The Study Of Lignin Degradation By Bacillus Ligniniphilus L1

Lignin is a complex aromatic heteropolymer comprising phenylpropanoid units linked via a variety of ether and carbon-carbon linkages. Lignin is the most abundant aromatic compounds in the world, its decomposition is closely related to the carbon cycle. The conversion of lignocellulose to cellulose is a key step of second generation biofuel production, but lignin is a very stable compound and resistance the lignocellulose to breakdown. In addition, lignin is the second most abundant of biomass in the nature and it mainly derived from the byproducts of cellulosic ethanol and pulp and paper industry or from agricultural and forestry waste. If biocatalytic routes for lignin degradation could be developed, then lignin represents a potentially source of aromatic chemicals. Despite the study of fungal lignin degradation has obtained many interesting results and found many enzymes and clarified many pathways, however, there is still no commercial bio-conversion of lignin. Since a wide range of growth conditions and good environment adaptability of bacteria, many researchers focus on the bacterial lignin degradation. And more and more studies show that bacteria play an important role in the biodegradation of lignin.In this study, we isolated a bacterium Bacillus ligniniphilus L1 which can use the lignin as the sole carbon source from bacteria deposited in our lab, indicated its potential ability for lignin degradation. To further determine the ability of Bacillus ligniniphilus L1 to degrade lignin and its mechanisms and pathway for lignin degradation. The degradation of lignin by Bacillus ligniniphilus L1 was systematic studied. Some main results are summarized as follows:1. The bacterium Bacillus ligniniphilus L1 growth well when it was incubated in medium with lignin as sole carbon source. The results showed that the chromaticity decreased by 30% when cells incubated in pH 9 in lignin medium. The extracellular peroxidase enzymes were detected during incubation process. The greatest activities of laccase was 147 U/L and 273.6 U/L for manganese peroxidase were observed. Comprehensive data shows that Bacillus ligniniphilus L1 able to degrade lignin.2. Many aromatic compounds were found during the process of Bacillus ligniniphilus L1 grown in lignin medium base on GC-MS analysis, therefore, lignin was break down to low molecular aromatic compounds by Bacillus ligniniphilus L1 and then aromatic compounds were further degraded. There are a lot of industrially valuable compounds such as vanillin in metabolites of lignin degradation.3. Bacillus ligniniphilus L1 were cultured under glucose medium and lignin medium, RNA extraction, RNA sequencing and transcriptome analysis of Bacillus ligniniphilus L1 differential expression genes. Compared with glucose medium, 1689 genes in lignin medium were differentially expressed. A total of 1168 genes were upregulated and 521 genes were downregulated. The GO enrichment analysis of differentially expressed genes was carried out through GOseq. There were 254 genes classified as cellular components, 860 genes classified as biological process and 1221 genes classified as molecular function. Pathway enrichment analysis of differentially expressed genes was subsequently carried out based on KEGG database. There have the most genes involved in Metabolism pathway.4. We also found rich genes involved in lignin degradation through RNA sequencing. It contained many genes encoding laccase, protocatechuate-2,3-dioxygenase and catechol-2,3-dioxygenase. We preliminary deduced metabolic pathways of lignin degradation by Bacillus ligniniphilus L1, it maybe degrade lignin through meta-cleavage pathway of catechol and cleavage of protocatechuate.