Identification of efficient plastic-feeding fungi in freshwater ecosystems

Lina Portman2 days ago

2 3 minutes read

The presence of plastics in our environment is an increasing burden on nature and our health. Scientists from the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) and the University of Potsdam have identified fungi isolated from freshwater ecosystems that can efficiently degrade plastic polymers made of polyurethane, polyethylene and tire rubber. Contrary to previous assumptions, no pretreatment of the plastics was necessary. The study was published in Science of the Total Environment.

Plastics made from polymers can persist in the environment for decades because they are not degraded, or are broken down very slowly, by bacteria in soil and water. As a result, research is underway around the world to find practical and sustainable ways to deal with plastic and rubber waste. The research team has now selected 18 strains of fungi and tested their ability to break down polyurethane, polyethylene and tire rubber. These are some of the most common plastics found in the environment. The results show that strains of Fusarium, Penicillium, Botryotinia and Trichoderma have a high potential for plastic degradation.

Mushrooms well suited to the “plastisphere”

In recent years, researchers have shown that there are microfungi capable of breaking down even complex polymers, making them suitable for bioremediation.

But why are mushrooms such good plastic recyclers? “Fungi produce enzymes capable of breaking down chemical compounds made up of many macromolecules, such as plastic. Additionally, they are well adapted to life in the plastic sphere thanks to their invasive growth forms and their ability to form biofilms and to interact with existing biofilms,” said IGB researcher Professor Hans-Peter Grossart, who led the study.

Scanning electron microscope analyses showed the team that the cell walls of some fungi deform when they colonize plastics. These are probably structural adaptations of the mycelia that allow them to colonize, for example, water-repellent polyurethane,” said Sabreen Samuel Ibrahim Dawoud, a doctoral student at IGB and first author of the study.

FT-IR spectroscopy to analyze changes in the microstructure of fungi and DOC analysis to determine their metabolic activity demonstrated that the initial enzymatic activity of fungi leads to the formation of intermediates that serve as a carbon and energy source for fungi by increasing the concentration of soluble organic carbon available for fungal growth. In this way, fungi are constantly creating new food for themselves through degradation,” said Sabreen Dawoud.

No pretreatment by UV light, ozonation or other chemical or thermal processes is required

The study also showed that fungi can degrade polymers without any pretreatment of the plastics and without adding sugars as an energy source.

To initiate microbial degradation of plastic polymers, many studies have first used UV light, ozonation, chemical oxidants, or thermal pretreatments to effectively oxidize plastic polymers and generate reactive functional groups before inoculating the polymer with mushrooms. These treatments were not used in this study and do not appear essential for fungal activity. However, it has not been studied whether such treatments would have modified the dynamics of the degradation process.

And they are the successful plastic eaters

Among the selected strains, strains of Fusarium, Penicillium, Botryotinia And Trichoderma have shown a particularly high potential for degrading polyethylene, polyurethane and tire rubber. Some of the terrestrial occurrences of these fungi are not yet very popular with humans: Fusariumfor example, is known in agriculture as a fungus harmful to cereals and corn. Botryotinia can also cause various plant diseases. Trichoderma The species are filamentous fungi that live all over the world in soil, in plants, in decaying plant remains or even in wood. They are important decomposers and interact with plants, other microorganisms and soil. Kind of species PenicilliumOn the other hand, play an important role in the production of penicillin and foods such as moldy cheese.

The researchers also tested whether certain types of fungi could only degrade certain types of plastic or rubber and which plastic was best degraded by the fungi. The result: polyurethane turned out to be the most degradable of all the plastics tested. “Knowledge of more efficient fungal strains, especially for the biodegradation of polyurethane, contributes to the development of concepts for large-scale recycling of plastic waste,” concluded Hans-Peter Grossart.