Investigation of lignin-related aromatic compounds metabolism in a Xanthomonas phytopathogen

Author(s)

Damaris Batistão Martim

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2024-02-22

Examining board members

Priscila Oliveira de Giuseppe; Ljubica Tasic; Cristina Elisa Alvarez Martinez; Maxuel de Oliveira Andrade; Daniela Barretto Barbosa Trivella

• Advisor: Priscila Oliveira de Giuseppe

Abstract

The sustainable exploitation of lignin side-streams to produce high-value chemical compounds has emerged as a promising strategy to reduce the dependency of fossil industries. In this context, the concept of using microorganisms to transform the variety of compounds resulting from the lignin depolymerization into bioproducts, formed in convergence points of microbial metabolism, has been widely explored in recent decades. However, the current knowledge of metabolic pathways responsible for the bioconversion of lignin-related compounds is still constrained to a limited number of species and elusive for some of these compounds. Therefore, the search for bacteria capable of metabolizing lignin-related compounds is essential for identifying new enzymes active on aromatics, as well as for the development of new biotechnological strategies aimed at lignin valorization. The present study aimed to evaluate the compatibility of products from hydrothermal depolymerization of lignin with bioconversion strategies in different bacterial genera, in addition to identifying and validating new pathways for the metabolism of lignin-related aromatic compounds, using as a study model a plant pathogen "Xanthomonas", a genus relatively unexplored for this purpose. The results of this work have been compiled into two scientific papers, one already published and the other submitted for publication, which are presented as chapters of the thesis. In the first chapter, we conducted analysis on the effect of hydrothermal depolymerization of isolated lignin in terms of yield, composition, and compatibility of the resulting bio-oils with microbial bioconversion. Although the heavy bio-oil with high molecular mass did not support bacterial growth, the light bio-oil, rich in aromatic monomers, promoted the growth of nine bacteria, indicating its compatibility with microbial conversion strategies. Subsequently, the second chapter extensively explores the bioconversion pathways of lignin-related compounds in X. citri subsp. citri 306 (X. citri 306). X. citri 306 was capable of metabolizing different lignin-related compounds, including the three main monolignols (p-coumaryl (H), coniferyl (G), and sinapyl (S)). Using approaches such as RNA-seq, gene knockout, and biochemical assays, we identified complete pathways for the metabolism of the three monolignols, in addition to new reductases and efflux transporters likely used by the bacterium to counterbalance the toxicity of aromatic compounds. In summary, these two chapters provide fundamental knowledge that can be used for further studies aimed at developing biotechnological strategies for utilizing lignin waste as a feedstock for a more sustainable production of chemicals (AU)

• FAPESP's process: 19/08590-8 - Identification of pathways for the catabolism of lignin-derived aromatic compounds in Xanthomonas axonopodis pv citri
• Grantee: Damaris Batistão Martim
• Support Opportunities: Scholarships in Brazil - Doctorate