Microbes across the land and ocean are evolving to degrade plastic

Microbes across the land and o...
Plastic pollution is widespread across the globe, and new research shows that microbes that can break it down are evolving to match it
Plastic pollution is widespread across the globe, and new research shows that microbes that can break it down are evolving to match it
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Plastic pollution is widespread across the globe, and new research shows that microbes that can break it down are evolving to match it
Plastic pollution is widespread across the globe, and new research shows that microbes that can break it down are evolving to match it

Five years ago, scientists digging through soil and sludge around a plastics recycling center in Japan discovered a bacterium that was feeding on the popular packaging material PET as an energy source, with help from a pair of purposely evolved enzymes. A fascinating discovery at the time, a new study has shown this to be part of a much wider trend in which such plastic-degrading enzymes are increasing in numbers and diversity in response to plastic pollution around the world.

Since that discovery in Japan in 2016, we have seen a couple of other interesting advances in this space. The initial hope was that by unearthing those enzymes that enabled the bacterium to quickly reduce PET plastic into environmentally benign building blocks, even more efficient versions could be engineered in the lab to form new weapons in the fight against plastic pollution.

In 2018, a group of scientists in the US built on this research to produce an engineered enzyme that could consume plastics with around 20 percent greater efficiency. That same team then developed an even more advanced version in 2020, which they described as a super-enzyme, that could digest plastic waste at six times the speed.

A range of enzymes with similar abilities have been uncovered, and new research by a team from Sweden's Chalmers University of Technology shows just widespread the phenomenon is. The researchers analyzed samples of environmental DNA sourced from hundreds of ocean and terrestrial locations around the world, using computer modeling to screen them for microbial enzymes with the potential to break down plastics.

This revealed a total of 30,000 enzymes with the potential to degrade 10 types of common plastics, with the scientists then cross-referencing this with official data on concentration of plastic pollution across different countries and oceans. It turned out that some of the locations with the highest amount of enzymes were the most heavily polluted areas, such as the Mediterranean Sea and South Pacific Ocean.

“Using our models, we found multiple lines of evidence supporting the fact that the global microbiome's plastic-degrading potential correlates strongly with measurements of environmental plastic pollution – a significant demonstration of how the environment is responding to the pressures we are placing on it,” says study author Aleksej Zelezniak.

The enzymes were found to be distributed widely across ocean and terrestrial locations, but with a few interesting insights. The team found higher concentrations of plastic-degrading enzymes at deeper levels in the ocean, indicating a connection with the greater concentrations of microplastics seen at these depths. Similarly, the land samples were found to contain many more phthalate-based plastic additive compounds, along with enzymes known to be capable of degrading them, indicating a connection between the two.

“Currently, very little is known about these plastic-degrading enzymes, and we did not expect to find such a large number of them across so many different microbes and environmental habitats. This is a surprising discovery that really illustrates the scale of the issue,” explains Jan Zrimec, first author of the study.

The mass production of plastic has skyrocketed from around two million tonnes annually to a staggering 380 million in the last seven decades or so, and around eight million tonnes wash into the ocean each year. While this has given microbes a sizable window to develop evolutionary responses to the waste in their environments, it would take a lot of highly efficient enzymes to eat away at the problem. But with significant findings like this, the scientists' playbook continues to expand.

“The next step would be to test the most promising enzyme candidates in the lab to closely investigate their properties and the rate of plastic degradation they can achieve," says Zelezniak. "From there you could engineer microbial communities with targeted degrading functions for specific polymer types."

The research was published in the journal mBio

Source: Chalmers University of Technology

Is this a case of "be careful what you wish for"? There are plenty of plastics in the environment that we do not want to degrade; think of plastic water pipes, sewer pipes, cable insulation, foundation materials, drainage pipe, the list is long. IF super-degrading enzymes are developed, they will undoubtedly help with plastic pollution, but they will also "go wild" meaning that ultimately they will spread everywhere and begin to degrade all of the plastic we wish to keep.
Maybe we are not in control of the planet after all. What a crazy idea.
And what happens when this bacteria interact with other lifeforms?
@Winterbiker yeah that's a good point. I can see a world where there has to be strict segregation between single use plastics and mechanical/structural plastics, once they get to eating the one, how to keep them from eating the other?
Just wondering if we could rid ourselves of plastic instead of engineering a bacterium? Are the bacterium smarter than us?
@Winterbiker It takes things like plastic bags 500 years to decompose now. Even if this speeds up significantly I don't think thicker structural plastics for things like drain pipes would be at any short term risk. The concentration of these enzymes are probably more common in places like landfills as well and even if we got to a place where plastic was eaten quickly we could still experiment with compounds and coat it in other materials to protect it. We still use wood as a building material and it gets reclaimed by nature exponentially faster than plastic so I'm not that worried about it.
If the growing enzymes conquer the discarded out-of-control plastics, then what will the hungry, out-of-control enzymes turn to next? Winterbiker has a serious point. And the commenters below should be generally more in charge of things, I think.
@Winterbiker, these microbes will cause decomposition, but there are ways to prevent (or at least delay) regular microbes causing decomposition of organic matter, so I would assume the same thing applies here.
didn't we have bio-degradable plastics in the 1980s already?