Studies On The Mechanism And Screening Of Pleurotus Ostreatus Trains Decomposing Efficiently Lignin Of Cotton Stalk

Cotton stalk is an important biological resource and contains a large number of organic matter and minerals as by-products of agricultural production. But because it is hard to be degraded, cotton stalk is often referred to as agricultural waste to incinerate. This is not only a great waste of resources, but also causes serious environmental pollution and a range of environmental issues. It is the main reason that the biodegradation of cotton straw is difficult, because lignin with special structure can only be degraded by a few fungi.In this study, chromogenic test was used for preliminary screening from12Pleurotus ostreatus strains and lignin degradation experiment was used for further screening. Then Pleurotus ostreatus cultivation experiment was used for scientific examination of this screening system. A simple and scientific system of screening strains degrading lignin of cotton was established. Both FTIR and GC/MS were used to study on cotton stalk lignin oxidation and decomposition biochemical processes. That was hoped to provide some theoretical basis for in-depth studying lignin degradation mechanisms.Main results were as follows:(1)A set of system of screening Pleurotus ostreatus strains decomposing efficiently lignin of cotton stalk was established. It included preliminary screening and further screening. In the preliminary screening process, PDA-Bavendamm method and PDA-RB method were used to select strains having strong capabilities to secret laccase and peroxidase. This method was simple, quick and low cost. The Van Soest method was used for further screening to determine lignin degradation rate and to calculate SF. This way was high accuracy, but its operation was complex, time-consuming and expensive. Combining the two screening methods, a more simple and scientific screening system could be established.(2)8strains having strong capabilities to secret laccase and peroxidase were selected by initial screening using PDA-Bavendamm method and PDA-RB method. On this basis,4strains with high SF and efficiently decomposing lignin of cotton straw were screened out by lignin degradation experiments. They were Suping Nol, Wanping No1, Suping No3and Heiping A. Among them,"Suping No1" had the strongest lignin degradation ability of cotton straw and the degradation rate was14.82%. Finally,"Suping No1" was Selected as a strain of efficiently decomposing lignin of cotton straw, and it was applied into agricultural production. (3) FTIR analysis found that aromatic ring of G-lignin and S-lignin was destroyed in lignin polymers because of cotton stalk biodegradated by Pleurotus ostreatus, and carbonyl, methyl and methoxy structure of lignin benzene ring were partially degraded. After degradation, S-lignin was lower than G-lignin. This showed that the structure units of G-lignin and S-lignin were degradated oxidatively. Meanwhile, the special groups of many lignin monomers were also checked out.Plenty of aromatic esters, guaiacyl derivatives, lilac acid and lilac aldehyde with shorter side-chain were found in degradation products by GC/MS analysis. After the bond was broken between monomers, the oxidation reaction of monomers side-chain was occurred. Furan compounds were included in products, and indirectly certified the cracking of benzene ring. These were proofs that Pleurotus ostreatus degradated lignin completely.Combining spectroscopy analysis of lignin structure and products after lignin degradation, it could be inferred that the degradation processes of cotton straw lignin by Pleurotus ostreatus were:First, the bond between monomers (such as β-0-4) was fractured in lignin polymers, and Ca-Cp oxidation of aromatic ring side chain, side-chain oxidative decarboxylation, and methoxy substitution reaction were occurred in lignin monomers at the same time. The main reason was that lignin monomers-like formed were depolymerized from lignin high polymers. Then the aromatic ring structures of lignin monomer analogues were oxidated and became open-loop, and generated low molecular aliphatic hydrocarbons. The hydrocarbons might be involved directly in the synthesis metabolism of other substances, or be oxidated directly.