Newly discovered Arctic microbes may make recycling plastics carbon-neutral

These microbes can digest plastic at low temperatures.
Loukia Papadopoulos
Plastic trash pile
Could Arctic microbes help solve our plastics problem?

Claudio Schwarz/Unsplash  

Organisms that can digest plastic are all the rage as they help in the removal of pollution in our environment. However, currently available models only work at temperatures above 30°C, requiring a heating process that is not carbon-neutral. 

To solve this problem, scientists from the Swiss Federal Institute WSL looked for specialist cold-adapted microbes whose enzymes work at lower temperatures.

This is according to a press release by the institution published on Wednesday.

“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,” said the first author of the new study Dr. Joel Rüthi, currently a guest scientist at WSL. 

“These organisms could help to reduce the costs and environmental burden of an enzymatic recycling process for plastic.”

The researchers sampled 19 strains of bacteria and 15 fungi growing on free-lying or intentionally buried plastic in Greenland, Svalbard, and Switzerland. 

They then used a suite of assays to screen each strain for its ability to digest sterile samples of non-biodegradable polyethylene (PE) and the biodegradable polyester-polyurethane (PUR) as well as two commercially available biodegradable mixtures of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA).

None of the strains were able to digest PE, but 19 (56%) of the strains were able to digest PUR at 15°C, while 14 fungi and three bacteria were able to digest the plastic mixtures of PBAT and PLA.

“It was very surprising to us that we found that a large fraction of the tested strains was able to degrade at least one of the tested plastics,” said Rüthi.

Optimum temperatures

Now, Rüthi et al. still need to uncover the optimum temperature at which the enzymes of the successful strains work.

“But we know that most of the tested strains can grow well between 4°C and 20°C with an optimum at around 15°C,” said in the statement last author Dr. Beat Frey, a senior scientist and group leader at WSL.

“The next big challenge will be to identify the plastic-degrading enzymes produced by the microbial strains and to optimize the process to obtain large amounts of proteins. In addition, further modification of the enzymes might be needed to optimize properties such as protein stability.”

The research is published in Frontiers in Microbiology.

Study abstract:

Increasing plastic production and the release of some plastic into the environment highlight the need for circular plastic economy. Microorganisms have a great potential to enable a more sustainable plastic economy by biodegradation and enzymatic recycling of polymers. Temperature is a crucial parameter affecting biodegradation rates, but so far microbial plastic degradation has mostly been studied at temperatures above 20°C. Here, we isolated 34 cold-adapted microbial strains from the plastisphere using plastics buried in alpine and Arctic soils during laboratory incubations as well as plastics collected directly from Arctic terrestrial environments. We tested their ability to degrade, at 15°C, conventional polyethylene (PE) and the biodegradable plastics polyester-polyurethane (PU; Impranil®); ecovio® and BI-OPL, two commercial plastic films made of polybutylene adipate-co-terephthalate (PBAT) and polylactic acid (PLA); pure PBAT; and pure PLA. Agar clearing tests indicated that 19 strains had the ability to degrade the dispersed PU. Weight-loss analysis showed degradation of the polyester plastic films ecovio® and BI-OPL by 12 and 5 strains, respectively, whereas no strain was able to break down PE. NMR analysis revealed significant mass reduction of the PBAT and PLA components in the biodegradable plastic films by 8 and 7 strains, respectively. Co-hydrolysis experiments with a polymer-embedded fluorogenic probe revealed the potential of many strains to depolymerize PBAT. Neodevriesia and Lachnellula strains were able to degrade all the tested biodegradable plastic materials, making these strains especially promising for future applications. Further, the composition of the culturing medium strongly affected the microbial plastic degradation, with different strains having different optimal conditions. In our study we discovered many novel microbial taxa with the ability to break down biodegradable plastic films, dispersed PU, and PBAT, providing a strong foundation to underline the role of biodegradable polymers in a circular plastic economy.