A new study from a team of scientists at Chalmers University in Sweden describes how microbes in soil and water may be evolving to eat plastic. The researchers found the evidence in DNA samples taken from the environment, which revealed some 30,000 unique enzymes that are capable of degrading 10 different types of plastics.
The researchers believe that as many as one in four of the organisms analyzed carried a plastic degrading protein sequence. The team describes it as an enzyme “homologue”, meaning it acts like an enzyme but has not yet been classified as such, according to Gizmodo. Interestingly, the number and type of enzymes the researchers discovered matched the amount and type of plastic pollution in different locations. Aleksej Zelezniak, a biologist and part of the Chalmers team, said that they found “multiple lines of evidence supporting the fact that the global microbiome’s plastic-degrading potential correlates strongly with measurements of environmental plastic pollution.”
The study is the first large-scale global assessment of the plastic-degrading potential of bacteria. “Currently, very little is known about these plastic-degrading enzymes, and we did not expect to find such a large number of enzymes across so many different microbes and environmental habitats,” study co-author Jan Zrimec said in a press release. The dramatic increase of plastic production in the past 70 years, from 2 million tons to 380 million tons a year, has given microbes time to evolve to deal with plastic, the researchers said.
To conduct the study, the team compiled a dataset of 95 microbial enzymes already known to degrade plastics. The team then looked for similar enzymes in existing environmental DNA samples taken by other researchers from 236 different locations around the world. The researchers ruled out potential false positives by comparing the enzymes initially identified with enzymes from the human gut, which is not known to have any plastic-degrading enzymes. Nearly 60% of the new enzymes did not fit into any known enzyme classes, which the scientists say suggests the molecules degrade plastics in ways that were previously unknown.
Soil samples taken from 169 locations in 38 countries and 11 different habitats contained around 18,000 new plastic degrading enzymes. About 12,000 of the new enzymes were found in ocean samples, taken at 67 locations and at three different depths. The results showed consistently higher levels of degrading enzymes at deeper levels, matching the higher levels of plastic pollution known to exist at lower depths. In the samples taken from soils, which typically contain more plastics with phthalate additives than the oceans, the researchers also found more enzymes that attack these chemicals.
Zelezniak says the next step is to test the most promising enzymes in the lab to measure their properties and the rate of plastic degradation the can achieve. “From there you could engineer microbial communities with targeted degrading functions for specific polymer types,” said Zelezniak. (Sources: Gizmodo, The Guardian)
