We already know there are microorganisms that can break down plastic. However, they can usually only do this at high temperatures, which would cost a lot of money in heating and would likely require fossil fuels to keep the temperature high. Now, a team of researchers found a way forward with a new type of microorganism.

A team from the Swiss Federal Institute WSL was looking at microbes in Greenland, Svalbard, and Switzerland when they came across some that could break down plastic at temperatures of 15 degrees Celsius. Previously, scientists only found microbes doing this at around 30°C, which means the finding could have a big impact on recycling.

“Here we show that novel microbial taxa obtained from the ‘plastisphere’ of alpine and arctic soils were able to break down biodegradable plastics at 15°C,” first author Joel Rüthi from WSL said in a media statement. “These organisms could help to reduce the costs and environmental burden of an enzymatic recycling process for plastic.”

Tackling plastic waste

For their study, the researchers sampled 19 strains of bacteria and 15 species of fungi growing on free-lying or intentionally buried plastic (in the ground for a year) in Greenland, Svalbard, and Switzerland. They let the isolated microbes grow as single-strain cultures in the lab in darkness and at 15 °C and used molecular techniques to identify them.

The bacterial strains belonged to 13 genera in the phyla Actinobacteria and Proteobacteria, and the fungi to 10 genera in the phyla Ascomycota and Mucoromycotina. The team tested these with various types of plastics, including polyethylene (PE), polyester-polyurethane (PUR), polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA).

None of the strains could digest PE, even after 126 days of incubation. However, over 50%, including 11 fungi and eight bacteria, could digest PUR at 15 °C, while 14 fungi and three bacteria were able to digest the plastic mixtures of PBAT and PLA. The team stated they were to be “very surprised” that many strains could degrade at least one type of the tested plastics.

The best performers were two uncharacterized fungal species in the genera Neodevriesia and Lachnellula. These could digest all of the plastics, except PE. The results also showed that the capacity of the fungi and bacteria to digest plastic depended on the culture medium, with each strain reacting differently to each of the four media tested.

“Microbes have been shown to produce a wide variety of polymer-degrading enzymes involved in the break-down of plant cell walls. In particular, plant-pathogenic fungi are often reported to biodegrade polyesters, because of their ability to produce cutinases which target plastic polymers due their resemblance to the plant polymer cutin,” lead author Beat Frey said.

Since the researchers only tested plastic for digestion at 15 °C, they don’t know yet what’s the best temperature at which the enzymes of the successful strains work. However, they are optimistic that they are capable of working at much lower temperatures, as the tested strains can actually grow between 4 °C and 20 °C. This could then be a big deal for plastic recycling.

Global plastic pollution has become a pressing issue, posing threats to the environment and human well-being. The surge in plastic production and consumption, coupled with ineffective waste management strategies, has led to the accumulation of substantial quantities of plastic waste across diverse ecosystems, such as oceans, rivers, soil, and even the air.

The study was published in the journal Frontiers in Microbiology.