Scientists discover microbes that can digest plastics at cool temperatures

In a potentially encouraging sign for reducing environmental waste, researchers have discovered microbes from the Alps and the Arctic that can break down plastic without requiring high temperatures. Although this is only a preliminary finding, a more efficient and effective breakdown of industrial plastic waste in landfills would give scientists a new tool for trying to reduce its ecological damage.

Scientists from the Swiss Federal Institute WSL published their findings this week in Frontiers in Microbiology, detailing how cold-adapted bacteria and fungus from polar regions and the Swiss Alps digested most of the plastics they tested — while only needing low to average temperatures. That last part is critical because plastic-eating microorganisms tend to need impractically high temperatures to work their magic. “Several microorganisms that can do this have already been found, but when their enzymes that make this possible are applied at an industrial scale, they typically only work at temperatures above [30 degrees Celsius / 86 degrees Fahrenheit],” the researchers explained. “The heating required means that industrial applications remain costly to date, and aren’t carbon-neutral.”

Unfortunately, none of the microorganisms tested succeeded at breaking down non-biodegradable polyethylene (PE), one of the most challenging plastics commonly found in consumer products and packaging. (They failed at degrading PE even after 126 days of incubation on the material.) But 56 percent of the strains tested decomposed biodegradable polyester-polyurethane (PUR) at 15 degrees Celsius (59 degrees Fahrenheit). Others digested commercially available biodegradable mixtures of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA). The two most successful strains were fungi from the genera Neodevriesia and Lachnellula: They broke down every plastic tested other than the formidable PE.

Plastics are too recent an invention for the microorganisms to have evolved specifically to break them down. But the researchers highlight how natural selection equipping them to break down cutin, a protective layer in plants that shares much in common with plastics, played a part. “Microbes have been shown to produce a wide variety of polymer-degrading enzymes involved in the break-down of plant cell walls. In particular, plant-pathogenic fungi are often reported to biodegrade polyesters, because of their ability to produce cutinases which target plastic polymers due [to] their resemblance to the plant polymer cutin,” said co-author Dr. Beat Frey.

The researchers see promise in their findings but warn that hurdles remain. “The next big challenge will be to identify the plastic-degrading enzymes produced by the microbial strains and to optimize the process to obtain large amounts of proteins,” said Frey. “In addition, further modification of the enzymes might be needed to optimize properties such as protein stability.”