Every year, the world produces over 27 million metric tons of PET plastic. This is the material found in bottles, food packaging, and textile fibres. Less than 15% of it gets properly recycled. The rest ends up in landfill, incineration, or the natural environment, where it can persist for over 2,500 years. Solving this problem requires better recycling technology. One of the most promising directions comes from an unlikely source: microorganisms living in some of the most hostile environments on Earth. These organisms produce extremozymes — enzymes that stay active under extreme conditions. Their potential for extremozymes PET recycling is now one of the most active areas in industrial biotechnology.
This is one of the core research directions of the EXPLORA project. By prospecting the Río Tinto river in Spain and the Antarctic region for novel microorganisms, EXPLORA aims to find plastic-degrading acidophilic enzymes that work where standard biology fails. Moreover, the project validates these enzymes for real industrial use — connecting fundamental science to the circular economy.
What are extremozymes?
An enzyme is a biological molecule that speeds up a chemical reaction. Standard enzymes work well under mild conditions — roughly neutral pH, moderate temperature, and low metal concentrations. However, when conditions become harsher, most standard enzymes unfold and stop working entirely.
Extremozymes are different. They come from organisms that live in environments most life cannot tolerate. For example, they inhabit boiling hot springs, highly acidic rivers, frozen Antarctic soils, or water full of toxic metals. As a result, these enzymes evolved molecular structures that remain stable and active under exactly those conditions. In addition, some extremozymes stay active under more than one type of extreme at once. That combination makes them particularly robust for industrial use.
Extremozymes PET recycling: why the match makes sense
PET plastic holds together through ester bonds. Extremozymes called polyesterases and cutinases are built to break exactly that type of bond. Standard PET-degrading enzymes face a key problem, though. They work best at mild temperatures, but PET only becomes flexible enough for efficient enzymatic attack at 65 to 85°C. According to research published in Nature Communications, less than 10% of known PET-degrading enzymes remain active at that range. Consequently, most promising candidates fall apart before they can do useful work at industrial scale. Extremozymes, by contrast, evolved to stay active in harsh conditions. Therefore, enzymes from acid-tolerant or heat-resistant microorganisms are strong candidates for bridging this gap.
Why standard enzymes fail at industrial scale
Current PET recycling relies on mechanical and chemical processes. Mechanical recycling grinds plastic into pellets, but it degrades quality with each cycle. Chemical recycling breaks PET down into its building blocks, but it needs temperatures above 200°C. Moreover, it generates toxic byproducts. Both approaches are energy-intensive and costly at scale.
The enzyme alternative
Enzymatic recycling offers a cleaner route. Rather than using heat and harsh chemicals, it uses biological molecules to break PET into two core components: terephthalic acid and ethylene glycol. These components can then make new, virgin-quality PET. According to research in Microbiology and Molecular Biology Reviews, over 255 verified plastic-active enzymes from more than 11 microbial groups are now known. Nevertheless, the challenge remains the same. Most of these enzymes are not stable enough for industrial conditions. This is precisely the gap that extremozymes aim to fill. For a broader understanding of what makes multi-stress organisms so valuable, our article on polyextremophiles and their industrial potential explains the biology in depth.
What makes extremozymes structurally different
Extremozymes tend to have tighter, more rigid protein structures than standard enzymes. They also feature stronger internal molecular bonds and specialised outer layers. These features prevent unfolding under heat, acid, or metal stress. Consequently, they stay functional in conditions that would destroy a standard enzyme within minutes. Furthermore, these same structural features often translate across different types of stress — meaning an acid-stable enzyme may also show useful heat tolerance.
Río Tinto as a source of plastic-degrading enzymes
The Río Tinto river in Huelva, Spain, runs at a pH between 1.5 and 2.5. It also carries dissolved iron, copper, arsenic, and zinc at levels that would kill most organisms. The microorganisms that thrive here — including iron-oxidising bacteria like Acidithiobacillus ferrooxidans — produce enzymes that work under precisely those conditions. For a detailed account of the microorganisms that live in the Río Tinto river, our dedicated article covers each group in full.
Why acid-tolerant enzymes matter for PET recycling
Ester bonds in PET are chemically similar to the bonds these organisms break in sulfide minerals every day. Moreover, the structural features that allow Río Tinto enzymes to work at pH 1–2 — rigid protein cores and reinforced molecular bonds — also tend to confer heat stability. As a result, acid-tolerant polyesterases from the Río Tinto may naturally carry some of the thermostability that industrial PET recycling requires.
In addition, research published in Frontiers in Microbiology shows that combining enzyme discovery with computational modelling is currently the most promising route to industrial-scale PET degradation. EXPLORA’s pipeline — from field sampling to high-throughput screening — targets exactly this approach.
Antarctica as a second source of extremozymes
Cold environments add a different angle to extremozymes PET recycling research. Antarctic psychrophiles — cold-loving organisms — produce enzymes that work efficiently at low temperatures. Thin PET films, for example, have a softening point as low as 40–44°C. Cold-active extremozymes from Antarctic microorganisms can operate effectively in that range.
Cold-active enzymes and their advantages
Beyond PET recycling, cold-active extremozymes have uses across pharmaceuticals, food processing, and cosmetics. They drive reactions at lower temperatures, which reduces energy costs in industrial processes. Furthermore, many Antarctic organisms produce antioxidants and protective compounds as part of their cold-adaptation strategy. These compounds have direct applications in nutraceuticals and skincare products. For a full picture of the microorganisms that live in Antarctica and the habitats they occupy, our dedicated article covers cold-adapted life in full detail.
From extreme environment to circular economy
The path from a microorganism in the Río Tinto to a validated industrial enzyme is long. First, researchers must collect samples legally and safely — a process governed by the Nagoya Protocol for the Río Tinto and by the Antarctic Treaty for polar samples. Next, they use next-generation DNA sequencing to identify which organisms are present and which genes they carry. Then, computational modelling and AI-assisted screening help narrow down the most promising enzyme candidates without culturing every isolate individually.
How EXPLORA turns discovery into application
Once EXPLORA identifies a candidate enzyme, the next step is validation — testing activity against PET under conditions that reflect real industrial processes. That means testing at varying temperatures, pH levels, and substrate concentrations to build a clear picture of where the enzyme works, where it fails, and what engineering might improve it further.
This pipeline sits at the heart of what makes EXPLORA’s approach to extremozymes PET recycling scientifically distinctive. Rather than starting from known organisms and modifying their enzymes, the project starts from environments that evolution has already optimised for multi-stress stability — and works forward from there. The result, if successful, is a class of enzymes that industry can use to recycle PET more efficiently, at lower temperatures, and with fewer harmful byproducts than any current method allows.
That outcome matters not just for biotechnology. It matters for Europe’s transition to a circular economy — one where plastic waste becomes a raw material rather than a long-term environmental problem.
Frequently asked questions about extremozymes and PET recycling
What are extremozymes? Extremozymes are enzymes produced by organisms that live in extreme environments — highly acidic rivers, frozen soils, volcanic hot springs, or metal-rich water. Because these organisms evolved under harsh conditions, their enzymes remain stable and active where standard enzymes would break down. As a result, they are valuable for industrial processes that require biological activity under demanding conditions.
Why are extremozymes useful for PET recycling? PET plastic becomes soft and accessible to enzyme attack at temperatures between 65 and 85°C. However, most known PET-degrading enzymes fail at those temperatures. Extremozymes from heat- and acid-tolerant organisms carry structural features that may allow them to stay active in that range — making extremozymes PET recycling one of the most promising routes to efficient, clean, and scalable plastic recycling.
Where does EXPLORA look for plastic-degrading enzymes? EXPLORA searches the Río Tinto river and the Antarctic region. Both sites host microorganisms that produce enzymes active under multiple simultaneous extreme conditions. Those same structural features that allow activity in acid, cold, and metal-rich environments may also provide the robustness needed for industrial PET recycling.
What other applications do extremozymes have? Beyond PET recycling, extremozymes have applications in pharmaceuticals, cosmetics, food processing, nutraceuticals, and bioremediation. Cold-active extremozymes from Antarctica, for example, drive reactions at low temperatures — reducing energy costs in food and pharmaceutical manufacturing. Acid-stable extremozymes from the Río Tinto are also studied for biomining — using microorganisms to extract metals from low-grade ores.
What is the Nagoya Protocol and why does it matter for this research? The Nagoya Protocol is an international agreement governing access to genetic resources — including microorganisms collected from nature — and the fair sharing of benefits that arise from their use. For EXPLORA, it means that every organism collected from the Río Tinto or Antarctica must be sampled legally, with appropriate permits and documented benefit-sharing agreements. This legal framework ensures that the communities and countries whose environments host these organisms share in any commercial value that the research generates.
How does enzymatic PET recycling fit into the circular economy? Enzymatic PET recycling breaks plastic down into its original building blocks — terephthalic acid and ethylene glycol — which can be used to make new, virgin-quality PET. This creates a true closed loop: waste plastic becomes raw material for new plastic, without loss of quality and without the energy and chemical costs of conventional recycling methods. Extremozymes PET recycling is, therefore, a direct contribution to the circular bioeconomy goals at the heart of the EU’s Horizon Europe research programme.
