We have already discovered a number of tiny life forms capable of eating plastic, but their ability is often limited by the need for high temperatures, typically over 30°C. This heat requirement requires significant energy and is not exactly friendly to our planet. However, an innovative solution may lie in a different set of microbes that prefer cooler climates.
A team of Swiss scientists thought they had a good idea where to look for these unique cold-loving microbes – in the lofty peaks of their home country or the icy extremes of the North and South Poles. Their interesting discoveries were published in Frontiers in Microbiology.
We have identified new microbial species from plastic-laden soils in mountainous and polar regions that can break down ecological plastics at a cool 15°C, explained study leader Dr. Joel Rüthi. These life forms have the potential to reduce the cost and environmental impact of enzyme-based plastic recycling processes, he said.
The research team discovered 19 bacterial and 15 fungal species living on plastic waste in Greenland, Svalbard and Switzerland. Plastic from Svalbard was collected during the Swiss Arctic Project in 2018, when students contributed to the effort as part of their climate change fieldwork. Soil samples from Switzerland were obtained from both a high peak and a valley in the Graubünden region.
Back in the lab, these microbes were cultured in the dark at 15°C. Advanced techniques were used to classify them, with bacteria covering 13 groups in two large families, while fungi spread across 10 groups in two large families.
The scientists then evaluated each species in terms of its ability to break down different types of plastic. None of them managed to break down PE, a non-biodegradable plastic, even after 126 days. However, more than half managed to break down PUR, a biodegradable plastic, at 15°C. Certain fungi and bacteria have also managed to break down two types of commercially available biodegradable plastics, PBAT and PLA.
It was quite a surprise to find such a significant number of species capable of breaking down at least one of the plastic types, Rüthi admitted.
Two new species of fungi proved to be the most capable decomposers of plastics, able to decompose all tested plastics with the exception of PE. Interestingly, the study found that the plastic degradation ability of these microbes was affected by their growth conditions, with each species responding differently to each of the four different conditions.
So how did these microbes acquire the ability to break down plastic? After all, plastics only entered the scene in the 1950s.
Many microbes, especially fungi that cause plant diseases, can produce various enzymes capable of breaking down plant cell walls. These enzymes can target plastic polymers because they resemble a type of plant polymer, explained Dr. Beat Frey, Senior Scientist and Group Leader.
Still, there is work to be done. The team only tested at 15°C, so the optimal temperature for these plastic-eating microbes remains unknown.
Most of the species we tested seem to grow well between 4°C and 20°C, with the ideal temperature probably being around 15°C, Frey noted.
The next step is to identify the specific enzymes these microbes use to break down plastic and refine the process to make large quantities of these proteins. We may also need to modify the enzymes to increase their stability, he added.
Basically, these scientists discovered microbes in cold regions with the ability to break down certain types of plastic. This is an exciting prospect because it could make plastic recycling more efficient and cheaper.
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