State-of-the-art lignin depolymerization and its routes to microbial valorization

Area of Science:

• Biomass Valorization
• Renewable Aromatic Chemistry
• Biotechnology

Background:

• Lignin, a major component of lignocellulosic biomass, is an abundant but underutilized renewable aromatic resource.
• Efficiently converting lignin requires understanding depolymerization and its integration with downstream bioconversion processes.

Purpose of the Study:

• To systematically review state-of-the-art lignin depolymerization strategies.
• To highlight microbial upgrading of lignin-derived aromatics into value-added products.
• To emphasize integrated depolymerization-to-valorization designs for sustainable biorefineries.

Main Methods:

• Evaluation of physical, chemical (catalytic, oxidative, reductive, solvolytic), and biological depolymerization methods.
• Review of microbial upgrading techniques including pathway engineering, synthetic biology, and systems metabolic engineering.
• Focus on developing microbial cell factories for efficient carbon funneling and selective biosynthesis.

Main Results:

• Physical methods enhance accessibility but require coupling for effective bond cleavage.
• Chemical methods achieve targeted cleavage of lignin linkages, yielding phenolic monomers and oligomers.
• Biological methods offer selective modification under mild conditions, facing challenges in rate, heterogeneity, and scalability.

Conclusions:

• Integrated strategies combining chemical and biological depolymerization with robust microbial valorization are crucial.
• These approaches provide a foundation for cost-effective, scalable, and sustainable lignin biorefineries.
• This facilitates the development of a circular bioeconomy by unlocking lignin's potential.