Scaling‐up the Bioconversion of Lignin to 2,4‐Pyridinedicarboxylic Acid With Engineered <i>Pseudomonas putida</i> for Bio‐Based Plastics Production

2,4-pyridinedicarboxylic acid (PDCA) is a promising bio-based compound to substitute petroleum-derived terephthalic acid in plastics. It is produced through the microbial conversion of lignin substrates with engineered microorganisms like Pseudomonas putida. To this point, an efficient bioproduction process for PDCA has not yet been established. In this study, we optimized PDCA production with engineered P. putida ligAB and demonstrated bioproduction at up to 30 L scale. PDCA was produced with a volumetric productivity of 390 mg/L/h from the precursor protocatechuate and the product titer was doubled compared to previously reported work. Lignin feedstock and pretreatment combinations were screened to access lignin as substrate for PDCA production. Sodium hydroxide lignin with alkali + heat pretreatment yielded 33 mg/L PDCA at a production rate of 0.1 mg/g/h. Low PDCA production rates could be overcome by developing a bacterial mixed culture by adding the engineered strain Rhodococcus jostii ΔpcaHG that supplies PCA from lignin degradation. The mixed culture increased PDCA productivity of P. putida ligAB by factor 19 (1.9 mg/g_{P. putida}/h).