A target chemical for bio-based plastics is produced in the model bacterium Pseudomonas putida from lignin-derived compounds

A new publication in the journal Bioresource Technology by the group of Dr. Eduardo Díaz at the Centro de Investigaciones Biológicas Margarita Salas (CSIC) presents the development of a target chemical useful for the production of bio-based plastics. In the work, result of a collaboration with the groups of Dr. Juan Nogales (CNB-CSIC) and Dr. Tim Bugg (Warwick University, UK), and the company Biome Bioplastics (UK), a battery of genetically engineered Pseudomonas putida strains have been designed that are capable of producing the building block 2,4 pyridine dicarboxylic acid (2,4 PDCA), an analog of terephthalate (widely used for the synthesis of polyester plastics), using lignin-derived monoaromatics and also complex soda lignin samples as substrates.

Lignin, the aromatic component of plant biomass, is extracted and mostly discarded in amounts higher than 50 Mt per year worldwide in the context of pulp manufacture and biodiesel industries. However, biotechnological approaches that rely on the use of microorganisms may allow lignin streams to be revalorized for the production of compounds of undisputable commercial value.

The authors have rationally funneled the bacterial metabolism of lignin-derived aromatic compounds towards the generation of 2,4 PDCA, an analog of terephthalate (of petrochemical origin) for the synthesis of bio-based plastics. To that end, the native enzyme for protocatechuate ring-cleavage in the bacterium Pseudomonas putida KT2440 was replaced by a heterologous enzymatic activity that generates a new ring-cleavage product that becomes converted to 2,4 PDCA in the presence of ammonium. The recombinant biocatalysts were successfully used in a biotransformation process uncoupled to growth (resting cells process) to efficiently convert compounds such as protocatechuate (PCA), 4-hydroxybenzoate (HBA) or p-coumaric acid (pCA) into 2,4 PDCA.

Gómez-Álvarez et al. have shown that biotransformation yields and productivities (up to 0.9 g/L of 2,4 PDCA) can be significantly improved by accelerating substrate uptake and metabolism through the overexpression of genes encoding transporters (pcaK) or monooxygenase enzymes (pobA), and also by the successful recycling of the recombinant biocatalysts.

The designed P. putida biocatalysts were also able to produce 2,4 PDCA when using complex soda lignin mixtures as substrates, hence paving the way for future polymeric lignin valorization approaches.

Reference: “Bioconversion of lignin-derived aromatics into the building block pyridine 2,4-dicarboxylic acid by engineering recombinant Pseudomonas putida strains” Helena Gómez-Álvarez, Pablo Iturbe, Virginia Rivero-Buceta, Paul Mines, Timothy D.H. Bugg, Juan Nogales, Eduardo Díaz. Bioresource Technology. Volume 346, February 2022, 126638. https://doi.org/10.1016/j.biortech.2021.126638