# Biochemical parallels between catabolic pathways for lignin-associated aromatic dimers

## TL;DR

This paper explores how fungi and bacteria break down lignin into useful compounds, focusing on biochemical pathways for aromatic dimers to improve industrial applications.

## Contribution

The paper identifies new and parallel biochemical pathways for assimilating lignin-associated aromatic dimers.

## Key findings

- Foundational pathways for monomeric aromatic compounds and select dimers are well-characterized.
- Recent advances reveal additional pathways for dimer assimilation, including new substrates and parallel routes.
- Comparing these pathways can guide metabolic engineering for lignin valorization.

## Abstract

Lignin is one of the most common biopolymers on Earth. In nature, lignin is primarily deconstructed by fungi into mixtures of aromatic compounds that are then assimilated by bacteria and fungi. Industrially, lignin is primarily generated as a byproduct of pulp and paper production and burned for process heat. However, if the appropriate assimilatory pathways were identified, deconstructed lignin could be funneled into value-added products using engineered bacteria. Foundational work has described pathways for assimilation of diverse monomeric aromatic compounds such as protocatechuate, ferulate, and syringate, as well as select dimers including those with β-O-4 and 5-5 interunit linkages. Recent advances have elucidated additional pathways for dimer assimilation, including pathways for new substrates as well as parallel pathways for previously characterized substrates. Comparing these dimer assimilation pathways can illuminate the underlying biochemical logic of assimilation for lignin-associated aromatic dimers and provide opportunities for metabolic engineering to enhance lignin valorization.