Is it true that microbes can break down plastic and clean up all the pollution?

This claim is uncertain. The role that microbes play in tackling plastic pollution is uncertain and still under investigation. However, their role in solving plastic pollution is likely to be limited. In lab studies, scientists have identified bacteria and fungi with the ability to biodegrade specific kinds of plastics under certain conditions. But this doesn’t mean microorganisms can clean up every type of plastic in every natural environment. Given the large quantities of plastics that are added to the environment each year, microbes won’t be able to keep up with the vast amounts of material. They could only make a small contribution to solving the problem

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Eco anxiety is of increasing concern and means that many people are seeking environmental news stories which offer hope. One powerful story concerns the potential of nature to evolve and “heal itself”. Take the oil spill of the Deepwater Horizon that not only polluted the Gulf of Mexico with hundreds of thousands of tons of crude oil, but large quantities of methane gas. Methane is a much stronger greenhouse gas than CO2, so the spill could have been a big issue for the climate. But the gas just vanished, to the surprise of many experts. It’s believed that bacteria cleaned it up. Wouldn’t it be great if something similar happened for plastic pollution? Could nature already be healing itself through the power of mighty microbes? Or could humans somehow “harness the power of these plastic-eating microbes” and turn it into “a game-changer in the fight against plastic pollution”?

Exciting and surprising questions like these make great content for media outlets and social influencers. So the discovery of a new microorganism with the ability to biodegrade plastic has good chances of featuring in the media. For example, the bacterium Ideonella Sakaiensis had its moment of fame in 2016. Ideonella can break down the plastic we know from bottles, polyethylene terephthalate (PET), and was found close to a bottle recycling facility in Japan. The following year, the fungus Aspergillus tubingensis from Pakistan got a place in the media spotlight, with its appetite for another plastic, the polyester polyurethane.

But we need to take a closer look to really understand the broader implications of those reports. How much potential do microorganisms really have when it comes to solving plastic pollution—what does the science say?

Only a small bite: A fungus with appetite for polyethylene

In 2024, a study led by Annika Vaksmaa from the NIOZ Royal Netherlands Institute for Sea Research made big headlines. Vaksmaa and her colleagues had isolated a marine fungus from trash collected in the North Pacific Garbage Patch: Parengyodontium album. They grew it in the lab and found that it was able to break down the plastic polyethylene. Polyethylene is used to make plastic bags, packaging and other household products. It is the most abundant plastic in the ocean and lighter than water, so it floats.

However, Parengyodontium album can only biodegrade plastics that have been exposed to UV radiation from the sunlight. And there are other kinds of plastics in the ocean. Some also float, like polypropylene, other kinds, like polyester, are denser than seawater and sink. The fungus won’t be able to tackle the waste deeper down in the dark layers of the ocean. It can only, so to say, take a small bite out of all the plastic waste in the oceans. When it does, it doesn’t make much use of the plastic: Parengyodontium excretes most of the carbon from the plastic as carbon dioxide.

Potential to spread: A fungus surviving on polyurethane

Most reports in journalistic media mention the limitations of microbes for solving plastic pollution. But they also take advantage of click-baity titles that over exaggerate the potential and generate excitement. Take the example of a Newsweek piece from 2014 titled “The Plastic-Eating Fungi That Could Solve Our Garbage Problem”.

In the article, Newsweek reports on the discovery of a fungus called Pestalotiopsis microspora found by Yale University students in the Ecuadorian Amazon in 2011. When grown in the lab and fed with the polyester polyurethane, it showed the ability to only subsist and grow on the carbon from the plastic, even in anaerobic conditions.

The professor who led the discovery, however, did “not believe there's enough in the study to warrant media coverage”. The Newsweek report juxtaposes his reluctance with other expert voices: experts who see the discovery as the beginning of a new kind of “mycoremediation”, where fungi help clean up our trash.

There’s a risk to Pestalotiopsis microspora: the organism’s potential for horizontal gene transfer. If released into the wild, the plastic-hungry fungus could pass on its abilities to other organisms, with potentially disastrous effects, Newsweek notes. So despite the title’s claim, the report’s author comes to much more skeptical conclusion—the title is classic and misleading clickbait.

What do the discoveries of plastic-degraders really mean?

Here’s another bit of information: In 2021, researchers from Chalmers University of Technology in Sweden screened DNA collected in the environment. Using computer models, they identified over 30,000 microbial enzymes that have the potential to biodegrade 10 different kinds of plastics: 18,000 in soil and 12,000 at sea. Enzymes are molecules produced by cells of living organisms that speed up chemical reactions — like breaking down plastics, for example. Specific enzymes are needed for each reaction. If there are so many enzymes with the potential to biodegrade common plastics, does that mean, that this is already happening in nature?

In 2022, a group of experts reviewed the scientific literature on microbial biodegradation of plastic—and was not convinced. The scientists led by Gavin Lear from the University of Auckland in New Zealand concluded that the “evidence for the microbial degradation of most plastic polymers in current circulation is lacking” and that microbes abilities were being overstated. Due to a lack of data, it’s still impossible to pinpoint the role of microbes in degrading plastics.

Plastics are a relatively recent addition to the environment, especially when viewed in the context of biological evolution. It can take thousands, if not millions, of years, for organisms to develop new phenotypes or classes of enzymes. So far, it appears that microbes are repurposing enzymes that originally evolved for other functions, such as breaking down plant biomass or lipids. Some of these enzymes show limited activity against plastics, and under controlled laboratory conditions with specialised instruments, we can detect this slow degradation. However, these enzymatic activities are still far too slow to have any meaningful impact on environmental plastic waste.

Victor Gambarini is running the database PlasticDB. It collects the species of microorganisms and proteins with plastic-degrading capabilities that have been reported in the scientific literature so far: Over 750 microbes and 200 proteins. Gambarini also examined the distribution of plastic-degrading microorganisms in the oceans more closely. “We know some microbes can break down certain plastics”, Gambarini explained in a recent opinion article. However, if microbes were actively degrading plastics in the environment, the researcher would expect higher concentrations of plastic-degrading microorganisms in areas with more plastic pollution. Surprisingly, Gambarini wrote, “our new study finds no clear correlation between plastic pollution levels and the production of plastic-degrading enzymes by marine microorganisms”.

It’s difficult to transfer results from the lab to nature

And biologist Martin Klinkhardt noted in an online article on the topic: “The ultimate effectiveness and efficiency of these enzymes remain largely unknown. Almost all the findings to date were obtained under optimized laboratory conditions at constant temperatures with a good supply of nutrients. This makes it quite difficult to transfer the results directly to nature, because the conditions there are quite unstable and vary over time and space.”

Another study found that there is a “low prevalence of known plastic degraders throughout most environments, except for substantial enrichment in riverine systems”.

Despite these caveats, visions of microbes as “nature’s new clean-up crew” and bacteria as “one of our most effective weapons in the war against plastic waste” remain attractive. Some already see “a fascinating future for waste disposal”, dreaming up “an army of mycelium chewing quietly and methodically through our plastic bags and foam coffee cups—and potentially even creating a new food source along the way. We could have our trash and eat it, too.”

Are plastic munching microbes over- or underrated?

“If plastic pollution were to cease today, it would likely take several generations for the existing plastic in the ocean to degrade,” Helge Niemann of the EU-funded VORTEX project says. The researchers concluded that while there is evidence for microbes that biodegrade plastics, they are quite slow, considering the growing amounts of plastic waste. They estimated the rate of ocean microplastic degradation at a few percent per year.”

In the long term this may reap benefits. However, to date we cannot say that nature will quickly “heal itself” and clean up plastic pollution. There are too many different kinds of plastics and chemicals ending up in different environments, from soils to sea. Most of the bacteria and fungi with the ability can only biodegrade certain plastics and chemicals in certain environments. And while plastics can end up anywhere, in the soil, rivers, lakes, the ocean and the air, not every microbe can live everywhere.

As long as we’re putting more and more plastics in to the environment, microbes will not be able to keep up. Over long timescales, nature might be able to convert some of the plastics, but this will not be the case in the short term. So, the most hopeful tale to combat the bad news is: We need to reduce the influx of plastics into the environment.

Sources

Expert check

Thanks to Victor Gambarini of the University of Auckland and, Helge Niemann from the Royal Netherlands Institute for Sea Research (NIOZ) for scientific fact-checking.

Updated on: October 22, 2024