The Plastic Eaters

Introduction: A Ticking Time Bomb

Every minute, over 1 million plastic bottles are sold globally. Polyethylene terephthalate (PET)—the lightweight, shatterproof polymer in these bottles—accounts for 12% of global solid waste. Less than 30% is recycled; the rest pollutes oceans, chokes landfills, and fragments into microplastics invading our food chain ^{1 5} . But what if we could turn this crisis into opportunity? Scientists are now engineering bacteria to "eat" PET waste and transform it into high-value products—from biofuels to $7,500/kg carotenoids. This is bio-upcycling: nature's solution to humanity's plastic nightmare.

Key Concepts: From Waste to Wealth

1. The PET Problem

PET comprises two monomers: terephthalic acid (TPA) and ethylene glycol (EG). Traditional recycling has critical flaws:

• Mechanical methods degrade plastic quality, shrinking material value by 33% ¹ .
• Chemical recycling repolymerizes PET at high cost, making it economically unviable versus virgin plastic ($1/kg) ^{1 6} .

2. Nature's Recyclers: Enzymes to the Rescue

In 2016, a breakthrough emerged: Ideonella sakaiensis, a bacterium that produces two enzymes:

• PETase: Breaks down PET into mono(2-hydroxyethyl) terephthalate (MHET)
• MHETase: Converts MHET into TPA and EG ^{1 7}

These enzymes operate at ambient temperatures, slashing energy costs. But natural degradation is slow.

3. Turbocharging Nature

Scientists engineer enzymes for efficiency:

• Thermostability: Engineering disulfide bridges into leaf-branch compost cutinase (LCC) raises its stability to 94.5°C—near PET's glass transition temperature—accelerating depolymerization ¹ .
• Dual-enzyme systems: Fusing PETase and MHETase into a single chimeric enzyme boosts degradation rates 2-fold ¹ .

4. Microbial Factories: Beyond Degradation

Once broken into TPA and EG, monomers feed engineered bacteria that convert waste into value:

In-Depth Look: The PET-to-Lycopene Experiment

Objective

Convert post-consumer PET into lycopene—a high-value antioxidant—using Rhodococcus jostii RPET without purifying monomers ^{5 6} .

Methodology

Results and Analysis

Growth: RPET thrived in 0.6M TPA/EG mix—unlike model strains (e.g., E. coli) that require purified monomers ⁵ .

Lycopene Production: Engineered strains synthesized 1.3 mg/L lycopene directly from PET waste ⁶ .

The Scientist's Toolkit: Essential Reagents for PET Upcycling

Future Perspectives: The Road to Scalability

Conclusion: A Circular Economy Within Reach

Bio-upcycling transcends waste management. By transforming PET into performance-advantaged nylon, industrial pigments, or biodegradable polymers, it creates market incentives for reclamation. With engineered consortia reaching Technology Readiness Level (TRL) 4 ⁶ , the path is clear: plastic waste is the next frontier for synthetic biology—and our planet's lifeline.