Newly discovered cold-adapted microbes digest plastic at low temperatures

 

Swiss scientists have discovered new cold-adapted microorganisms that can degrade different types of plastic at temperatures lower than currently required. The discovery is the first step towards developing a more cost-effective, industrial-scale method that could rid the planet of plastic pollution.

There’s a great need to reduce plastic pollution on our lands and in our oceans. In 2020, annual global plastic production reached 367 megatons; and it continues to rise.

Already, several microorganisms that "eat" plastic have been discovered. These bacteria and fungi produce enzymes that break down the plastic, but when these enzymes are expanded to an industrial scale, they usually only work at temperatures above 86 °F (30 °C). Maintaining this temperature can be costly in terms of money and carbon neutrality.

The potential for using cold-adapted microorganisms to biodegrade plastics has rarely been studied. Thankfully, a team of Swiss scientists knew exactly where to look for such microorganisms. Heading to the alpine and Arctic regions of Greenland, Svalbard, and Switzerland, they sampled 19 strains of bacteria and 15 fungi found on discarded or intentionally buried plastic.

The scientists let the microorganism samples grow in the lab as single-strain cultures, in the dark and at a temperature of 59 °F (15 °C). They were then identified. The scientists found that the bacterial strains belonged to the phyla Actinobacteria and Proteobacteria and the fungi to the phyla Ascomycota and Mucoromycota.

Each of the strains was assayed to assess its ability to digest non-biodegradable polyethylene (PE) and biodegradable polyester-polyurethane (PUR), as well as two commercially available biodegradable mixtures of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA).

The scientists found that at 59 °F, more than half (56%) of strains – 11 fungi and eight bacteria – digested PUR, and 14 fungi and three bacteria digested PBAT and PLA. None of the strains could digest PE, even after 126 days spent on the plastic.

The award for best plastic eater was shared between two uncharacterized fungal species in the genera Neodevriesia and Lachnellula, which devoured all the plastics except PE.

The scientists found that most strains’ ability to digest plastic depended on the culture medium used. The next steps will be determining the optimal working temperature for these microorganisms and identifying the enzymes they use to break down plastic.

“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 enzymes,” said Beat Frey, one of the study’s co-authors. “In addition, further modification of the enzymes might be needed to optimize properties such as their stability.”

The study was published in the journal Frontiers in Microbiology.

Source: Swiss Federal Institute for Forest, Snow and Landscape Research WSL