Effects Of Plant Growth Promoting Bacteria Bacillus.sp YM-1 On Passivation For Pb And Growth-promotion For Rape

With the rapid development of industry,heavy metal polluted soil is increasingly serious,causing the environment and human health problems,which has aroused wide public concern.Plant growth promoting bacteria can not only stabilize heavy metal and alleviate heavy metal stress,also promote the growth of plants.The bioremediation based on Plant growth promoting bacteria is an effective remediation coupled with agro-production.In this study,we isolated the plant growth promoting bacteria Bacillus.sp YM-1 from rhizosphere soil and analyzed its heavy metal adsorption characteristics and growth-promoting characteristics.Immobilized YM-1 on mushroom residue carrier,through pot experiment,we studied the passivating effect for Pb in soil and growth-promoting mechanism for rape.The main results were as follows:1.Isolation and identification of the Pb-tolerant Plant growth promoting bacteriaThis study isolated a Pb-tolerant PGPB from rhizosphere soil,it is gram positive bacteria and normally grows on 500 mg·L^-11 Pb soild medium.Physiological,biochemical and 16S rDNA sequencing analysis showed that the bacteria was identified as Bacillus.sp and named as YM-1.2.Determination of heavy metal resistance and growth-promoting capacitiesThe minimum inhibition concentration of Pb、Zn、Cu by strainYM-1 was 500、800、400 mg·L^-1.Under the stress of Pb,Zn,Cu,YM-1 had better growth-promoting characteristics,which the maximum ACC was 1.194μmolα-ketobutyratemg^-1·h^-1,IAA was 66.29 mg·L^-1,siderophore production was 74.27%SU,phosphorus solubilizing capability was 26.88 mg·L^-1.Under different Pb concentration,seed germination rate after YM-1 soaked significantly increased from 6.82%to54.17%.3.The absorption property of strain YM-1 for Pb²⁺The optimum adsorption conditions of strain YM-1 for Pb²⁺was:pH 5.5,initial concentration of Pb²⁺100 mg·L^-1,bacteria concentration 1.5 g·L^-1,adsorption time 30 min.Under this condition,the maximum adsorption rate and adsorption quantity were 89.62%and 14.94 mg·L^-1.TEM and EDX analysis of YM-1 cells before and after the adsorption showed that cell was rod structure before adsorption and Pb absorption peak was not found.After the adsorption,the cell became irregular and a layer of black deposits adhered on the surface,there was a Pb absorption peak.4.Survival dynamic condition of YM-1and immobilized YM-1 in soilUsing immobilized technology,immobilized strain YM-1 on mushroom residue carrier.Then compared its survival dynamic condition with YM-1 in Pb-polluted soil.After 40 d,the viable count of immobilized YM-1 was 8.42×10⁶ cfu per gram of soil,while the viable count of YM-1was reduced to 9.52×10² cfu per gram of soil.5.Effects of YM-1and immobilized YM-1 on effective state Pb and soil physicochemical propertiesTessier continuous extraction method analyzed Pb speciation in soil.The results were that compared with control,YM-1 treatment,mushroom residue treatment,YM-1+mushroom residue treatment,immobilized YM-1 treatment all decreased the contents of exchangeable Pb,declined by12.61%-27.09%,14.86%-32.99%,40.38%-55.10%,55.24%-70.66%.In addition,carbonate state and Fe-Mn oxides bound Pb content also decreased,namely the effective state Pb in the soil decreased.These four treatments improved the soil pH,incereased by 0.16-0.43,0.31-0.62,0.67-1.14,0.72-1.17 units,cation exchange capacity and organic matter also increased.The correlation analysis of Pb speciation and soil physic-chemical properties showed that pH,organic matter,cation exchange capacity,available phosphorus and available potassium were negatively correlated with effective state Pb,positively related to residual form and organic matter bound.The conductivity was just the opposite,significantly positively correlated with exchange state.6.Effects of YM-1and immobilized YM-1 on growth and Pb uptake of rapeThe results of pot experiment showed that growth promoting effects in YM-1 treatment,mushroom residue treatment,YM-1+mushroom residue treatment,immobilized YM-1 treatment were all significantly higher than control.Under different Pb concentration(0-400 mg·kg^-1),the biomass of rape in four treatment groups respectively increased by 7.7%-15.33%,5.81%-16.56%,14.53%-24.63%,18.02%-31.34%compared with control.The changes of stem and root length in each group were similar to that in biomass,both higher than control group（P<0.05）.Pb contents in rape were also significantly decreased,the largest decrease in underground were 50.00%,43.26%,75.01%,93.26%,and above-ground were 30.95%,50.00%,90.48%,99.52%.The antioxidant enzymes,chlorophyll and proline in rape also reflected the four treatments effectively promoted the growth of rape and alleviated the toxicity of Pb for rape.