Screening Of Highly Efficient Lignin-degrading Fungus In Rotten Woods And Study On Its Degradation Performance

With China's industrialization,energy demand is increasingly intensified.The production of lignocellulosic ethanol has attracted much attention,but its production cost is still high.The pretreatment of raw materials is a key step in the process of transformation.At present,a successful pretreatment has not been developed.The development of low-cost and high-efficiency pretreatment technology is the key to the research.In this study,Simple-Lattice design method was used to screen out representative decaying wood samples in order to isolate strains with high efficiency of lignin degradation.The biological pretreatment effect of biomass wastes using the isolated strains was further investigated.The results are showed as follows.(1)6 representative decayed wood samples were collected in nature.The trend of composition change was analyzed in Simplex-Lattice,and the samples with significant decreasing trend of lignin were selected as the target samples for the isolation of lignin-degrading fungi.3 strains producing high laccase and peroxidase enzymes were selected by using the PDA-guaiacol and the PDA-aniline blue selection medium,and were respectively designated as F1,F2,and F3.The colony morphology and the sequence of the their ITS region of the fungus showed that F1 was Irpex lactues,F2 was Perenniporia tephropora,F3 was Trametes lactinea.(2)The experimental results showed that F1 produced laccase(Lac),lignin peroxidase(LiP)and manganese peroxidase(MnP),simultaneously.F2 produced Lac,and LiP.F3 produced Lac and MnP.The effects of initial pH,carbon source,nitrogen source and ratio of carbon to nitrogen on enzyme production were studied.The results showed that the optimal carbon source of the three strains was 20 g/L of glucose,and the optimum ratio of carbon to nitrogen(C/N)was 20/1.5.The optimal initial pH was 4.5,4.0,4.0 for F1,F2 and F3,respectively.The optimal nitrogen source of F1,F2 and F3 was separately peptone,beef cream and ammonium chloride.Under the optimum conditions,the activity of Lac,LiP,MnP produced by F1 was 105.92 U/mL,393.71 U/mL,827.71U/mL,respectively.The activity of Lac,LiP produced by F2 was 326.42 U/mL and964.52 U/mL,respectively.The activity of Lac and MnP produced by F3 was 424.67U/mL and 356.46 U/mL,respectively.(3)Effects of particle size,microbial inoculation amount and pretreatment time on reducing sugar production of corn straw were studied.The results showed that the optimum particle size was 40-16 mesh and the optimal inoculum amount was 6 mL.The optimal pretreatment time was 20 d for F1 and 30 d for F2 and F3.Under the optimum conditions of F3,lignin degradation rate was 71.91%,the yield of reducing sugar reached662.94 mg/g substrate,and the hydrolysis rate was up to 73.46%.(4)The changes of three components(cellulose,hemicellulose and lignin)of corn straw before and after pretreatment were analyzed.There is a significant difference between the change trend of the three components of corn straw pretreated by F1 and the degradation trend of the parasitic decayed wood sample.It is speculated that the change of the composition of the original rotten wood sample was the result of the coordinated action of multiple microorganisms.For F2 and F3,the change trend of the three components after pretreatment was consistent with the degradation trend of the parasitic decaying wood samples.(5)The physical and chemical characterizations of corn straw before and after pretreatment with F1,F2 and F3 were analyzed.SEM results showed that the waxy matter on the surface of samples disintegrated and there were hyphal infestation pores after treatment.FTIR results showed that the characteristic absorption peak of lignin decreased significantly after pretreatment with F2 and F3.The results of GC-MS showed that the pretreatment of corn straw mainly consisted of wax decomposition,lignin depolymerization,side chain recombination,benzene ring decomposition and silicate exposure.Furfural and other by-products which could inhibit the enzymatic hydrolysis and fermentation process were not detected in the eluent.It is worth mentioning that the strain Trametes lactinea can efficiently degrade lignin.This can provide important reference value for pretreatment of lignocellulosic ethanol transformation by biological methods.