control group)>C(add Ca3PO4)>A(add KMC-7a-2)/B(add 4-5a-1).SEM analysis revealed that HP?CIP and PH could be formed after stabilization in the group A8 and B8.Compared with group CK,A and B could effectively increase the soil catalase,urease,protease acid and alkaline phosphatase activity in the soil.The addition of heavy metal Pb to the soils of the inorganic phosphorus strain and the protective effect on the soil sucrase,acid phosphatase and catalase were relatively strong.The addition of heavy metal Pb to the soil urease and alkaline phosphatase was higher in group B of organophosphate strain.Compared with CK group,the percentage of chlorophyll increased from group A,B and C was 9.09%?54.36%,10.96%?47.26%and 3.21%?16.07%,respectively.The percentage of plant catalase activity increased from 4.40%to 22.04%,5.94%?29.12%and 0.00%?2.52%,respectively.The percentage of plant peroxidase activity increased 9.90%?133.35%,11.30%?130.64%and 0.00%?14.33%.The size of the green vegetables chlorophyll content sequence was:A>B>C>CK.With the increase of lead levels in the soil,the green chlorophyll,catalase and peroxidase showed increased after the first reduce the changing trends.The peroxidase activity reached the highest at the soil lead levels of 600 mg/kg.The green plant biomass showed a trend of fluctuations.The sequence in stem and leaf wet weight and dry weight of plant sequence was:B/A>C>CK.The sequence of root part of lead concentration by oilseed rape was:A>CK>C>B.When the soil lead concentration of 0?1200 mg/kg,The sequence of the content of Pb in the stems and leaves by oilseed rape was:CK>C>A>B.When the soil lead concentration of 1200-2100mg/kg,The sequence of the content of Pb in the stems and leaves by oilseed rape was:CK>C>B>A.Under the conditions of pH 6.0,adsorption time 5d,and initial bacterial amount 2.0%,the rates of removing Pb2+ by the strain KMC-7a-2 reached 97.15%.Under the conditions of pH 7.0,adsorption time 3d and initial bacterial amount 1.0%,the rates of removing Pb2+by the strain 4-5a-1 reached 95.95%.When the Pb2+ concentration was 200mg/L,strain KMC-7a-2 culture medium of Pb2+ precipitation effect was good,the removal rate reached 92.56%.Strain KMC-7a-2 bacterium has biosorption ratio(92.56%)to 400mg/L lead cation and the adsorption effect was better.when Pb2+ concentration was 200mg/L and 400mg/L,strain 4-5a-1 bacterium to 200mg/L and 400mg/L lead cation was better than culture medium.The combination of adsorption and precipitation of heavy metal Pb was better than that of microorganism alone.Under the conditions of pH 6.0,the stability of the precipitation of Strains KMC-7a-2 and 4-5-a-1 were better.Indicating that the use of microbial precipitation than the use of its separate adsorption effect better.XRD patterns of the deposit by culture medium of strain KMC-7a-2 were analyzed.It was found that lead immobilization was attribute to the P-induced formation of pyromorphite like compounds[Pb5(PO4)3Cl,CIP]?[PbHPO4,HP]and[Pb3(PO4)2,Pb-P].XRD patterns of the deposit by culture medium of strain 4-5a-1 were analyzed.It was found that lead immobilization was attribute to the P-induced formation of pyromorphite like compounds[Pb3(PO4)2,Pb-P]and[Pb10(PO4)6(OH)2,PH].The results could be used for optimizing bioremediation techniche and increasing safety and yields of crops,providing the theory basis for improvement of bioremediation of heavy metal contaminated soil.