International researchers discover plastic-eating sea fungus

04 Jun 2024 --- Scientists have discovered a sea fungus capable of breaking down PE after being exposed to UV radiation from sunlight. The researchers, including Dutch marine microbiologists at the Royal Netherlands Institute for Sea Research (NIOZ), believe that many more plastic degrading fungi are living in deeper parts of the ocean. 

Published in the scientific journal Science of the Total Environment, the study spotlights the fungus Parengyodontium album, which lives together with other marine microbes in thin layers on plastic litter in the ocean.

The researchers revealed that the fungus is capable of breaking down PE particles, the most abundant of all plastics that have ended up in the ocean.

The NIOZ scientists worked with colleagues from Utrecht University, the Netherlands, the Ocean Cleanup Foundation and research institutes in Paris, France, Copenhagen, Denmark and St Gallen, Switzerland. 

“The finding allows the fungus to join a very short list of plastic-degrading marine fungi: only four species have been found to date. A larger number of bacteria was already known to be able to degrade plastic,” they highlight.

A plastic particle (red) is colonized by the marine fungus Parengyodontium album (Image credit: Annika Vaksmaa of NIOZ).Plastic in the wild
The researchers went to find the plastic degrading microbes in the hotspots of plastic pollution in the North Pacific Ocean. From the plastic litter collected, they isolated the marine fungus by growing it in the laboratory, on special plastics that contain labeled carbon. 

“These so-called 13C isotopes remain traceable in the food chain. It is like a tag that enables us to follow where the carbon goes. We can then trace it in the degradation products,” explains study lead author Annika Vaksmaa of NIOZ.

“What makes this research scientifically outstanding, is that we can quantify the degradation process.” 

In the laboratory, Vaksmaa and her team observed that the breakdown of PE by P. album occurs at a rate of around 0.05% each day. 

“Our measurements also showed that the fungus doesn’t use much of the carbon coming from the PE when breaking it down,” she details. “Most of the PE that P. album uses is converted into carbon dioxide, which the fungus excretes again.” 

Although carbon dioxide is a greenhouse gas, the researchers believe this process is not cause for concern. The amount released by fungi is “the same as the low amount humans release while breathing.”

Scouring depths for unknown fungi
The presence of sunlight is essential for the fungus to use PE as an energy source, the researchers found.

“In the lab, P. album only breaks down PE that has been exposed to UV-light at least for a short period of time. That means that in the ocean, the fungus can only degrade plastic that has been floating near the surface initially,” explains Vaksmaa. 

“It was already known that UV-light breaks down plastic by itself mechanically, but our results show that it also facilitates the biological plastic breakdown by marine fungi.”

As a large amount of different plastics sink into deeper layers before it is exposed to sunlight, P.album will not be able to break them all down. However, Vaksmaa expects that there are other, yet unknown, fungi out there that are degrading plastic in deeper parts of the ocean. 

P. album could be one among many other undiscovered types of oceanic fungi capable of breaking down plastic, the researchers posit.“Marine fungi can break down complex materials made of carbon,” she highlights. “There are numerous amounts of marine fungi, so it is likely that in addition to the four species identified so far, other species also contribute to plastic degradation.”

“There are still many questions about the dynamics of how plastic degradation takes place in deeper layers.”

Solution to plastic soup
Finding plastic-degrading organisms is an urgent mission. Every year, humans produce more than 400 billion kgs of plastic, and this is expected to have at least tripled by the year 2060, warn the researchers.

“Much of the plastic waste ends up in the sea: from the poles to the tropics, it floats around in surface waters, reaches greater depths at sea and eventually falls down on the seafloor.”

“Large amounts of plastics end up in subtropical gyres, ring-shaped currents in oceans in which seawater is almost stationary,” says Vaksmaa. “That means once the plastic has been carried there, it gets trapped there.”

“Some 80 million kg of floating plastic have already accumulated in the North Pacific Subtropical Gyre in the Pacific Ocean alone, which is only one of the six large gyres worldwide.”

In other biorecycling advances, Carbios and the Toulouse Biotechnology Institute, in France, are now working on a “next-generation enzyme” to break down plastic in a proposed “standardized enzymatic hydrolysis protocol.” The solution is slated for use in the “world’s first” PET biorecycling plant, scheduled for commissioning in 2025.

By Benjamin Ferrer