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PET broken down by newly discovered enzyme

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Researchers have identified an enzyme that could help to manage the pollution of PET plastic, which is damaging to both land and marine environments.

  • Polyethylene terephthalate (PET), the basic commodity polymer used in the manufacture of plastic bottles, clothes and more, is known to globally contaminate marine and terrestrial environments.
  • Major plastic companies could be exposed to $20-100 billion in liabilities and litigation costs by the next decade if they do not act soon to reduce their environmental impact.
  • Around 80 enzymes derived from fungi or bacteria that can act on plastic have been discovered, this is the first from the deep sea. New, nature-based solutions to man-made pollution challenges could be one of the most exciting new areas for development. 

A new study involving scientists from Kiel University, the University of Hamburg and the Heinrich-Heine-University Dusseldorf have completed a microbial study that has shown for the first time, using microorganisms from the deep sea, that polymers such as PET are continuously degraded by an enzyme.

Professor Ruth Schmitz-Streit’s research group found that the enzyme, found by a sequence-based metagenome search, is derived from a non-cultivated, deep-sea Candidatus Bathyarchaeota archaeon.

Structurally, the enzyme differs significantly from those previously discovered. For example, it has the ability to degrade both very long-chain PET molecules, known as polymers, and short-chain PET molecules, known as oligomers, which means that degradation can be continuous.

The paper was published in the journal Communications Chemistry, where the research team explored both biotechnological applications and the high relevance of biogeochemical processes in the ocean and on land.

UN is working towards a global plastics treaty to address pollution.

In a historic decision at the fifth United Nations Environment Assembly in March 2022, all 193 UN Member States decided to end plastic pollution and negotiations on a binding legal agreement by 2024 are underway. It will be based on a comprehensive approach that addresses the full life cycle of plastic, which could include both binding and voluntary measures.

It is based on the recognition that the rapidly increasing levels of plastic pollution represent a serious global environmental issue affecting the environmental, social, economic and health dimensions of sustainable development. Under a business-as-usual scenario and in the absence of necessary interventions, the amount of plastic waste entering aquatic ecosystems could nearly triple from some 9-14 million tonnes per year in 2016 to a projected 23-37 million tons per year by 2040.

In just 30 years it is believed that fish in the ocean will be outnumbered by pieces of plastic. This issue is exacerbating the triple environmental crises of climate change, nature loss and pollution. Exposure to plastics harms human health and potentially affects fertility, hormonal, metabolic and neurological activity, while open burning of plastics contributes to air pollution.

With the treaty in process, and increasing focus on corporate impact on the environment, business as usual is no longer an option. Companies are going to need to address their plastics manufacture, use and disposal or be penalised for a failure to act.

In its latest report, Turning off the Tap: How the world can end plastic pollution and create a circular economy, UNEP explores the solutions that could realise that goal. These are a mixture of reuse, recycle and reorient and diversify.

Why does this discovery matter?

Accelerating the market for plastics recycling by ensuring that recycling becomes a more stable and profitable venture could reduce the amount of plastic pollution by an additional 20% by 2040. This will require adequate availability of feedstock that can be recycled and that recycled materials can compete on a level playing field with virgin materials, the researchers noted.

When it comes to PET plastics, it is a clear, strong, lightweight and theoretically 100% recyclable plastic. It’s not single use, an important factor has the world is increasingly seeing single-use plastic bans in fact, one came into force in the UK on 2 October 2023.

The challenge is that recycling PET is not straightforward. Not only are recycling rates relatively low, it is easy for PET to be contaminated with other materials, such as food and drink, which can make it difficult to recycle. PET can be made in a variety of colours, which can also make it difficult to recycle. And of course, as it is used in the recycling process, the quality can degrade over time, limiting its recyclability.

Biotech potential

The researchers say this breakthrough has potential applications in biotechnology, particularly for marine and terrestrial plastics. PET46 shares similarities with an enzyme called ferulic acid esterase, which is involved in the degradation of lignin in plant cell walls.

Given the structural similarities between lignin and PET, the PET-degrading enzymes discovered in the study could have implications for composting wood in forest soils and other biogeochemical processes related to PET degradation.

Importantly, PET46 has shown to be more efficient at higher temperatures compared to other PET-degrading enzymes. This finding opens up possibilities for the development of more effective enzymatic processes for PET plastic recycling and biodegradation.

The biochemical properties of PET46 therefore make it a very interesting enzyme both for marine and terrestrial plastics and for biotechnology. Compared to the best-characterized PET-degrading enzymes from bacteria and composting plants, PET46 is more efficient at 70 degrees Celsius than these reference enzymes at their respective optimum temperatures.

“Our data contribute to a better understanding of the ecological role of deep-sea archaea and the possible degradation of PET waste in the sea,” said Professor Ruth Schmitz-Streit, head of the Molecular Biology of Microorganisms working group at the Institute of General Microbiology (IfAM) and member of the research priority area Kiel Marine Science (KMS) at Kiel University.

The research was part of the PLASTISEA project, led by Professor Ute Hentschel Humeida of the GEOMAR Helmholtz Center for Ocean Research in Kiel. The study was a collaboration between Dr. Jennifer Chow from the University of Hamburg and Dr. Pablo Pérez-Garcia, a research assistant in Professor Ruth Schmitz-Streit’s group at Kiel University.

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