Microbes found that can digest plastic in freezing temperatures

In recent years, the search for organisms capable of breaking down plastic has become increasingly important, both for environmental and economic reasons. 

While several such microorganisms have been discovered, one major challenge in applying their plastic-degrading enzymes at an industrial scale is the required high operating temperatures – usually above 30°C. 

This necessity for heating not only adds to the overall costs but also undermines the goal of achieving a carbon-neutral solution. However, a group of Swiss scientists may have found a way to tackle this issue by focusing on cold-adapted microbes, whose enzymes can function effectively at lower temperatures.

In search of cold-weather plastic eaters

Researchers from the Swiss Federal Institute WSL turned their attention to high-altitude regions in the Alps and the polar areas, where they hoped to discover microorganisms capable of degrading plastic at cooler temperatures. 

The findings, recently published in the journal Frontiers in Microbiology, highlight the potential of these cold-adapted microbes to revolutionize the plastic recycling industry.

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

The research team collected samples from 19 strains of bacteria and 15 strains of fungi found growing on plastic litter in Greenland, Svalbard, and Switzerland. The plastic litter from Svalbard was primarily sourced during the Swiss Arctic Project 2018, where students participated in fieldwork to observe the effects of climate change firsthand. 

Meanwhile, Swiss soil samples were taken from the summit of the Muot da Barba Peider (2,979 m) and the valley Val Lavirun, both located in the canton of Graubünden.

Surprising results from the study

The scientists cultivated the isolated microbes in single-strain cultures in a laboratory, under dark conditions and at 15°C. Using molecular techniques, they identified that the bacterial strains belonged to 13 genera within the phyla Actinobacteria and Proteobacteria. The fungi strains were classified into 10 genera within the phyla Ascomycota and Mucoromycota.

The experts then performed a series of assays to screen each microbial strain for its ability to digest non-biodegradable polyethylene (PE), biodegradable polyester-polyurethane (PUR), and commercially available biodegradable mixtures of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA).

Although none of the strains were able to digest PE after 126 days of incubation, 56% of the strains, comprising 11 fungi and eight bacteria, managed to break down PUR at 15°C. Furthermore, 14 fungi and three bacteria were found to be capable of digesting the plastic mixtures of PBAT and PLA. 

Nuclear Magnetic Resonance (NMR) and a fluorescence-based assay confirmed that these strains could break down the PBAT and PLA polymers into smaller molecules.

“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 Dr. Rüthi.

The most efficient performers were two uncharacterized fungal species belonging to the genera Neodevriesia and Lachnellula, which could digest all tested plastics except for PE. Interestingly, the researchers observed that the ability to break down plastic depended on the culture medium for most strains, with each strain reacting differently to the four media tested.

Potential side effects resulting from this ability

One question that arises is how these microbes evolved to digest plastic, given that plastics have only been around since the 1950s. 

Dr. Beat Frey, senior scientist and group leader at WSL, explained: “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 to their resemblance to the plant polymer cutin.”

While the study focused on digestion at 15°C, the researchers have yet to determine 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 Dr. Frey.

The next challenge for the scientists is to identify the specific plastic-degrading enzymes produced by these microbial strains and optimize the process to obtain large amounts of proteins. 

Further modification of the enzymes might be necessary to improve properties such as protein stability, ultimately leading to the development of cost-effective and environmentally friendly plastic recycling methods.

By successfully demonstrating that these cold-adapted microbes can break down plastics at lower temperatures, this groundbreaking research opens the door to more cost-effective and environmentally friendly plastic recycling processes. 

As global plastic pollution continues to escalate, the development and implementation of such innovative solutions are critical to mitigating its detrimental impact on ecosystems and human health.

More about microbes that can digest plastics

Microbes that can digest plastics are garnering significant interest due to their potential to address the growing plastic pollution crisis. These organisms produce enzymes capable of breaking down plastic polymers into smaller molecules, which can then be further degraded or utilized as a carbon source by other microorganisms. 

Researchers are exploring the use of these plastic-degrading microbes for various environmental and industrial applications, including waste management and recycling processes.

There are several notable examples of plastic-digesting microbes discovered so far:

Ideonella sakaiensis

Discovered in 2016, this bacterium can break down PET (polyethylene terephthalate), a common plastic used in bottles and packaging materials. The bacterium produces an enzyme called PETase, which can break down PET into its monomers, allowing the bacterium to use the plastic as an energy source.

Aspergillus tubingensis

A fungus that was found to degrade polyurethane, a plastic commonly used in foams, adhesives, and coatings. The fungus secretes enzymes that break down the polyurethane, enabling it to access and utilize the carbon within the plastic.

Pseudomonas putida

A bacterium capable of breaking down polyurethane, which has been genetically modified to improve its plastic-degrading abilities. The modified strain can metabolize the plastic more efficiently, offering potential for industrial applications.

Pestalotiopsis microspore

A fungus discovered in the Amazon rainforest that can degrade polyurethane even in anaerobic (oxygen-free) environments, making it particularly interesting for breaking down plastics in landfill settings.

Waxworms (Galleria mellonella) and mealworms (Tenebrio molitor)

Though not microbes, these larvae can digest plastics like polyethylene and polystyrene, respectively. The larvae host gut bacteria that produce enzymes capable of breaking down the plastic polymers, turning them into simpler compounds.

While these discoveries are promising, there are still challenges to overcome before plastic-digesting microbes can be effectively used for large-scale plastic waste management. 

These challenges include optimizing enzyme efficiency, scaling up the process to industrial levels, ensuring the complete breakdown of plastic byproducts, and addressing potential ecological and health impacts.

Scientists continue to search for novel plastic-degrading microbes and enzymes in diverse environments, such as the deep sea, Arctic regions, and high-altitude alpine areas. 

By better understanding the plastic-degrading capabilities of these organisms, researchers aim to develop innovative strategies to tackle plastic pollution and create more sustainable waste management practices.

More about global plastic pollution

Global plastic pollution is a growing concern due to its detrimental impacts on both the environment and human health. The increasing production and consumption of plastic products, combined with inefficient waste management practices, have resulted in large amounts of plastic waste accumulating in various ecosystems, including oceans, rivers, soil, and air.

Impact on the environment:

Wildlife

Marine and terrestrial animals can become entangled in plastic debris or mistakenly ingest it, often leading to injury, impaired mobility, or death. Ingestion of plastics can also lead to the blockage of digestive systems, malnutrition, and starvation.

Ecosystem disruption

The accumulation of plastic waste in ecosystems can disrupt natural habitats, alter food chains, and affect species diversity. Microplastics, which are tiny plastic particles, can also be ingested by smaller organisms like zooplankton, making their way up the food chain and impacting larger species.

Chemical pollution

Plastics can leach harmful chemicals, such as bisphenol A (BPA) and phthalates, into the environment. These chemicals can accumulate in the tissues of organisms, leading to hormonal imbalances, reproductive issues, and other health problems.

Transport of invasive species

Plastic debris can serve as a vector for the transport of invasive species, which can outcompete native species and disrupt ecosystems.

Impact on humanity:

Human health

Microplastics and associated chemicals can enter the human food chain through the consumption of contaminated seafood, drinking water, or agricultural produce. The long-term health effects of ingesting microplastics and their associated chemicals are not yet fully understood, but they could potentially lead to hormonal imbalances, immune system issues, and other health problems.

Economic costs

Plastic pollution can have significant economic consequences, affecting industries such as tourism, fishing, and shipping. The costs associated with clean-up efforts, waste management, and loss of biodiversity can also burden local and national economies.

Climate change

The production, transportation, and disposal of plastics contribute to greenhouse gas emissions, exacerbating climate change. Additionally, the breakdown of plastics in the environment can release carbon dioxide, further contributing to global warming.

Addressing plastic pollution requires a combination of strategies, including reducing plastic production and consumption, improving waste management practices, promoting recycling and the use of biodegradable alternatives, and developing innovative solutions such as plastic-digesting microbes. 

By taking a multifaceted approach to tackle plastic pollution, it is possible to mitigate its impact on the environment, wildlife, and human health, and work towards a more sustainable future.

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