Plastic-Degrading Enzymes May Be Increasing in Response to Pollution

One in every four organisms in the microbiomes they surveyed carries a plastic-degrading protein sequence

Large amounts of plastic trash like bottles in a channelized creek in Culver City, California.
Large amounts of plastic trash accumulated in Ballona Creek in Culver City, California. Citizens of the Planet via Getty Images

Microbial enzymes across the globe are evolving to degrade plastic, according to a new study. Scientists examined hundreds of samples taken from oceans and soils and found thousands of enzymes capable of degrading different kinds of plastic. The researchers behind the recent work say microbes have likely evolved in response to plastic pollution.

Plastic production has spiked in recent decades, increasing from 2 million tons in 1950 to 368 million tons in 2019. The researchers at Chalmers University of Technology in Sweden found that the number and type of enzymes matched the amount and type of plastic pollution in different locations. The study published in the journal of Microbial Ecology is the first large-scale study of bacteria’s plastic-degrading potential.

“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,” study co-author Jan Zrimec, who was a biologist at Chalmers University at the time of the research, says in a press release. “This is a surprising discovery that really illustrates the scale of the issue.”

In their study, the team first combed through databases of environmental DNA samples from soils and oceans around the world. Using computer modeling, they then looked for protein sequences that would likely break down plastic based on enzymes already known to have plastic-degrading abilities. The authors say one in every four organisms in the microbiomes they surveyed carries a plastic-degrading protein sequence, which the team describes as an enzyme homologue, meaning it behaves like an enzyme but may not technically be one, per Gizmodo's Isaac Schultz.

In the end, the scientists found over 30,000 enzyme "homologues" capable of degrading 10 different types plastic. Around 12,000 of those enzymes were found in samples from the ocean, gathered at various locations and depths, Brooke Migdon reports for the Hill. The team found higher concentrations of plastic-degrading enzymes in deeper areas of the ocean where there was more plastic pollution.

“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,” says Aleksej Zelezniak, study co-author and biologist at Chalmers University, in a statement. The work is a “significant demonstration of how the environment is responding to the pressures we are placing on it.”

Nearly 60 percent of the new enzymes the team found did not fit into any known enzyme classes, leading the authors to conclude that the area needs additional research. Because many plastics are difficult to recycle and end up polluting ecosystems, enzymes could potentially be used quickly to degrade plastics. By breaking down plastic into their building blocks, industries could reduce the need to manufacture new plastics, as new products could be made from old ones.

Microbial enzymes could help reduce the impact of plastic pollution on the environment, but they won’t solve the problem alone. With around 14 million tons of plastic entering oceans every year, scientists emphasize that we also need to reduce plastic demand and production. 

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