Study On The Adsorption And Resistance Mechanism Of Yeast To Heavy Metal Lead

Lead(Pb²⁺)is a heavy metal with longstanding ill effects on human health.Although studies abound on the bioremediation of heavy-metal pollution by Pb²⁺,research on the mechanisms of Pb²⁺resistance and adsorption in yeast is still in its infancy.To address this problem,three yeast strains,Wickerhamomyces anomalous QF-1-1,Rhodotorula mucilaginosa QD-2-6 and Metschnikowia chrysoperlae QK-1-5,with different levels of Pb²⁺adsorption and resistance,were isolated from a heavy-metal polluted area of Inner Mongolia to serve as research subjects.First,the Pb²⁺adsorption capacity and resistance levels of the three yeast strains were determined.Then,the modern analytical techniques of Transmission Electron Microscopy(TEM),Fourier Transform Infrared Spectroscopy(FTIR)and examination of the dynamic changes of active substances in cells under Pb²⁺stress were used to reveal the adsorption and resistance mechanisms of the three yeast strains to Pb²⁺.Finally,by sequencing the genome of W.anomalus QF-1-1,we predicted the genes related to heavy-metal Pb²⁺adsorption and resistance of this yeast and measured the expression of related genes.The adsorption capacity and resistance of W.anomalus QF-1-1 to Pb²⁺were higher than those of R.mucilaginosa QD-2-6 and M.chrysoperlae QK-1-5.At a Pb²⁺concentration of 100 mg/L,the adsorption rate of Pb²⁺reached 99.28%±0.25%,almost completely adsorbed;the resistance to Pb²⁺stress was 8000 mg/L,6000 mg/L and 4000mg/L,respectively.The adsorption mechanism of W.anomalus QF-1-1 and M.chrysoperlae QK-1-5 for Pb²⁺was mainly the complex precipitation of cell wall groups(-OH,-C-N-and-NH,etc.)with Pb²⁺and the interaction of intracellular accumulation and ion exchange mechanisms.Under Pb²⁺stress,the soluble protein content,antioxidant enzyme(SOD,POD and CAT)activity and glutathione content of yeast were increased to improve resistance to Pb²⁺.Among them,W.anomalus QF-1-1 and R.mucilaginosa QD-2-6 had a greater ability to remove Pb²⁺-induced oxidative damage than M.chrysoperlae QK-1-5.The high adsorption and resistance capacity of W.anomalus QF-1-1 to Pb²⁺is due to is its high surface adsorption ability,which is caused by a large number of functional groups and folds on the surface,its high intracellular accumulation ability and its ability to clear oxidative damage induced by Pb²⁺,in comparison with that of M.chrysoperlae QK-1-5.R.mucilaginosa QD-2-6 has low adsorption and high resistance to Pb²⁺because it does not have ion exchange capacity,and the activity of functional groups involved in Pb²⁺adsorption and the ability of intracellular accumulation are low,but it can mount a timely defence against Pb²⁺stress.Therefore,under Pb²⁺stress,yeast should have both a high stress defense mechanism and high surface adsorption ability in order to have high adsorption and high resistance to Pb²⁺.W.anomalus QF-1-1,which has high adsorption and resistance to Pb²⁺,has a genome length of 15,501,755 bp,a GC content of 34.01%,6446 coding genes,2 5S r RNAs,435 t RNAs and 93 interspersed repeat sequences.A total of 63 ABC transporters and antioxidant genes that may be closely related to the processes of heavy-metal adsorption,transport and compartmentalization are predicted through annotations in the GO,KEGG and COG databases.Pb²⁺stress can significantly increase the expression of SODC,CTT,HSP12,VAN1,TSL1 and other genes related to adsorption and resistance,and the changes in antioxidant enzyme activity are consistent with the changes in antioxidant enzyme gene expression.