Mechanism Of Accumulation And Tolerance To Pb By Pleurotus Ostreatus

With the rapid development of industry and mining,the problem of soil heavy metal pollution is becoming increasingly serious in China.Among which Pb is one of the heavy metals that have a higher rate of exceeding the standard.Pb in the soil is easier to enter the human body through the food chain and endanger human health.Therefore,the management of Pb-contaminated soil is urgently needed,while the bioremediation technology is becoming a focused areas in recent years.A large number of studies have found that macrofungi have a strong ability to enrich heavy metals and are expected to be used for the remediation of heavy metal-contaminated soils.However,the mechanism of fungal accumulation and tolerance to heavy metals still needs further study.In this study,a strain of Pleurotus ostreatus previously screened and acclimated was used as the test strain to study the tolerance mechanism of Pb accumulation in Pleurotus ostreatus.The main results are as follows:(1)The characteristics of growth and the accumulation of Pb on Pleurotus ostreatus were assayed in this study,as well as the distribution of Pb in cell levels.The results showed that under Pb stress(500 mg/L),the growth of Pleurotus ostreatus was inhibited to a certain extent;Pleurotus ostreatus could accumulate Pb biosorption and intracellular.The amount can respectively reach 7.52 mg/g(dry weight)and 0.95 mg/g(dry weight);the accumulation characteristics of Pb at the subcellular level were studied by means of cell fractionation,and it was found that Pb was mainly accumulated after being absorbed on the cell wall(91.15%),followed by the cell fluid(6.12%)and the organelles(2.73%).It indicated that the Pleurotus ostreatus could accumulate Pb by different modes of action.(2)The extracellular mechanisms of accumulation and tolerance to Pb in Pleurotus ostreatus were analyzed.The results showed that fungi secreted a large amount of organic acids outside under the stress of Pb,of which oxalic acid was the main component,and precipitated lead oxalate with Pb in the extracellular fluid;Through the technology of SEM and EDS,it has found that the shape of the body is blurred,the entanglement between the mycelium is tighter,the space between the mycelium is reduced,and a large amount of Pb element is accumulated on the surface of the fungi,and the results based on FTIR are found.The hydroxyl,carboxyl,and sulfhydryl groups on the cell wall may be the binding sites of Pb and play an important role in the adsorption of Pb.In addition,the X-ray diffraction(XRD)technology found that the Pb located in the cell surface may also be Pb S and Pb CO3.Therefore,it is considered that the secretion of oxalic acid and the binding of cell wall may be an important extracellular mechanism for accumulation of Pleurotus ostreatus and resistance to Pb.(3)The differences in intracellular chelating agents such as thiol compounds and oxalic acid in Pleurotus ostreatus under Pb stress were analyzed.The results showed that the sulfhydryl compounds increased significantly from 0.08 umol/g(dry weight)to 0.14 umol/g(dry weight),and the content of protein sulfhydryl compounds was mostly at 0.127 umol/g dry weight;The oxalic acid content also increased from 5 mg/g(dry weight)to 55 mg/g(dry weight).Therefore,it is believed that the biosynthesis of chelating agents such as sulfhydryl compounds and oxalic acid may be an important intracellular mechanism for the Pleurotus ostreatus to absorb and tolerate lead.(4)The whole protein analysis of Pleurotus ostreatus under Pb stress was performed by using relative and absolute quantitative isotopic labeling(iTRAQ).The results showed that under the Pb stress,the fungi protein content increased,the total number of differential proteins reached 364,174 were up-regulated,and 190 were down-regulated;these differential proteins were located in different locations of cells and were involved in cell metabolism and cells respectively by GO functional annotation analysis.Component synthesis and other biological processes,and play a role in transport,catalysis,binding;KEGG pathway annotation analysis found that differential proteins are mainly involved in energy metabolism,amino acid metabolism,MAPK signaling pathway,detoxification,oxalic acid metabolism and GSH metabolism and S metabolism and other processes.And some of the metabolic pathways such as GSH metabolism,S metabolism and oxalate metabolism pathway proteins have significant differences,indicating that a variety of proteins participate in the process of accumulates and tolerates Pb,and oxalic acid and sulfhydryl compounds play an important role.These results help us to understand the mechanism of Pb absorption and tolerance of macrofungi,which will lay a theoretical foundation for promoting the development of macrofungi remediation of heavy metal pollution.