Scientists from the Swiss Federal Institute WSL have found microbes that can digest plastic at 15ºC in a possible breakthrough for the recycling industry.
The microbes have been found in regions with near-polar temperatures, such as the Alps and the Arctic.
Scientists were previously aware of other types of microorganisms that are able to digest plastic. However, when the enzymes that make this possible were applied at an industrial scale, they typically only work at temperatures above 30°C.
The higher temperatures meant that money and energy would need to be spent heating the organisms, which is costly and carbon-intensive. In contrast, the newly-discovered microbes can digest plastic in temperatures as low as 15ºC.
“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 researcher Dr Joel Rüthi. “These organisms could help to reduce the costs and environmental burden of an enzymatic recycling process for plastic.”
Rüthi and colleagues sampled 19 strains of bacteria and 15 of fungi growing on free-lying or intentionally buried plastic in Greenland, Svalbard, and Switzerland.
The plastic litter from Svalbard had mostly been collected during the Swiss Arctic Project 2018, where students did fieldwork to witness the effects of climate change. The soil from Switzerland had been collected on the summit of the Muot da Barba Peider (2,979m) and in the valley Val Lavirun, both in the canton Graubünden.
The scientists let the isolated microbes grow as single-strain cultures in the laboratory in darkness and at 15°C and used molecular techniques to identify them.
The results showed that the bacterial strains belonged to 13 genera in the phyla Actinobacteria and Proteobacteria, and the fungi to 10 genera in the phyla Ascomycota and Mucoromycota.
None of the strains were able to digest non-biodegradable polyethylene (PE), even after 126 days of incubation on these plastics. But 19 strains (56 per cent), including 11 fungi and eight bacteria, were able to digest biodegradable polyester-polyurethane (PUR) at 15ºC, while 14 fungi and three bacteria were able to digest the plastic mixtures of polybutylene adipate terephthalate (PBAT) and polylactic acid (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.
The team’s next big challenge will be to identify the plastic-degrading enzymes produced by the microbial strains and to optimise the process to obtain large amounts of proteins.
The researchers’ findings have been published in the journal Frontiers in Microbiology.
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