Ideonella Sakaiensis: Plastic-Degrading Enzymes & Polyethylene Terephthalate (PET) - UPSC Notes

Ideonella sakaiensis is a special sort of bacterium found in 2016 that can digest polyethylene terephthalate (PET), a plastic commonly used but not biodegradable. It has extraordinary enzymes, PETase and MHETase, that degrade plastic to present new options on waste disposal sustainability, environmental preservation, and global integration of plastic pollution.

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Ideonella sakaiensis is essential for UPSC GS Paper 3 under Environment, Ecology, and Science & Technology. It relates to pollution control, biotechnology, and waste management, relevant to questions on sustainable solutions to plastic pollution and environmental conservation. Join the UPSC coaching today and boost your preparation.

Prime Details Of The Latest News 

• Enhanced PETase via Protein Engineering: Researchers have successfully engineered mutant forms of PETase with significantly improved thermostability, showing up to 15 °C higher melting temperatures and higher degradation activity than the wild-type enzyme.
• New Insights Into Catalytic Mechanism: A detailed reaction mechanism of PETase was recently revealed through a computational study, which identifies the deacylation reaction as the rate-limiting step that depends on flexible residues Trp185 in the vicinity of the active site and which facilitates the active catalysis.
• Ongoing Advances in Enzyme Optimization: Continuous efforts in protein engineering are pushing PETase's performance forward—focusing on enhancing substrate binding, thermal stability, and catalytic efficiency for potential industrial and environmental applications.
• PET Degradation in Saltwater: Scientists have genetically modified the fast-growing marine bacterium Vibrio natriegens to express I. sakaiensis's PET-degrading enzymes, enabling PET breakdown in saltwater at room temperature—a significant step toward addressing marine plastic pollution.

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What is Ideonella sakaiensis?

Ideonella sakaiensis is a Gram-negative, rod-shaped, aerobic bacterium from the genus Ideonella (family Comamonadaceae), first described and named in 2016. It was isolated from PET-contaminated sediment near a recycling plant in Sakai, Japan. 

About Ideonella sakaiensis

• Discovery: Identified in 2016 by researchers led by Kohei Oda and Kenji Miyamoto at Kyoto Institute of Technology and Keio University. They observed that the bacterial consortium could degrade roughly 75% of PET into CO₂.
• Habitat: Found in oxygen-rich, moist, PET-contaminated soil—such as that around recycling sites—and in sewage sludge.
• Morphology & Growth Conditions:
  • Size: approximately 1.2–1.5 µm long by 0.6–0.8 µm wide
  • Motile via a single polar flagellum; Gram-negative, non-spore-forming, non-pigmented
  • Grows optimally at 30–37 °C within a pH range of 5.5–9.0 (optimal near pH 7–7.5)
  • Catalase-positive and oxidase-positive

Also Read the Difference Between Virus And Bacteria

Characteristics of Ideonella sakaiensis

Ideonella sakaiensis is a Gram-negative, rod-shaped, aerobic, and motile bacterium discovered 2016 near a plastic recycling plant in Japan. It produces two key enzymes, PETase and MHETase, which degrade PET plastic into simpler compounds. It thrives best at 30–37°C and neutral pH.

• Biochemical tests:
  • Catalase: +
  • Oxidase: +
  • Other tests (e.g., indole, nitrate reduction) vary; see detailed tables in sources
• Metabolism & Enzymes:
  • Produces two key enzymes:
  1. PETase: breaks down PET into intermediates like MHET and BHET
  2. MHETase: further hydrolyzes MHET into terephthalic acid (TPA) and ethylene glycol (EG)
  • Internally, EG is metabolized via the TCA cycle; TPA is oxidized and processed into protocatechuate and fed into further metabolic pathways.
• Recent discovery:
  • Under anaerobic conditions, I. sakaiensis can ferment PET to produce acetate and ethanol, offering potential for bioenergy applications in microbial fuel cells.

What Is Polyethylene Terephthalate (PET)?

Polyethylene terephthalate (PET) is a strong, lightweight, and durable thermoplastic polyester widely used in bottles, packaging, and textiles. Made from ethylene glycol and terephthalic acid, it is highly resistant but non-biodegradable, making it a major contributor to environmental plastic pollution.

• A thermoplastic polyester widely used in bottles, fibers, and packaging.
• Chemically, it's a condensation polymer made from ethylene glycol and terephthalic acid, releasing water during formation.
• Highly durable and not readily biodegradable, posing significant environmental challenges, mainly as it accumulates in landfills and oceans.

Further Reading: Microbes

Conclusion

Ideonella sakaiensis is an achievement that means a lot towards reducing plastic pollution. Its talent to break down PET naturally using PETase and MHETase is just the tip of the iceberg: researchers are improving the enzymes and applying them to harsh environments—such as ocean environments. New experiences have led to an even greater possibility, bioengineering in marine bacteria and anaerobic fermentation pathways. These are developments with the potential of more scalable and sustainable plastic recycling and bioremediation.

Also Read: Virology

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