| The natural termite-fungi symbiotic system can efficiently convert lignocellulosic biomass,its essence is the destruction of physical structure and modification of functional groups of lignin,which is to enhance the accessibility of cellulose to cellulase and reduce the non-productive adsorption of lignin to cellulase,thereby improving the efficiency of enzymatic saccharification and providing new ideas for the efficient utilization of lignocellulosic energy.Based on the existing literature research,the known degradation effect on lignin within the termite-fungi natural symbiotic system is Laccase（La）in the termite gut and Termitomyces sp.（Te）in the nest.Therefore,this study proposed a new system for synergistically pretreating lignin based on La and Te（La+Te）.The lignin model compound alkali lignin and the actual lignocellulosic biomass wheat straw were used as pretreatment substrates to study the effect of single La,single fungi and enzyme-fungi synergistic system on alkali lignin and wheat straw pretreatment,analysing the changes of physicochemical properties of alkali lignin and the effect of subsequent enzymatic hydrolysis after alkali lignin was pretreated by enzyme and fungi and clarifying the law of enzyme and fungi system on lignin synergistic pretreatment is to provide guidance for lignin pretreatment.On this basis,we further investigated the conversion characteristics of wheat straw pretreated by the enzyme-fungi synergistic system and elucidated the mechanism of the enzyme-fungi synergistic system to improve the conversion efficiency of wheat straw.Finally,we investigated the effect of enzyme-fungi synergistic system on the enzymatic hydgolysis and fermentation characteristics of wheat straw,and verified that the enzyme-fungi synergistic system could effectively improve the efficiency of wheat straw conversion to fuel ethanol.The main conclusions are as follows:A nature inspired enzyme-fungi synergistic system,La+Te synergistic system,was constructed to compare with single La,single fungi and La+Phanerochaete chrysosporium（La+PC）synergistic system on fungal biochemical properties and alkali lignin conversion characteristics.The lignin-degrading enzyme laccase（La）and lignin peroxidase（Li P）activities secreted by La+Te synergistic system were increased by 43.3%and 58.5%,respectively,compared with single Te,and the lignin-degrading enzymes La and manganese peroxidase（Mn P）secreted by La+PC synergistic system were increased by 35.9%and 31.6%,respectively,compared with single PC.La+PC synergistic system enhanced the alkali lignin degradation rate by 6.7%compared with single PC.Fourier transform infrared spectroscopy（FTIR）results showed that the enzyme-fungi synergistic system had a significant effect on the modification of lignin functional groups.Thermogravimetric analysis（TGA）showed that the alkali lignin pretreated by the enzyme-fungi synergistic system were more susceptible to thermal decomposition and molecular structure disruption than single fungi.Scanning Electron Microscope（SEM）results and pore size analysis showed that the enzyme-fungi synergistic system caused serious damage to the structure of alkali lignin,the number of surface holes was increased and the average pore size increased significantly.The maximum adsorption of alkali lignin pretreated by La+Te synergistic system to cellulase was 51.5%less than that of untreated alkali lignin sample.Due to the significant reduction of non-productive adsorption,the subsequent enzymatic hydrolysis conversion rate was 71.5%higher than that of untreated alkali lignin sample.La+PC synergistic system significantly increased the removal rate of lignin by 240%compared with single PC,and increased the retention rate of cellulose and hemicellulose by 13.6%,10.2%,respectively.The lignin degradation,cellulose and hemicellulose retention rates of La+Te synergistic system and single Te were basically the same.The reducing sugar yield of wheat straw pretreated by La+PC synergistic system after enzymatic hydrolysis was increased by 29.6%compared with single PC.X-ray diffraction（XRD）results showed that the enzyme-fungi synergistic system could reduce the crystallinity of wheat straw.Thermogravimetric analysis showed that the enzyme-fungi synergistic system had higher thermal stability than untreated wheat straw sample.FTIR results showed that the absorption peak intensity of each functional group in the range of400cm-1～4000 cm-1 was enhanced in wheat straw pretreated by the enzyme-fungi synergistic system.SEM results showed that the physical structure of wheat straw surface was severely damaged after the enzyme-fungi synergistic system pretreatment,and rectangular cavities with a length of about 10μm appeared,which improved the accessibility of cellulase to cellulose and facilitated the subsequent enzymatic saccharification and fermentation process.The ethanol yield rate of wheat straw before and after enzyme-fungi pretreatment was the fastest in the early stage of fermentation,after which the ethanol concentration began to decrease.The highest peaks of ethanol production of wheat straw enzymatic hydrolysis solution before and after enzyme and fungi pretreatment occurred within the first 12h.The highest ethanol yield of wheat straw enzymatic solution was obtained after single Te and La+Te synergistic system pretreatment,indicating that the pretreatment of wheat straw by Te could significantly enhance the subsequent ethanol yield.the highest ethanol yield of 1.14 g/L was obtained after La+Te synergistic system pretreatment,and the glucose fermentation utilization was 29.0%higher than that of single Te.The ethanol yield and glucose fermentation utilization of La+PC synergistic system were 74.4%and33.7%higher than those of single PC,respectively. |
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