Screening Of Lignin Degrading Strains And The Degradation Of Lignin In Straw

Fossil fuels such as oil,coal and natural gas are non renewable resources,which are increasingly exhausted.It is particularly important to develop renewable new energy.Bioenergy meets the requirements of sustainable development and has great advantages.The storage of agricultural waste straw is huge,but most of the straw has not been used effectively.Cellulose in straw can be fermented to produce bioethanol and other energy which can be used.However,the interaction between lignin and cellulose blocks the effective utilization of cellulose,so it is necessary to remove the protective effect of lignin on cellulose.Microorganisms in nature degrade lignin by producing laccase,lignin peroxidase and manganese peroxidase.Therefore,it is very important to screen efficient lignin degrading microorganisms for rapid degradation of straw lignin.In this study,the microorganisms with lignin degradation ability were obtained by screening,and the dominant strains were identified by morphology and molecular biology.The ability of producing lignin degrading enzyme was determined,and the effects of different culture conditions on the enzyme production were investigated to determine the optimal enzyme production conditions.In order to provide an effective way for the rapid degradation of lignin in agricultural waste straw,we studied the degradation of lignin in corn straw and rice straw by dominant strains and complex bacteria.By collecting samples,the strains were isolated and purified,and screened on the medium with alkaline lignin as the sole carbon source,and then re screened on the aniline blue identification medium,guaiacol identification medium and manganese chloride identification medium,7 strains of fungi and 7 strains of bacteria with lignin degradation ability were obtained.Through morphological analysis and molecular biological identification,they were identified as Westerdykella dispersa DY5,Chaetomium giobosum DY7,Trichoderma brevicompactum DY14,Trichoderma asperellum FS2,Trichoderma hamatum FS5,Trichoderma scalesiae FS6,Trichoderma atroviride FS9,Klebsiella pneumoniae B5,Bacillus megaterium B6,Bacillus subtilis B22,Lysinibacillus fusiformis B27,Bacillus aryabhattai B29,Pseudomonas psychrophila BS1,Pseudomonas helleri BS2.After 5 days of liquid fermentation,the laccase activity of fungus W.dispersa DY5 was 73 U/L,but the enzyme activities of lignin peroxidase and manganese peroxidase were low.The effects of carbon source,nitrogen source,initial pH,Cu²⁺concentration,temperature and inoculum amount on laccase production of W.dispersa DY5 were studied.The results showed that the laccase activity reached the maximum value of 302 U/L,which was 4.14 times higher than that before optimization,indicating that the carbon source had a great influence on the laccase production capacity of the strain.The laccase activity reached the maximum of 345 U/L after 3days of culture with ammonium tartrate as the sole nitrogen source.The laccase activity reached the maximum value of 387 U/L after 3 days in the liquid medium with pH value of 5.0.The laccase activity of the strain reached the maximum of 426 U/L after 3 days in liquid medium with Cu²⁺concentration of 0.06 mmol/L.The laccase activity reached the maximum of 454 U/L at 31?for 3days.The laccase activity reached the maximum of 504 U/L after 4 days of culture with 3%(w/w)inoculum.The laccase activity of W.dispersa DY5 increased by 6.9 times after optimization.The degradation ability of the dominant strain W.dispersa DY5 and its complex flora on the lignin of corn straw and rice straw was studied.In the solid-state fermentation of corn straw,the laccase activity of W.dispersa DY5 reached the maximum of 141 U/L after 15 days of culture,and the laccase activity of fungi and bacteria complex reached the maximum of 108 U/L;After 20 days of culture,the laccase activity of fungal complex flora was 144 U/L,and that of bacterial complex flora was 35 U/L.After 60 days of solid-state fermentation of corn straw,the degradation rates of lignin by W.dispersa DY5,fungi,bacteria,fungi and bacteria were 34%,42%,46%and 54%,respectively.In the solid-state fermentation of rice straw,the laccase activity of fungi and bacteria reached the maximum of 306 U/L after 10 days of culture;After 15 days of culture,the laccase activity of W.dispersa DY5 reached the maximum of 323 U/L,and the laccase activity of fungal complex flora reached the maximum of 364 U/L;After 20 days of culture,the laccase activity of bacterial complex was 59 U/L.After 60 days of solid fermentation of rice straw,the degradation rates of W.dispersa DY5,fungi,bacteria,fungi and bacteria were 49%,62%,52%and 73%respectively.The results showed that the dominant strain W.dispersa DY5 had higher laccase activity,and the composite bacteria had better degradation ability to lignin of corn straw and rice straw,and the degradation effect of composite bacteria was better than that of single strain.