Microbes Are Evolving to Eat Plastic Pollution, Study Shows

The abundance of plastic waste on Earth is creating microorganisms that are capable of degrading it, new research shows.

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Millions of years ago, evolution turned tiny microbes into multicellular plants, animals, and humans. Now, evolution is turning them into something equally remarkable: environmentalists.

So finds a new study from researchers at Sweden’s Chalmers University of Technology. Published this month in the scientific journal mBIO, it found plastic waste is giving rise to a growing number of microbes that produce pollution-fighting enzymes. The enzymes, which can degrade various types of plastic, appear to be evolving in direct response to the accumulation of plastic pollution, the quantity of which has increased from approximately 2 million tons per year 70 years ago to approximately 380 million tons per year today.

“We found multiple lines of evidence supporting the fact that the global microbiome’s plastic-degrading potential correlates strongly with measurements of environmental plastic pollution — a significant demonstration of how the environment is responding to the pressures we are placing on it,” Aleksej Zelezniak, associate professor of systems biology at the Chalmers University of Technology, said in a news release.

To arrive at their conclusion, Zelezniak and his colleagues compiled a dataset of 95 microbial enzymes already known to degrade plastic, which are typically produced by bacteria in garbage dumps and other plastic dumping grounds. They then collected samples of environmental DNA from hundreds of locations across the globe, both on land and at sea, and used computer modeling to search for similar “plastic-eating” enzymes. Because no plastic-degrading enzymes have been discovered in humans, despite concerns about the ingestion of microplastics, they used samples of the internal human microbiome as a control for false positives. In total, they identified approximately 30,000 enzymes with the ability to degrade 10 major commercial plastics.

Nearly 60% of the identified enzymes were new to researchers, and environmental samples with the largest concentrations of enzymes were from highly polluted areas like the Mediterranean Sea and the South Pacific Ocean. Plus, more of the enzymes found on land were able to degrade plastic additives commonly found in soil, such as phthalates, which often leak during plastic production, disposal, and recycling. Among the ocean samples, meanwhile, enzymes were most prevalent at lower ocean depths, where microplastics accumulate in large quantities.

All of this suggests that microbes are continuing to evolve new plastic-fighting superpowers in response to their immediate environment.

“Currently, very little is known about these plastic-degrading enzymes, and we did not expect to find such a large number of them across so many different microbes and environmental habitats,” said Jan Zrimec, first author of the study and former post-doc in Zelezniak’s group, now a researcher at the National Institute of Biology in Slovenia. “This is a surprising discovery that really illustrates the scale of the issue.”

The natural process for plastic degradation is very slow. A typical plastic bottle, for example, will spend up to 450 years in the environment before it degrades. As such, the only solution to the plastic crisis is eliminating the creation of virgin plastic or significantly reducing it. Researchers are hopeful their work will eventually lead to the discovery of microbial enzymes that could be commercialized for use in recycling. If companies could use enzymes to rapidly break down plastics into their basic building blocks, the thinking goes, new products could be made from old ones, thereby reducing demand for virgin plastic.

“The next step would be to test the most promising enzyme candidates in the lab to closely investigate their properties and the rate of plastic degradation they can achieve,” Zelezniak said. “From there you could engineer microbial communities with targeted degrading functions for specific polymer types.”

Currently, only 9% of plastic waste in the United States is recycled each year, according to the World Wildlife Fund, which says plastic waste causes $8 billion in economic losses annually through negative impacts to the fishery, maritime, and tourism industries; harms more than 800 animal species; and endangers humans by posing a public health risk, decreasing fish stock, and contributing to climate change.

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  1. Zrimec, Jan, et al. "Plastic-Degrading Potential Across the Global Microbiome Correlates with Recent Pollution Trends." Mbio, vol. 12, no. 5, 2021, doi:10.1128/mbio.02155-21

  2. "The Lifecycle of Plastics." World Wildlife Fund, 2021.

  3. "Plastics." World Wildlife Fund,