Microbial Production of Terephthalic Acid (TPA)

Introduction

Terephthalic acid (TPA) is a vital aromatic dicarboxylic acid, used primarily in the manufacture of polyethylene terephthalate (PET)—the world’s most widely used plastic in bottles, textiles, films, and packaging. Conventionally, TPA is synthesized through the oxidation of petro-derived p-xylene, a process linked with greenhouse gas emissions and heavy metal catalysts.

Microbial production of TPA offers a sustainable and bio-based alternative, aiming to derive TPA or its precursors from renewable feedstocks like glucose, lignin derivatives, or plant aromatics. This approach uses engineered microbial pathways to convert sugars or lignin-derived compounds into aromatic intermediates (like p-toluic acid, p-coumaric acid, or muconic acid), which are then converted to TPA via biological or chemo-enzymatic steps.

What Products Are Produced?

Terephthalic acid (TPA) – Used in:

• PET plastics (bottles, films, textile fibers)
• Polyester resins and coatings
• Engineering polymers and copolyesters
• Biobased variants: Bio-PET, PEF precursors

Pathways and Production Methods

1. From Muconic Acid

• Glucose → Shikimate → Catechol → Muconic acid → TPA
• Enzymatic steps: dioxygenase → lactonase → decarboxylase
• Final step: Hydrogenation + oxidation of muconic acid to TPA

2. p-Xylene Biosynthesis

• Engineered microbes convert glucose → isobutanol → p-xylene → TPA
• Hybrid process with biological xylene synthesis followed by chemical oxidation

3. From p-Coumaric Acid or p-Toluic Acid

• Derived from lignin degradation or ferulic acid pathways
• Microbes engineered to elongate and oxidize the side chain to generate TPA
• Co-culture and modular chassis used for complex conversions

4. Lignin Valorization Routes

• Lignin-derived monomers like p-coumaryl alcohol or syringaldehyde processed to TPA intermediates
• Uses oxidases and decarboxylases in microbial or chemo-enzymatic systems

Catalysts and Key Tools Used

Key Enzymes:

• Protocatechuate 3,4-dioxygenase, catechol dioxygenase – aromatic ring opening
• Muconate cycloisomerase, lactonizing enzymes
• Decarboxylases for final conversion to benzene dicarboxylates
• Aromatic oxidases – for lignin-derived pathways

Metabolic Engineering Tools:

• Synthetic operons to cluster multi-step aromatic pathways
• CRISPR-based knock-ins for gene stability
• Dynamic expression systems for toxic intermediates
• Transporter engineering to enable TPA export and resistance

Host Microorganisms:

E. coli Corynebacterium glutamicum , Pseudomonas putida , S. cerevisiae

Case Study: Virent & Gevo – Hybrid Biosynthesis of Bio-TPA

Highlights

• Used isobutanol-derived p-xylene from engineered E. coli
• Converted to TPA via catalytic oxidation, enabling Bio-PET bottle production
• Coca-Cola’s “PlantBottle” initiative sourced bio-TPA from this pathway
• Demonstrated bio-content of 100% for PET precursors (bio-MEG + bio-TPA)

Timeline

• 2011 – First bio-xylene fermentation at pilot scale
• 2013 – Bio-TPA integrated into PET bottle prototypes
• 2017 – Technology scaled to 10,000 L fermenters
• 2023 – TPA from muconate also tested at demonstration scale

Global and Indian Startups Working in This Area

Global

• Virent (USA) – p-xylene and TPA from isobutanol
• Gevo (USA) – Engineering isobutanol-to-aromatic pathways
• Anellotech (USA) – Biomass-to-aromatic TPA precursors
• Origin Materials (USA) – Carbon-negative PET precursors from wood residues

India

• IIT Bombay & CSIR-NCL – Aromatic pathway engineering for muconate and TPA
• IIT Guwahati – Lignin valorization to aromatic acids
• Godavari Biorefineries – Exploring hemicellulose and lignin routes to aromatics
• Startups supported by BIRAC and DBT – Working on biobased PET monomers

Market and Demand

The global TPA market was valued at USD 53 billion in 2023, projected to grow to USD 72 billion by 2030, at a CAGR of ~4.5%. Biobased TPA is currently a niche (~2–3%) but rapidly growing due to eco-friendly packaging mandates.

Major End-Use Segments:

• PET bottles and packaging films
• Textile polyester fibers
• Coatings and resins
• Engineering thermoplastics

Key Growth Drivers

• Push for biobased, recyclable, and carbon-neutral PET
• Increasing bans on virgin fossil plastics in packaging
• Technological progress in fermentation of aromatic compounds
• Lignin valorization opening new low-cost aromatic feedstocks
• Major brands committing to 100% bio-PET (e.g., Coca-Cola, Danone)

Challenges to Address

• Aromatic toxicity to microbes limits production titers
• Complex multi-step pathway assembly and regulation
• Cost of bio-TPA still higher than fossil-derived TPA
• Low yields from lignin depolymerization intermediates
• In India: limited industrial capacity for aromatic fermentation

Progress Indicators

• 2010–2013 – First microbial p-xylene and muconate-to-TPA reports
• 2015 – Hybrid fermentation + chemical oxidation scaled
• 2019 – Bio-PET pilot production by global brands
• 2022 – Indian researchers demonstrate bio-aromatic acid biosynthesis
• 2024 – Lignin-derived aromatic routes begin bench-scale validation

Microbial and hybrid bio-TPA production is at TRL 6–8 globally (pilot to near-commercial scale). In India, processes are at TRL 4–5, with academic and early startup efforts progressing in aromatic pathway engineering.

Conclusion

The microbial production of terephthalic acid (TPA) is a crucial milestone in the journey toward 100% renewable PET and polyester products. Through the strategic engineering of aromatic pathways, microbes can convert sugars and lignin into bioaromatic building blocks, supporting the future of green packaging, textiles, and polymers.

With global momentum and India’s growing interest in lignocellulosic biorefineries, bio-TPA is set to become a cornerstone molecule in sustainable plastics and materials innovation.

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