Study On Isolation And Double-stage Pretreatment Of A Lignin Degrading Fungus

Lignocellulosic biomass is considered one of the most promising feedstocks for the production of cellulose derivatives due to its abundant sources and renewable sources.Due to the complex structure of lignocellulosic biomass and the crystallization region formed by hydrogen bonds in and between chains,natural lignocellulosic biomass is highly resistant to enzymatic hydrolysis.Biological pretreatment has become a research hotspot due to its characteristics of environmental protection,pollution-free and low energy consumption.In this study,a lignocellulose-degrading fungus was isolated from a local natural forest in Sichuan,and the double-stage pretreatment process was used to enhance the efficiency of reducing sugar production from corn straw.The main results are as follows:(1)A strain with the ability to degrade lignocellulose and degrading lignin was selected and identified as Trametes hirsuta by colony morphology and ITS region sequencing.The effects of initial p H,carbon source,nitrogen source,and carbon-nitrogen ratio on the enzyme production of the strain were investigated.The results showed that the best initial p H was 4.5,the best carbon source was glucose,the best nitrogen source was peptone,and the best C/N ratio was 20/2.5.Under the optimal conditions of liquid enzyme production,Laccase,Lignin Peroxidase(LiP)and Manganese Peroxidase(MnP)enzyme activities of Trametes hirsuta were 330.28 IU,272.31 IU,and 695.23 IU,respectively.(2)The optimal technology or reducing sugar production from corn straw treated with Trametes hirsuta was studied.The results showed that the optimal process conditions were as follows: the substrate particle size,>40 meshes;the inoculation amount,42 mg(dry weight)/6 g corn stalk.And the substrate lignin removal rate and reducing sugar yield were 43.60% and 251.25 mg/g substrate after 30 d of incubation time at the optimal process conditions.The double-stage pretreatment is a way in which the substrate is resterilized and reinoculated after a period of biological pretreatment.When the total treatment time is(15 d + 15 d),this double-stage pretreatment showed the highest lignin removal efficiency(62.9%),1.5-fold higher than single-stage pretreatment,and reducing-sugar yield(315.20 mg/g substrate)56.43 mg/g substrate higher than single-stage pretreatment.The enzyme production test showed that the enzyme activities(Lac,Li P,Mn P,Xylanase and CMCase enzymes)showed similar activities in the pre-and post-stage pretreatment systems and single-stage pretreatment systems.(3)Comparative study on the treatment effect of double-stage pretreatment on corn straw.treated with several strains.The results show that the lignin removal rate of substrate after double-stage pretreatment by Irpex lactues,Perenniporia tephropora and Trametes lactinea is significantly higher than that after single-stage pretreatment,and the yield of reducing sugar increase significantly compared with single-stage pretreatment.The Lac,Li P and Mn P enzyme activity peaks in the pre and post stages of double-stage pretreatment were close to that of single-stage pretreatment.