Study On Screening And Application Of Lignocellulose Degrading Bacteria

Lignocellulose is the most abundant renewable resource in the world.It can be transformed into new materials,biofuels or other high-efficiency products,which has huge application prospects.However,the lignocellulosic structure is complex and difficult to be degraded and utilized.A large amount of lignocellulose was burned,which not only caused a waste of resources,but also caused environmental pollution;the accumulation of difficult to degrade lignocellulose wastes not only invaded the land,but also caused the proliferation of microorganisms,diseases and insect pests.Therefore,it is particularly important to find a suitable lignocellulose treatment method.Cellulose complex enzymes can hydrolyze lignocellulose into reducing sugars,which can be further converted into biofuels.The reaction conditions are mild and environmentally friendly,so it has become a current research hotspot.The main source of cellulase is microorganisms in nature.Therefore,it is of practical significance to screen out strains that efficiently degrade lignocellulose.In this study,a strain with higher cellulase activity was selected by collecting soil samples,enriching,primary screening,and secondary screening.After morphological and molecular biological identification,it was identified as Aspergillus niger and finally named Aspergillus niger.Q7.The enzyme production conditions of the strain were optimized,and the optimal enzyme production conditions of the strain were finally determined:the carbon source was 3%straw powder,the nitrogen source was1.5%peptone,the initial p H value was 5.0,and the fermentation temperature was30°C.At this time,the FPA enzyme activity of the strain reached 23.02 U/ml,and the bacterial growth curve and enzyme activity change curve were drawn.Then the cellulose residue before and after degradation was analyzed and determined.SEM results show that the surface structure of the degraded straw is obviously destroyed and the structure is loose;FTIR results show that after degradation,the band representing the hydrogen bonds between lignocellulose molecules is weakened,and the destruction of hydrogen bonds affects the structure of lignocellulose,hemicellulose The characteristic peaks of lignin are also weakened to varying degrees;XRD results show that some amorphous components are analyzed;TGA and DTG results show that the decomposition temperature and maximum degradation temperature(T_max)of the degraded straw have been increased.It shows that the strain A.niger Q7 has a good degrading effect on straw.The enzyme produced by the strain A.niger Q7 was preliminarily purified,and the optimum hydrolysis conditions of A.niger Q7 cellulase were determined:the optimum p H for A.niger Q7 cellulase hydrolysis was 6.0,and the optimum hydrolysis temperature was 50?.,FPA enzyme activity is 24.05 U/ml.The straw was pretreated with 1%sodium hydroxide solution,and the straw before and after the pretreatment was observed and analyzed.SEM results showed that the pretreatment effectively opened the structure of the straw,and the contact area increased;FTIR results showed that the characteristic peaks of lignin and the hydrogen bonds between the cellulose molecules of the straw after the pretreatment were broken;Increased from 18.51%to43.36%.The NREL method was used to analyze its components,and the results showed that the cellulose content of straw increased after pretreatment,and the content of hemicellulose and lignin decreased.Using A.niger Q7 cellulase to hydrolyze straw under optimal hydrolysis conditions,the results show that the content of reducing sugars produced by the pretreated straw during the enzymatic hydrolysis process increased by 47.5%compared with that before the treatment,indicating that the pretreatment is beneficial Subsequent cellulase hydrolysis.