Mushrooms could be the solution to eliminate plastic waste

Enlarge Anton Petrus

Plastic is becoming a scourge on Earth. Not only are landfills full of them, but they have polluted our oceans so much that a tiny creature that apparently had microplastics in its diet has been named Eurythenes plasticus. Can we stop the spread of material that is accumulating faster than it could ever decay?

There could be an answer, and that answer is a mushroom. Researchers from the University of Kelaniya and the University of Peradeniya in Sri Lanka have discovered species of fungi capable of breaking down polyethylene, the same type of plastic used for bags, bottles, cling film, take away, etc. These fungi have one thing in common: they usually break down hardwood, which otherwise doesn't break down quickly. While hundreds of fungi and other microorganisms are known to break down various plastics, it was previously unknown that these particular hardwood-eating species could degrade polyethylene.

“Microbial biodegradation of plastics is a promising strategy for depolymerizing petroleum-based plastics into monomers or mineralizing them into carbon dioxide and water,” researchers said in a study recently published in PLOS ONE. The breakdown

How difficult can it be to decompose hardwoods such as ironwood or ebony? It's tough (pun intended somewhat) because the wood is held together by polymeric lignin, which is found in the cell walls of the wood and gives it its strength. Lignin is tough but can be broken down and depolymerized by the right enzymes.

When the research team discovered rotting dead hardwoods in a forest reserve, they became curious because these trees do not decompose easily. They collected samples of the mushrooms which they pulled from the wood and brought back to their lab. The mushrooms were then isolated by species, with each species placed in a different container and given pieces of hardwood and polythene sheets to feast on.

The team wanted to compare the plastic-eating abilities of fungal species and determine each species' production of an enzyme that breaks down lignin. The degree of deterioration of plastic and hardwood was determined by comparing the weight of these materials before and after exposure to fungi. In 45 days, the wood lost between just over 1 percent and nearly 36 percent of its weight. This weight loss occurred because the fungi broke down lignin and cellulose into products containing carbon dioxide.

The plastic also lost weight by being converted into simpler molecules by fungal enzymes over the same amount of time, losing nearly half of its mass. Polyethylene is generally a hydrophobic or water-resistant material, but it gradually loses this property as it degrades. It also becomes more fragile. As the fungi did their job, the polyethylene became more and more brittle and lost its ability to repel water.

The researchers also wanted to see what the mushrooms would do if they were given no wood and only plastic. It was possible that they ate less plastic without seeing their favorite food, because the wood probably activates their digestive enzymes. But what happened was rather surprising. "The most striking feature of the experiment was that all isolates showed higher [polyethylene] degradation in the absence of wood than in the presence of wood," the researchers said in the same study.

These fungi need carbon to survive. Although wood was their preferred carbon source, when it was not available, polyethylene provided an alternative. Their degradation of more plastic, when offered, showed that they were easily able to adapt metabolically and change their diet when there was no wood nearby.

Lignin and polyethylene have common chemical properties. When they used their Li...