Efficient Dual-Pathway Valorization of Lignin-Derived Vanillic Acid via Biosensor-Assisted Directed Evolution
Engineering Lignin-Derived Vanillic Acid Dual Bypass Pathways for Chorismate Platform Construction
Lignocellulose is abundant renewable biomass awaiting full exploitation, yet it is mostly limited to low-value applications. This is mainly hindered by lignin’s heterogeneous structure and inherent recalcitrance. Previous attempts to valorize lignin have developed catalytic depolymerization and biological funneling strategies, which still face challenges such as substrate toxicity and metabolic flux imbalance.
Core Strategy
“Monomer Funnel + Directional Metabolic Branch + Pyruvate Self-Supply + Hardware-Assited Microfluidic Screening”
Converge diverse lignin depolymerization products into vanillic acid (VA) as the unified intermediate, establish modular pathways for VA-to-pyruvate supply and VA-to-CHA bioconversion, and deploy droplet microfluidics to enable high-throughput mutant screening.
01 MONOMER FUNNEL MODULE
Through co-expressed oxidation enzymes and cofactor regeneration systems, multi-enzyme cascades convert lignin-derived monomers generated by electrochemical depolymerization into one product, vanillic acid (VA) — achieving the homogenization of mixed substrates. Protein expression and catalytic performance are validated to support subsequent pathway optimization.
02 VA-TO-CHA CONVERSION MODULE
The homogenized single product vanillic acid (VA) is converted into chorismic acid (CHA) in two steps via intermediate 4-hydroxybenzoic acid (4-HB). ODM demethoxylase catalyzes the transformation from vanillic acid (VA) to 4-hydroxybenzoic acid (4-HB). Biosensor-assisted directed evolution optimizes this rate-limiting enzyme.
03 PYRUVATE SELF-SUPPLY MODULE
Vanillic acid (VA) is converted into pyruvate via a complete enzymatic cascade. This cascade provides sufficient pyruvate to support the 4-hydroxybenzoic acid (4-HB)-to-chorismic acid (CHA) reaction step. To further optimize pathway performance, ribosome binding site (RBS) mutants are screened by a pyruvate synthesis-deficient biosensor.
04 Microfluidic Screening Module
Individual mutant cells are confined within water-in-oil droplets to construct independent microreactors for parallel bioconversion. The intracellular PobR biosensor converts 4-hydroxybenzoic acid (4-HB) into mCherry fluorescence signals, which is then captured in real time and processed for dielectrophoretic sorting, ultimately enabling rapid identification of high-performance odm mutants.
Technical optimization — further improve the catalytic performance of ODM demethoxylase via error-prone PCR and biosensor-assisted directed evolution, and build a low-cost modular microfluidic platform for high-throughput screening, achieving efficient in-vivo reconstruction of the non-natural VA→4-HB→CHA route.
Application expansion — extend this lignin bioconversion platform to synthesize more chorismic acid (CHA) derivatives, covering pharmaceuticals, functional materials and food additives.
Industrial potential — promote lignin biorefinery toward a green “biomass → lignin → high-value chemicals” chain, supporting carbon-neutrality goals.
Methodological value — a universal “funnel-type” modular bioconversion strategy that redirects lignin aromatic carbon away from native degradation toward value-added biosynthesis, offering reference for valorization of other renewable aromatic resources.