Lignin conversion to β-ketoadipic acid by <i>Pseudomonas putida</i> via metabolic engineering and bioprocess development

TLDR

Bioconversion of a heterogeneous mixture of lignin‑related aromatic compounds to a single product via microbial biocatalysts is a promising approach to valorize lignin. The study engineered *Pseudomonas putida* KT2440 to convert mixed p‑coumaroyl‑ and coniferyl‑type lignin‑related aromatic compounds into β‑ketoadipic acid, a precursor for high‑performance polymers. The engineered strain expressed tuned enzymes for aromatic O‑demethylation, hydroxylation, and ring‑opening, and a global regulator was deleted to enhance conversion. The engineered strain produced β‑ketoadipate at titers of 44.5 g L⁻¹ from model LRCs and 25 g L⁻¹ from corn stover‑derived LRCs, with productivities of 1.15 and 0.66 g L⁻¹ h⁻¹, an overall yield of 0.10 g g⁻¹ lignin, and a minimum selling price of $2.01 kg⁻¹, competitive with fossil adipic acid.

Abstract

Bioconversion of a heterogeneous mixture of lignin-related aromatic compounds (LRCs) to a single product via microbial biocatalysts is a promising approach to valorize lignin. Here, Pseudomonas putida KT2440 was engineered to convert mixed p-coumaroyl- and coniferyl-type LRCs to β-ketoadipic acid, a precursor for performance-advantaged polymers. Expression of enzymes mediating aromatic O-demethylation, hydroxylation, and ring-opening steps was tuned, and a global regulator was deleted. β-ketoadipate titers of 44.5 and 25 grams per liter and productivities of 1.15 and 0.66 grams per liter per hour were achieved from model LRCs and corn stover-derived LRCs, respectively, the latter representing an overall yield of 0.10 grams per gram corn stover-derived lignin. Technoeconomic analysis of the bioprocess and downstream processing predicted a β-ketoadipate minimum selling price of $2.01 per kilogram, which is cost competitive with fossil carbon-derived adipic acid ($1.10 to 1.80 per kilogram). Overall, this work achieved bioproduction metrics with economic relevance for conversion of lignin-derived streams into a performance-advantaged bioproduct.