Scientists have discovered microbes eating plastic in cold environments, like Arctic soil and alpine slopes, a breakthrough that could help to address the pervasive problem of plastic pollution around the world, reports a new study.
Humans collectively throw out about 400 million metric tons of plastic every year, a number that is only expected to grow in the coming decades. This deluge of durable trash is negatively impacting ecosystems around the world, and may pose a threat to human health.
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A lot of this waste gets dumped into habitats and communities where it breaks apart into small fragments, called microplastics, that take centuries to biodegrade. Microplastics have been found virtually everywhere on Earth, including deep sea trenches, Antarctic snow, the air we breathe, and even in our blood.
Microbes are among the best tools that scientists are studying to fight this pollution because some of these tiny organisms can digest certain plastics using specially-adapted enzymes. However, those enzymes usually require balmy temperatures of around 30°C (86°F) to work their magic on plastics at an industrial scale. This threshold places heating demands on these emerging bioengineering technologies, making them more expensive and less environmentally friendly.
Now, scientists led by Joel Rüthi, an environmental microbiologist at the Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, have discovered a host of cold-weather microbes in the Arctic and the Alps that can break down certain plastics at much lower temperatures of 15°C (59°F).
Rüthi and his colleagues have been studying the impacts of plastic pollution on microbes in pristine cold-weather environments for years, which revealed that some species seemed to use plastics as an energy source. Their new findings confirm that “microorganisms from high-alpine and polar regions are efficient producers of plastic-degrading enzymes and thereby may contribute to future efforts for an environment-friendly circular plastic economy,” according to a study published on Wednesday in Frontiers in Microbiology.
“We discovered a remarkably big diversity of microorganisms inhabiting high-alpine and Arctic soils in recent years,” explained Rüthi in an email to Motherboard. “Many of these microbes are completely unknown and we still don’t know a lot about their lifestyles and their abilities. From genetic analyses we expect that many could be very interesting for biotechnological purposes. Making this huge metabolic potential accessible was another motivation of our research group.”
“Cold-adapted microbes could, in future, help make plastic recycling more sustainable and cheap since the enzymes produced by these organisms work at lower temperatures and consequently would not need heating which saves energy,” he added.
Microbes can be found in almost every imaginable environment on Earth, from hyper-salty lakes, to radioactive fallout zones, to our own bodies. This versatility stems in part from their knack for exploiting unusual resources, such as methane, nuclear radiation, toxic waste, or the polymers found in plastics.
While many previous studies have identified plastic-digesting microbes, Rüthi and his colleagues searched for these organisms in overlooked cold environments. The team collected 34 microbial strains, including 19 bacteria and 15 fungi, from plastic material that had been left for several months at locations in Greenland, Svalbard, and the Swiss Alps. The microbes belonged to the Actinobacteria, Proteobacteria, Ascomycota and Mucoromycota families.
Back in the laboratory, the researchers exposed the microbes to a non-biodegradable plastic called polyethylene (PE) as well as three plastics designed to biodegrade on faster timescales. While none of the microbes could break down PE, about half were able to digest the other three plastics at 15°C.
“In earlier studies, where we buried the tested plastics in alpine and Arctic soils, we found that decomposition of biodegradable plastics was happening at 15°C,” Rüthi said. “However, the process was very slow in soil, and after five months at such low temperatures the plastic films were still largely intact.”
“Thus, we expected that there are plastic-digesting microorganisms living in these environments,” he added, though “we were surprised to find that a large fraction of the tested microbial strains was able to degrade at least one of the tested plastics.”
The results provide a roadmap for bioengineering new enzymes that can strip apart certain plastics at lower temperatures, potentially reducing the cost and carbon footprint of plastic recycling efforts in the future.
Given that plastic pollution is only getting worse, it will be essential to come up with sustainable ways to dispose of this resilient form of waste. To that end, Rüthi and his colleagues plan to build on their findings by continuing to study the superpowers of their wintery microbes.
“The next step would be to identify the enzymes produced by the microbial strains and to optimize their production,” Rüthi concluded. “From this we could learn more about important characteristics such as temperature optima and enzyme stability. This in turn will show whether the new enzymes could be used for an industrial application.”
