Microbial Utilization of Lignin-Derived Aromatics via a Synthetic Catechol Meta-Cleavage Pathway

Lignin is an abundant organic reservoir from plant biomass that is underexploited. Microbial utilization of lignin represents a sustainable approach for a biorefinery. In this study, we diversified the bioproduction from lignin-degraded aromatic compounds based on a catechol meta-cleavage metabolism. To establish an efficient downstream ligninolytic pathway, debottlenecking of the rate-limiting protocatechuate decarboxylation and evaluation of the alternative meta-cleaving pathways at the enzymatic and metabolic levels have been conducted. As a carbon flux indicator and showcase of versatility, we devised a new synthetic route towards 1,3-BDO, resulting in 0.343 g g−1 product accumulation from protocatechuate. We further extended the pathway to successfully assimilate commonly present depolymerized lignin monomers, isoeugenol, vanillin and vanillate, to central metabolites pyruvate and acetyl-CoA, as demonstrated by biocatalysis of up to 0.153 g g−1 citramalate from these aromatic monomers. The established synthetic ligninolysis via catechol meta-cleavage can serve as an efficient platform for expanded spectrum for lignin utilization.