Study On Screening And Characteristics Of Heavy Metal-tolerant Strains And Their Application

Heavy metal pollution is increasing with metals exploitation and application.Pollution has become the focus of attention.Chemical remediation and bioremediation has been paid much attention in recent years,and has made significant progress.The interaction of amendments and microbial remediation used in contaminated soils also are rarely reported.It could effectively improve the ability of contaminated soil bioremediation.We used amendments to promote the microbial strains selected in the contaminated soil accumulating Cd and Pb,and to apply to the remediation of the soil contaminated by heavy metals.Some strains resisted to high concentration of cadmium were isolated by acclimation of concentration gradient from the polluted soils in Hunan province.The strains were marked F1 and F2 with higher resistance were selected in the following experiments.Strain F1 could survive in 3500 mg/L Pb2+ solid medium and 3200 mg/L Pb2+ liquid medium.Strain F2 could survive in 1200 mg/L Cd2+ solid medium and 40 mg/L Cd2+ liquid medium.Scanning electron microscope observation showed,vegetative mycelium wall of F1 was smooth,and the mycelia had septate and branches and the size was 1.5 ?m-3.1 ?m.Conidia presented oval and the size was(2.0-2.3)?m ×(1.6-2.7)?m.The strain F2 was identified as Trichoderma asperellum based on the morphologic characteristics and the sequences analysis of ITS rDNA.Scanning electron microscope observation showed,vegetative mycelium wall of FI was roughness and had septate and branches,and the size of diameter was 5.0 ?m-5.5 ?m.The strain F2 was identified as Cunninghamella bertholletiae based on the morphologic characteristics and the sequences analysis of ITS rDNA.The strains could resist not only to Cd and Pb,but also to other metals including Cu.The growth and resistance conditions of two strains were as follows.The suitable of conditions were all improved liquid medium,and the culture time of seed solution was 36 h and 24 h,respectively,and the cultivation time of the fermented liquid was 108 h and 132.The suitable of resistance conditions were 30? and 35?,PH 7 and 4,108 h and 84 h.Bacteria content was 6%(v/v),and the concentration of the mineral quality was 0.05 g/L.The culture concentration was 800 mg/L and 40 mg/L,respectively.Analysis by IR spectroscopy,hydroxide,acylamide,carboxyl,C-N and carbonyl were main adsorption spots.Analysis by SEM,the adsorption mechanisl of PbrDwas based on the adsorption precipitation effect of cell surface,and the dsorption of Cd2+ was based on its surface.A modified BCR three-step sequential extraction procedure was used to determine Cd and Pb speciation in the contaminated soil.Pot experimental results showed,the exchangeable,acid-and water soluble Cd and Pb were reduced,and the sulfide and the organic combination state and residual Cd and Pb were increased.They effectively reduced the active state content of heavy metal to significantly reduce the content of Cd and Pb in Chinese cabbage.