Microbes across the globe are evolving to eat plastic pollution

Tiny organisms around the world are evolving to eat plastic pollution, according to a new Swedish study.

Mass production of plastic has skyrocketed in the past 70 years, from approximately two million tonnes to around 380 million tonnes per year, with about eight million tonnes of plastic escaping into the world’s oceans annually, according to a release.

Researchers from Sweden’s Chalmers University of Technology analyzed environmental DNA samples from around the world and found the number of microbial enzymes with the ability to degrade plastic is growing in correlation to local levels of plastic pollutions, detailing their findings in a study recently published in the journal mBIO.

As plastics production has ramped up over several decades, researchers posit this has given the organisms sufficient time to evolve and respond to the plastic compounds in their environment.

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Researchers first compiled a dataset of 95 microbial enzymes already known to degrade plastic, such as those found in bacteria that live in landfills, and then looked for similar enzymes in environmental DNA samples taken by collaborating researchers from more than 200 locations around the world.

The study analyzed more than 200 million genes found in the DNA samples taken from the environment and found 30,000 enzymes that could degrade 10 different kinds of plastic. The study took care to prevent false positives that could arise by comparing the new enzymes to those found in the human gut, which contain no known plastic-degrading enzymes.

“Using our models, 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,” said study author Aleksej Zelezniak, in the release.

Approximately 12,000 of the new organisms were found in samples taken from 67 locations across oceans at different depths. Soil samples taken from 169 locations in 38 countries and in 11 different ecological habitats were found to contain 18,000 plastic-degrading enzymes.

Researchers found that the number of enzymes discovered in a sample area correlated to the amount of plastic pollution, for example, more plastic-degrading enzymes were found at lower levels in the ocean, indicating a connection to the greater level of microplastics that have been repeatedly observed deeper in the ocean, the release notes

The soil samples showed a higher concentration of phthalate-based plastic additive compounds, which are used in industrial processes to make plastics more durable and often leak into the environment during production, disposal and recycling. More enzymes that were able to degrade those specific types of plastic were found in the soil samples, indicating a connection.

Almost 60 per cent of the new enzymes discovered in the study did not fit into any previously categorized class of microbes.

“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. This is a surprising discovery that really illustrates the scale of the issue,” said lead study author Jan Zrimec in the release.

As the natural process for plastics to fully decompose in the environment is very slow, with a plastic PET bottle taking decades, the researchers believe their discovery of new microbial enzymes could be used to create more recycling processes.

“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.”