Study On The Mechanism Of Lignin Degradation By Enterobacter Ludwigii

Studying the degradation of lignin is of great importance for the development of lignocellulosic energy.Its unique and complex aromatic ring structure provides the possibility of valorization of lignin degradation products.Different from the traditional physical and chemical methods,this paper uses biological method to degrade lignin.In this paper,the mechanism of degradation of lignin monomer model compounds by Enterobacter was studied,and the performance of strains to degrade lignin was further explored.The main results are as follows:1.The growth characteristics of Enterobacter and Bacillus in lignin medium were compared.Molecular biological methods were used to identify two strains of Bacillus and Enterobacter,respectively.Under the condition that lignin was the sole carbon source,the growth of two strains on the plate was compared.Two strains of bacteria were qualitatively tested by plate fading test.A low concentration lignin solution was prepared and decolorized by intracellular and extracellular enzymes.Finally,Enterobacter was selected as a follow-up experimental strain.Enterobacter can fade the aniline blue plate,and its intracellular enzyme can make the lignin solution fade to different degrees.2.The degradation pathway of coumaric acid,ferulic acid and vanillin was explored.The growth characteristics of Enterobacter were studied in different carbon sources.In liquid medium of different monomer concentration,UV scanning,high performance liquid chromatography and GC/MS were used to detect and characterize.The results showed that Enterobacter can grow on plates where the monomer is the sole carbon source.The optimum monomer concentration in the liquid medium was 1 mM.The period of Enterobacter degrading the monomer was 0-10 h,and the blue shift of the peak shape appeared in the ultraviolet scan.The liquid phase results showed that the utilization rate of the three monomers by Enterobacter was up to 99%.P-hydroxybenzaldehyde,protocatechuic acid,4-hydroxy-3-ethoxyphenylethylene glycol and vanilla were detected in the GC-MS results.Finally,the degradation mechanism of coumarnc acid,ferulic acid and vanillin was proposed.3.The ability of Enterobacter to degrade lignin was studied.The growth characteristics of Enterobacter were studied in the plates of different carbon sources.The ability of Enterobacter to degrade lignin was evaluated by measuring the degradation and decolorization of lignin solution,the determination of enzyme activity and the detection of degradation products.The results showed that the degradation rate of lignin solution by intracellular enzymes can reach 75%and decolorization rate reaches 85%.Extracellular enzyme activity is very limited.Intracellular enzyme includes laccase and peroxidase in which the latter has high activity up to 150U/L.Only a small amount of aromatic compounds were detected in the degradation products.Enterobacter had limited ability to degrade lignin.