Bioconversion of a lignin-derived biphenyl dimer into the strategic building block 5-carboxyvanillic acid in Pseudomonas putida KT2440†

The design of new biocatalysts for funneling lignin depolymerization-derived dimers into added-value compounds is nowadays a major challenge in biological lignin valorization. Biphenyl 5,5′-dehydrodivanillate (DDVA) is a model-lignin dimer that contains the C₅–C_5′ linkage commonly found in lignin depolymerization mixtures. In this work, the metabolic potential of the industrially relevant Pseudomonas putida KT2440 bacterial strain was broadened by expressing synthetic DNA modules encoding selected metabolic and transport steps from the well-characterized DDVA degradation pathway of the Sphingobium lignivorans SYK-6 strain. By employing this heterologous expression strategy, we successfully developed an unprecedented resting cell-based bioprocess to convert DDVA into 5-carboxyvanillic acid (5CVA), a promising building block for the production of innovative bio-based polymers. This proof-of-concept study underscores the essential role of the associated DDVA transport systems. Furthermore, the findings reveal that P. putida KT2440 serves as an effective bacterial chassis for biotechnological processes that require the uptake of substrates through specific TonB-dependent transporters.