Claims that bacteria and enzymes can break down plastics are attracting increasing attention. But proving that the plastic itself has actually been degraded is far more difficult than it may seem. In a new article in Nature, NMBU researchers argue that inadequate experimental design, poorly characterized plastic materials and misinterpretation of analytical results have contributed to questionable conclusions in the scientific literature.
“Biological plastic degradation is a surprisingly challenging field of research. It can be relatively easy to obtain a signal that looks like degradation. The difficult part is proving that the signal actually results from cleavage of the plastic polymer itself,” says Professor Gustav Vaaje-Kolstad at the Norwegian University of Life Sciences (NMBU).
Polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and similar materials are used in enormous quantities, but are almost impossible to degrade biologically because they contain highly stable carbon–carbon bonds. In recent years, biotechnologists around the world have searched for microorganisms and enzymes capable of breaking down such materials, and numerous studies have reported promising results.
One challenge is that experiments can produce apparently positive results even when the plastic polymer itself has not been degraded. And when researchers are trying to solve a major problem, it can be easy to become overly influenced by positive results without asking sufficiently critical questions.
When positive results can be misleading
Vaaje-Kolstad began researching biological plastic degradation at NMBU in 2022 through a major project funded by the Research Council of Norway. Since then, the work has helped uncover several methodological challenges in the field.
In 2024, Anton Stepnov and colleagues showed in Nature Communications that they were unable to reproduce the results of two high-profile studies reporting enzymatic degradation of PE and PVC. At the same time, the researchers demonstrated how weaknesses in the analytical methods had contributed to the original, overly optimistic conclusions. The study also questioned previous reports that insect larvae can degrade PE. The results suggested that the larvae primarily chew and fragment the material without degrading the plastic polymer itself.
In another study published in 2025, Ronja Marlonsdotter Sandholm, a PhD candidate in the NMBU project, investigated a commercial PE material that is widely used in studies of biological plastic degradation. The bacteria grew on the material, but detailed analyses carried out in collaboration with the polymer research institute Norner in Porsgrunn showed that the bacteria were consuming short-chain hydrocarbons and oxidized compounds present in the material – not the plastic polymer itself.
“These experiences made it clear to us that the problem extends beyond a few individual publications,” says Vaaje-Kolstad. “Experiments on biological plastic degradation are inherently very demanding, and several of the methods commonly used in the field can produce misleading results if the substrate is not sufficiently well characterized and important control experiments are omitted.”
“If bacteria grow on something labelled ‘polyethylene’, it does not necessarily mean that they are eating polyethylene. We need to know exactly what the substrate contains before we can interpret the biology.”
The search will continue
Based on this work, Vaaje-Kolstad was invited by an editor at Nature to assemble an international group of experts to outline how biological plastic degradation can best be investigated, documented and verified.
Drawing on combined expertise in microbiology, enzymology, polymer science and oxidation chemistry, the researchers propose concrete guidelines in the Nature article for the characterization of plastic materials, appropriate control experiments and quantitative analyses.
For Vaaje-Kolstad, this is not about reducing interest in biological plastic recycling.
“The goal is not to slow down the search for plastic-degrading enzymes. Quite the opposite. Nature is highly adaptable, and there are probably microorganisms or enzymes that really can attack these highly resistant polymers. We biotechnologists will continue the search because we want to harness nature’s tools to help solve one of the major challenges of our time. But progress in the field depends on being confident that the effects we observe are actually caused by degradation of the plastic.”
Fact box
- The Nature Perspective is entitled “Assessing biological degradation of non-hydrolysable synthetic polymers”.
- The article is led by Anton Stepnov and Professor Gustav Vaaje-Kolstad from the Protein Engineering and Proteomics group at NMBU, together with an international group of experts in microbiology, enzymology, polymer science and oxidation chemistry.
- The authors include Shannon Stahl at the University of Wisconsin–Madison, Gregg Beckham and Allison Werner at the National Laboratory of the Rockies, Uwe Bornscheuer at the University of Greifswald, and Soo-Jin Yeom at Chonnam National University.
- Research on plastics has been part of NMBU’s sustainability initiative, launched in 2020.
- The NMBU research group is among Norway’s leading environments in enzyme technology. Its long-standing experience in high-level enzyme research has enabled the group to establish a strong position in biotechnological plastics research within a relatively short period. The group is led by Vincent Eijsink, who earlier this year received the prestigious European research award, the Novo Nordisk Foundation Prize in Biotechnology.
Sources/related links:
- Nature Perspective article: Assessing Biological Degradation of Non-Hydrolysable Synthetic Polymers
- https://www.nature.com/articles/s41467-024-52665-z
- https://academic.oup.com/ismej/article/19/1/wraf276/8381437
- https://novonordiskfonden.dk/en/news/he-solved-a-long-standing-enigma-in-biomass-science-vincent-eijsink-receives-the-2026-novonesis-biotechnology-prize/