Characterization And Metabolic Mechanism Of Lignin Biodegradation By Comamonas Serinivorans C35

Lignin is the most abundant renewable aromatic compound of biosphere,and its biosynthesis and decomposition are closely related to the carbon cycle in nature.Lignin is amorphous three-dimensional polymers,which is composed of three phenylpropane monomers(coniferyl alcohol,sinapyl alcohol and ?-coumary alcohol)through C=C bonds and C-O ether bonds.The structure of lignin is complex and irregular with large molecular weight.Cellulose and hemicellulose are tightly wappped by lignin so that lignocellulose is difficult to be hydrolyzed or fermented,which is one of the main bottlenecks in the conversion of lignocellulose into biofuels.Cellulose and hemicellulose in biomass have been widely used in bio-ethanol,chemicals and other production currently.However,lignin as a natural renewable resource,whose quantity was the second abundant after cellulose,has not been effectively utilized because of its complex structure and difficult for degradation,which is only discarded or burnt for energy.Therefore the utilization of lignin for high value to generate aromatic compounds is of great importance for the use of biomass.The depolymerization and utilization of lignin have been researched for decades,but there were still many difficulties that can not be overcome,such as physical methods had the high consumption challenges and chemical methods caused the secondary pollution.The biological method was environmentally friendly but low efficiency.Fungi were the pioneer for lignin biodegradation in nature,but there was still no industrialization because of the great challenge in gene manipulation and protein expression.However,due to the wide range of sources,rapid growth and easy largescale application,bacteria has obtained much attention in recent years.It is of great significance to research the metabolic pathways and mechanisms of lignin degradation by bacteria,and it will provide the theoretical basis to achieve industrialization of lignin biodegradation in the future.In this paper,we explored the lignin degradation ability and metabolic mechanism by Comamonas serinivorans C35.The main research results were as follows:(1)The strain Comamonas serinivorans C35 could grown on the medium with lignin as the sole carbon source and had the strong ability to degrade lignin.The removal rate of COD in alkaline lignin and milled wood lignin medium was 44.4% and 30.8% after 7 days incubation,respectively.Strain C35 could make the aniline blue dye fade and had the ability to secrete peroxidase and laccase.(2)The detection of Fourier Transform Infrared Spectroscopy techniques(FTIR)and GC-MS technology showed that strain C35 performed positive effect on the cleavage of benzene ring,side chain,ether bonds and C=O bonds in lignin,leading to the generation of many aromatic monomers,such as 3-methyl benzaldehyde,guaiacol,vanillic acid,vanillin,syringic acid,syringaldehyde,4-hydroxybenzoic acid and ferulic acid.(3)Whole-genome sequencing and bioinformatic analyzing showed that strain C35 genome sequence contained 414 gene sequences that encoded the lignin-degrading enzymes,such as peroxidase,copper oxidase,laccase,dioxygenase and decarboxylase.Based on GC-MS and genome data,it was found that strain C35 had at least four lignin degradation pathways,including the benzoate pathway,the phenol pathway,the ?-hydroxyacetophenone degradation and the ?-ketoadipate pathway,and the ?-hydroxyacetophenone pathway was first discovered.