A Study On The Mechanism Of Degradation And Utilization Of Lignocellulose By Pleurotus Ostreatus

Pleurotus ostrestus,as one of the widely cultivated edible mushrooms in China,is qualified to degrade and utilize forestry and agricultural residues which are rich in lignocellulose for its fruiting body development.Under appropriate environment,the mycelia absorb nutrients from substrates for fruiting body reproduction of the mushroom,which significantly hinges on the yield and quality of edible mushrooms.The capacity for degrading lignocellulose,the substrate-preference,the gene and enzymes related to decomposing and gene families evolution in P.ostrestus are not well known,though many studieshave been carried out on the model fungus,e.g.Phanerochaete chrysosporium.Cultivation and breeding of edible mushrooms are difficult to achieve innovation and creation,which leads low yield,poor quality and short industrial chain.It is therefore,the study on the degradation and utilization of lignocellulose by P.ostreatus would provide theoretical support for edible mushroom industry improvement.Four studies in Pleurotus ostreatus are conducted:(1)physiological and biochemical characteristics,with qualitative medium and enzyme-determination;(2)the substrate-preference and the detailed degradation process under different treatments by using of FT-IR and Xrd;(3)the relative genes,enzymes,and pathways during lignocellulose utilization by using of transcriptome analysis;(4)the evolution of gene families related to biomass decomposition by using comparative genome analysis of RAx ML 7.2.8,R8s,CAFE and BadiRate.The study on physiological and biochemical characteristics of Pleurotus ostreatus CCEF89 shows the production of MnP and GLOX is excellent while that of cellulase is mediocre.It has a preference on ligneous plants when taking advantage of lignocellulose.The activities of CMCNa,xylanase and laccase of P.ostreatus when decomposing poplar wood sawdust are higher than those when degrading corn stalks respectively by 17.1%,20%and 400%.When decomposing substrates,it firstly attacks acid insoluble lignin,then acid soluble lignin,finally the crystalline cellulose.This process distinguishes from that in brown rot fungi.Copper ions and guaiacol,time for hyphae and fruiting period and the proportion of substrate material have influences on the fruiting body development and biological conversion.Seven enzymes are induced by lignin:MnP3,MnP6,POXA3a,Laccase-2,CYP67,CYP52 and an aromatic compounds dioxygenase.Lignin,dextran and xylan medium cause different gene expression.Nine unigenes,correlated with Mn2+ transport,binding and acyl-CoA,are down regulated when samples are treated with CuCl2 solution.Meanwhile,the activities of MnP and GLOX are decreased,which may demonstrate these unigenes are key for MnP and GLOX' function to come true.Besides,lignin induces five unigenes,Cluster-3993.31508,Cluster-3993.26196,Cluster-3993.5545,Cluster-3993.5546 and Cluster-3993.16055,to code MnP3,MnP 6 and short MnP;two unigenes,Cluster-3993.5216 and Cluster-3993.9428,to code laccase POXA3a and Laccase-2;one unigene,Cluster-3993.22471,to participate in aromatic compounds decomposing;two unigenes,Cluster-3993.29594 and Cluster-3993,to regulate cytomembrane P450 for polycyclic aromatic hydrocar-bons transformation.Above all,the lignocellulose degradation process is mainly involved in secondary metabolic pathways,which needs MnP,GLOX and laccases to participate in,and xenobiotic and catalytic metabolism,which requires kinds of coenzymes and cytochrome P450.Eight gene families are closely correlated with lignocellulose degradation:CBM1,GH6 and GH7 are important cellulose decomposition families;AA1,AA2 and AA5 are essential lignin decomposition families;CYP53 and CYP64 are indispensable gene families for xenobiotic metabolism.With gene expansion and contraction,P.ostreatus seems to be emerged at 94 million years ago and shows strong white-rot capacity.Therefore,as one of white-rot fungi,P.ostreatus has a comprehensive category and large number of ligninolyticly decomposing gene families.The evolution of these gene families directly acts on the divergence of eco-types.