Plastic straws

Swiss study shows microbes can degrade plastics at low temperatures

Microbes capable of functioning at 15°C could represent a breakthrough in the microbial recycling of plastics
25 May 2023 , Kerry Taylor-Smith

Swiss study is also an area of focus for researchers at University of Manchester, who say lack of standardisation across the UK plastics supply chain is preventing a circular economy

The use of plastic is expected to triple by 2050, but recycling rates are low, partly due to consumer confusion over what to recycle and how, and partly because scientists haven’t yet identified the most energy-efficient means of recycling.

Microbe-digesting bacteria have shown promise but often function at temperatures above 30°C, meaning their heat requirements make their use in industry expensive. Additionally, they are not carbon neutral.

However, a recent study from the Swiss Federal Institute WSL found 19 strains of bacteria and 15 strains of fungi which were able to degrade different plastics at just 15°C. These microbes were found growing on free-lying or intentionally buried plastic in Greenland, Svalbard, and Switzerland and were then grown as single-strain cultures in the laboratory in darkness at 15°C.

“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 first author, Dr Joel Rüthi. “These organisms could help to reduce the costs and environmental burden of an enzymatic recycling process for plastic.”

Researchers tested the microbes’ ability to degrade different types of plastic including non-biodegradable polyethylene (PE) and biodegradable polyester-polyurethane (PUR), plus two commercially available biodegradable mixtures of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA).

No strain could degrade PE, even after 126 days of incubation; however, 11 fungi and eight bacteria strains could degrade PUR at 15°C, and 14 fungi and three bacteria could degrade PBAT and PLA. Additionally, two uncharacterised fungal species could digest all the tested plastics except PE. The scientists only tested the microbes at one temperature, but they say it works well between 4°C and 20°C.

One of the study authors, Dr Beat Frey, a senior scientist said, “The 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. In addition, further modification of the enzymes might be needed to optimise properties such as protein stability”.

“Microbial-based strategies for molecular recycling of waste materials is an important part of our move towards more efficient use of resources and greater circularity.”

Microbial degradation is also a key area for researchers from the University of Manchester focusing on one of the most environmentally challenging plastics produced; polyethylene terephthalate (PET).

“Globally we create two billion tonnes of municipal waste each year, much of which is carbon-based and so disposal leads to significant greenhouse emissions,” said Dr Neil Dixon from the Sustainable Biotechnology at Manchester Institute of Biotechnology.

“In combination with an approach to prevent reduce, and recycle waste, it would be prudent for us to explore approaches that enable the re-use of the carbon, within these waste materials, earlier within the cycle before it is released as gas emissions. Microbial-based strategies for molecular recycling of waste materials, including plastics, is an important part of our move towards more efficient use of resources and greater circularity.”

Colleagues at Manchester also argue that the UK needs to rethink the current recycling system; they say a lack of standardisation across the plastics supply chain is preventing the UK from transitioning to a circular economy, and inconsistency in plastic packaging composition and messaging around recycling practices is causing confusion among consumers, resulting in just 44.4% of plastic waste generated being recycled in 2021.

A recent trial of their suggested ‘one bin’ system for all recyclable and non-recyclable plastic waste found almost a quarter of the items were flexible packaging materials, the most challenging for consumers to recycle, and that a large-scale standardised approach to recycling flexible plastics was critical to improving recycling rates.


Image credit: Shutterstock

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