Science

Scientists discover garden fungi that can break down tough plastic in just 140 days

Nearly a third of the world’s plastic waste is polypropylene, a tough plastic used to make bottle caps and food containers that can take hundreds of years to degrade. But now scientists have harnessed two strains of fungi found in soils to break down lab samples of polypropylene in just 140 days.

The two mushrooms Aspergillus terreus And Engyodontium Albummade a meal of plastic in lab experiments: between 25 and 27 percent of samples were devoured after 90 days, and the plastic was completely broken down after 140 days, the researchers report.

The team of Australian scientists behind the study, led by graduate student Amira Farzana Samat, described their work as an “important stepping stone” in designing practical biological ways to deal with plastic waste.

“This is the highest degradation rate reported in the literature that we know of. [of] around the world,” Ali Abbas, a chemical engineer at the University of Sydney, told Australian Broadcasting Corporation technology reporter Danny Tran.

While this may be a speed record for fungi, plastic-munching bacteria recently discovered in a compost pile were able to break down 90% of PET, or polyethylene terephthalate, in just 16 hours. But a little healthy competition is good; this is how evolution works.

So far, more than 400 microorganisms have been shown to naturally degrade plastic, with fungi attracting attention for their versatility and ability to degrade all manner of synthetic substrates with a powerful concoction of enzymes.

“Recent studies suggest that some fungi can even degrade some of the ‘eternal chemicals’ like PFAS, but the process is slow and not yet well understood,” says microbiologist Dee Carter from the University of Sydney.

At the basic chemical level, plastics are a chain of carbon atoms adorned with different side chains that give each type of plastic its specific properties. Recycling plastics, in theory, should be as simple as breaking apart the repeating subunits that make up plastics and reassembling them into something new.

But there are so many different types of plastics that when they’re all mixed and mixed with other materials as waste, they’re virtually impossible to separate and recycle. Most plastic waste is either incinerated or landfilled.

“We need to support the development of disruptive recycling technologies that improve the circularity of plastics, especially technologies that rely on biological processes,” says Abbas.

Laboratory experiments showed that together the two fungi could decompose polypropylene pellets and thin films, as well as foil-coated polypropylene sheets.

Although researchers don’t yet know exactly how the fungi digested the plastic – this could be the subject of future research – the idea is that the fungi break down materials like plastic into simpler molecules which they can then absorb. or excrete.

As you can see in the image below, the mostly smooth plastic became riddled with marks as the fungi did their dirty work.

Microscopic images showing the plastic degraded by fungi (right) compared to the untreated sample (left). (Samat et al., npj Material degradation2023)

The method requires a pretreatment step with UV light, heat, or a chemical reagent, to weaken the waste so the fungi can attack. This step mimics the environmental conditions necessary for fungi to cling to and open plastics and is designed to make the degradation process more efficient.

Abbas says their method could be scaled up like any fermentation process, but adds that his team has yet to optimize the experimental conditions to work on an industrial scale. The method also does not replace efforts to reduce plastic waste, he says.

A common predictable limitation of plastic-crunching microbes is that they have difficulty degrading the more crystalline forms of plastic used in commercial products as well as other types of plastic waste.

Next steps for the researchers include building a benchtop prototype, testing modifications to speed up the process, and evaluating the economic feasibility and environmental impact of using their method on a commercial scale. .

However, there is often a bumpy road between experimenting on a lab bench and developing a market-ready product.

Last we heard back in 2015, researchers behind a prototype orb-shaped device called Fungi Mutarium – which turns plastic waste into a safe, edible product using two types of mushrooms – continued their work to speed up the process of decomposition.

More recently, scientists have been scrambling to find ways to make useful bioplastics from the air, create recyclable plastics from super glue instead of crude oil, and turn plastic polymers into liquid fuel.

These exciting discoveries will require a lot more work if they are to make a real dent in the vast amounts of rapidly accumulating plastic waste.

The research has been published in npj: Degradation of materials.

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