Identification of pathways for the catabolism of lignin-derived aromatic compounds in Xanthomonas axonopodis pv citri

Abstract

Lignin is an aromatic heteropolymer that accounts for about 30% of the organic carbon available in our biosphere. In plants, it confers mechanical resistance to cells, support to the vascular system and resistance against pathogens. In industry, it is one of the main byproducts of the paper and cellulosic ethanol manufacturing process, being produced in the range of thousands of tons per year. Although it is a promising source of renewable aromatic compounds for the chemical industry, lignin's current fate has been burning for energy production. This is partly due to the lack of consolidated processes for converting it to higher value-added products. One of the main bottlenecks for lignin valorization is its structural heterogeneity. The depolymerization of lignin results in a heterogeneous mixture, which poses considerable technical challenges for reaching high purity products. In this context, microorganisms capable of converting this heterogeneity into central carbon metabolism compounds have been widely studied in order to develop a biotechnological solution to this issue. Few bacterial species, such as Pseudomonas putida, have been studied and genetically modified for this purpose. However, other apparently promising species, such as those from the genus Xanthomonas, remain largely unexplored. Thus, the scope of this project is to identify conversion routes of lignin-derived aromatic compounds, using Xanthomonas axonopodis pv citri as a model. With this, we hope to reveal genes that may be useful for the development of microbial platforms for lignin valorization. (AU)