Mechanism Of Lead Biosorption And Biotransformation In Specific Microorganism In Soils Of Lanping Lead-Zinc Mine Area

Soil pollution with heavy metals is becoming one of the most severe environment and human health hazards.Phytoremediation,using plants for the restoration of pollutants in environment,is an environmentally friendly,sustainable technology with no secondary pollution.Phytoremediation assisted by heavy metal specific microorganism has been highly recommended for cleaning up metal polluted soils,since specific bacteria can alleviate metal toxicity in plant through their own metal resistance system.In this paper,the mechanisms of interaction between specific microorganisms?such as Glomus mosseae?and heavy metals?such as Pb,As,Cd?and their effects on plant uptake of heavy metal were reviewed.It was found that specific microorganism can reduce the toxicity and enhance the bioavailability by biosorption,bioaccumulation and biotransformation?oxidation / reduction or ligand complexation?of heavy metals,and their secretory products?such as organic acids,auxin?can improve plant growth under heavy metal stress and thus enhance phytoextraction efficiency.The future researches may focus on disclosing the molecular mechanism of metal hyperaccumulation of heavy metal specific microorganisms and performing its application in field work.In order to investigate the mechanism of lead biosorption and biotransformation in lead-resistant bacteria in microcosmic scale,Synchtotron radiation micro X-ray fluorescence?m-SRXRF?and X-ray absorption near edge structure?XANES?was used to determine element distribution characteristics and speciation of lead?Pb?in lead-resistant bacterial strain isolated from farmland soil samples taked from a lead-zinc mine in Lanping county,Yunnan province,China.Through the different function culture medium,we isolated,cultured and counted the number of bacteria,fungi and actinomycetes in soil samples.The results showed that the main microbes in this area is the bacteria?accounting for more than95%?,followed by fungi Actinomycetes least proportion.Using Pb directional medium to separate with Pb tolerance bacteria we got the specific bacteria tolerance concentration at 200-600 m g/g.The tolerant concentration of different bacterial is different,The tolerances of specific Pb bacterial in high concentration Pb soil samples were also higher.The isolated species was identified to be Arthrobacter sp.by 16 S rDNA.The concentration of Pb biosorpted in lead-resistant bacteria was directly determined bym-SRXRF,the results showed the highest concentration was 5925 ?g/g,the bioaccumuate factor was 14.8.Speciation of Pb in lead-resistant bacteria LPS-6-3,LB medium and soil were also presented after using Pb LIII XANES,Compared with Pb LIII XANES peak shape and peak position between standard samples,it was demonstrated that the Pb in lead-resistant bacteria was mainly formed by amorphous forms like PbS?58.0%?,(C₁₇H₃₅COO)₂Pb?22.2%?,Pb₅?PO₄?₃Cl?19.8%?rather than organic Pb speciations which was exist in LB medium.Therefore,the isolated lead-resistant bacteria could biotransform Pb to sulfuric compounds or Pb₅?PO₄?₃Cl,The results of TEM-EDXA also confirm this biotransform mechanism.The biotransformation regular could be of great interest for other investigators as reference in study of bioavailability impact factor of heavy metals.