Scientists have identified around 400 species of fungi that can break down petroleum – or plant-based – plastics, allowing them to be used to make new materials.
The discovery comes at a critical time, as governments and businesses around the world face inefficiencies, high costs and technical limitations that have put recycling rates at an all-time low. Along with other naturally-sourced tools such as bacteria and insects, future composting and recycling facilities could utilize fungi to degrade plastic and even help make new plastic.
What is plastic eating fungus?
What are commonly referred to as “plastic-eating fungi” are certain species of fungi that microbiologists say can break down popular plastics such as polyurethane and polyethylene. Polyurethane is used in many consumer goods such as clothing, insulating foam, and equipment. Polyethylene, often used in food packaging, is the most commonly used plastic in the world.
It's not entirely clear why fungi are so good at this task. They don't necessarily chew plastic as a food source, as is the case with some bacteria. One possible explanation: Fungi have found a way to exploit these materials. For example, these microbes can stick to plastic temporarily in the wild because they tend to survive longer than many natural materials and repel water—a rare trait in nature. Plastics in the wild offer “a different set of properties that are explored and utilized by microorganisms,” making them very different from the substances they inhabit, said Irina Druzhinina, a senior research leader at the Royal Botanic Gardens, Kew in England.
How do plastic-eating fungi work?
Researchers have observed how some species of fungus can devour various types of petroleum-sourced polymers, or the long chains of carbon and hydrogen atoms that often make up plastic. Plastic-eating fungi start by releasing enzymes, or proteins that speed up chemical reactions, to degrade these polymers. Various types of enzymes secreted by fungi can break down polymers into smaller units called monomers. However, how could they devour ingredients that were only mass produced after World War II?
In nature, some fungi degrade organic materials such as dead plants and animals, so they developed the skills to break down polymers with a structure somewhat similar to that found in plastic. It turns out that a group of enzymes that have long been used by fungi to break down lignin, a natural polymer found in the cell walls of most plants, work well in degrading mass-produced plastics such as polyethylene (PE) and polyvinyl chloride (PVC). The same appears to be true for another plant-degrading enzyme called esterase, which can help fungi feed on polyethylene terephthalate (PET) and polyurethane (PUR) plastics.
What types of plastic-eating fungi?
While researchers have discovered nearly 400 types of fungi that can break down plastic, certain types of fungi have attracted a lot of attention for their unique and efficient abilities.
Pestalotiopsis microspores
The mushroom that started it all. Early work on the genus Pestalotiopsis sent scientists down a rabbit hole of plastic-degrading fungi. In 2011, Yale University scientists announced that they had discovered that several fungi of the genus Pestalotiopsis convert polyurethane plastic (PUR) into organic materials in a laboratory environment. Two species can survive on a pure PUR diet in a setting without oxygen—meaning that they can get to work in oxygen-free landfills, where this type of plastic quickly accumulates and can take decades to dissipate. Pestalotiopsis fungi can also feed on plastic suspended in liquids, suggesting they could be dispersed into the ocean to feed on plastic pollution. The species Pestalotiopsis microspora does a really great job of breaking down PUR: Within two weeks and degrading it completely.
Pleurotus ostreatus
Commonly called oyster mushrooms, these mushrooms are a delicacy for us humans—but they can also chew through plastic efficiently. In early 2023, a team of Nigerian researchers announced that Pleurotus ostreatus and its cousin Pleurotus pulmonarius successfully degraded polyethylene terephthalate (PET), a highly durable and difficult to degrade plastic that is one of the most widely used worldwide (often incorporated into fabrics). and food packaging).
P. ostreatus was also found to be able to break down plastic mixtures in diapers and sanitary napkins containing polyethylene and polypropylene polymers. This is important because it is often difficult to recycle items containing various types of plastic. In addition to conventional types of plastic, research shows that P. ostreatus can be released effectively on plant-based plastics and emit by-products such as carbon dioxide and water.
Schizophyllum commune
In 2014, Austrian designer Katharina Unger announced a great idea: A device that could digest plastic waste and turn it into edible material. Working with scientists at Utrecht University in the Netherlands, Unger aims to feed plastic to P. ostreatus and a species of fungus called Schizophyllum commune to help them grow into delicious food.
Scientists have shown how S. commune, which grows on dead wood on every continent (except Antarctica), can destroy plastics such as polyethylene and synthetic polymers called phenolic resins thanks to its ability to chew through wood.
Aspergillus tubingensis fungus
This moldy fungus belongs to a genus with several promising candidates for plastic colonization. A 2017 study reported that soil-sourced Aspergillus tubingensis at a waste dump in Pakistan could completely degrade polyurethane into smaller pieces within two months. Relatives of A. tubingensis also have some impressive skills. After treating the polymer with heat or UV light, A. terreus reduced polypropylene samples by 25 percent over a 90-day period in the laboratory, according to a study published in early 2023.
Is this a realistic solution to plastic pollution?
Plastic-eating fungi aren't the answer to our waste problem—at least, not yet. Currently, molds work quite slowly and have only been proven to work with a few types of polymers. And just because things have worked in some tightly controlled laboratory conditions doesn't mean that mold is a sure-fire solution for fighting plastics in the wild or in industrial facilities. Scientists typically work with simplified versions of these polymers, but the products we use and throw away every day also contain chemical additives such as hardeners, so it's not clear how mold would work on these other materials.
What needs to happen for this to become part of the recycling process?
For this to work in existing recycling processes, the technique needs to be made faster and more efficient. Researchers are working to isolate the plastic-eating enzymes produced by fungi, along with other natural tools found in fungi and other microorganisms, and some are trying to engineer them to speed up the process.
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