Wood-munching fungi can break down common type of plastic

Fungi that typically decay hardwood trees have been found to break down polyethylene, a plastic used in shopping bags, food wrap and bottles.

Hardwood trees are notoriously resistant to decay. A small number of fungi, however, can attach to these trees and degrade the lignin, a strong polymer that is key to wood structure, in its trunks.

“Lignin is the hardest natural polymer on Earth,” says Renuka Attanayake at the University of Kelaniya in Sri Lanka. “If the fungi can degrade lignin, they must have a very strong battery of enzymes.”

Attanayake and her colleagues decided to investigate whether these fungi could be used to decompose polyethylene, one of the most abundant plastics on Earth.

The team collected small pieces of decayed hardwood from Dimbulagala dry zone forest reserve in Sri Lanka. In the laboratory, they isolated the fungi from the wood and identified 21 species.

Each of the fungi was incubated with sheets of low-density polyethylene between 28 and 30°C. They repeated this in the presence and absence of hardwood.

After 45 days, the team removed the polyethylene and examined how its physical properties had changed. The polyethylene weighed less after exposure to the fungi compared with before. This was the case both with and without wood, but more weight loss was observed in the absence of wood.

As well as showing that the fungi are able to break down polyethylene, the results also reveal that the fungi can adapt their metabolic behaviour depending on the environment.

“It seems that they can use diverse carbon sources and have the metabolic flexibility to use whatever is available,” says Attanayake.

These fungi could one day be used to tackle plastic pollution, which is a particularly large problem in lower-income countries like Sri Lanka, she says. Although polyethylene can be recycled, in some cases it may be preferable to remove the plastic from the environment.

“But it certainly is still in the early stage,” says Attanayake. She wants to conduct further tests on the properties of the fungi and find out if they can break down other materials.

Uwe Bornscheuer at Greifswald University in Germany says it will take much more work to harness the potential of these fungi. For starters, we don’t yet know which of the fungi’s enzymes are involved in the decay of polyethylene. “From my point of view, this is a very early start of a challenging and complex journey,” he says.