Tiny organisms like bacteria and fungi have brought us plenty of life-saving tools over the last century, including antibiotics, vaccines, and gene-editing technology. Now, scientists see another innovative use for these micro-creatures: Munching on plastic to curb pollution.
Each year, we rack up over hundreds of millions of tons of plastic waste globally, and much of which ends up in the ocean. Plastic production is only predicted to grow, so to combat the mounds of toxic trash piling up around the globe, scientists want to recruit microorganisms living everywhere from the seas to the Arctic that have developed a hunger for the stuff.
What bacteria can break down plastic?
After first picking up on hints in the 1970s,1 researchers have since discovered a nifty trait in certain microorganisms: They use enzymes, or proteins that speed up chemical reactions, to degrade some types of plastics and turn them into simple nutrients.2 This is particularly impressive: Humans and many creatures in the wild struggle to destroy and reuse plastic, because its long chains of carbon atoms are tough to break apart. And one item can contain multiple types of plastic, further complicating the process.
So far, scientists have pinpointed more than 400 species with the potential ability to weaken plastic’s chemical bonds.3 These species are often detected in water environments, landfills, and plastic refineries. But scientists are just getting started, according to Helge Niemann, a professor of biogeochemistry at the Royal Netherlands Institute for Sea Research. “We have no clue how many microbes might be out there that can degrade plastic,” he says.
Out of the hundreds of teeny plastic-eating species identified so far, scientists have taken special interest in certain heavy-hitters. These include bacteria in the groups called Rhodococcus, Bacillus, Streptomyces, and Penicillium (some of which gave us the miracle antibiotic penicillin). Some microorganisms even seem to target specific kinds of plastic.4
Japanese researchers announced in 2016 that they found the bacteria Ideonella sakaiensis at a PET bottle recycling facility.5 The bacteria seems to rely on this material, which is commonly used in packaging and textiles, as its primary carbon and energy source. Since then, teams around the world have taken a shot at engineering its intriguing enzymes, dubbed PETase and MHETase, to work better in industrial facilities.The former turns PET plastic into several substances including mono (2-hydroxyethyl) terephthalate, or MHET.
Then the aptly-named MHETase enzyme converts MHET into ethylene glycol and terephthalic acid, or the building blocks of PET—somewhat like separating a PB&J sandwich back into, well, peanut butter and jelly. The leftovers could be turned into valuable substances, like ethanol or bioplastics.6 But this work is still in its early stages.
What are the limitations of Ideonella Sakaiensis?
The magic enzymes in this microbe tend to work pretty slowly on PET—usually requiring a few days—but they can be genetically tweaked to speed things up. When a team of scientists created a model of the bacteria to understand how it evolved, they accidentally engineered it to munch on PET more efficiently. Now, researchers around the world are working on ways to ramp up its performance and prepare it for prime time.
In January 2023, biochemists with Niemann’s lab made history by becoming the first to show that bacteria can digest plastic and turn it into products such as carbon dioxide.7 The team set up an experiment to mimic seawater conditions and demonstrated that Rhodococcus ruber, a bacteria that has entered the spotlight in recent years for its plastic-nomming abilities, may be out there degrading around 1% of plastic annually in soil and water.8 They do this by forming a film containing substances such as proteins and sugar-like compounds. Then the bacteria converts the plastic into energy and carbon dioxide.9
Are plastic-eating bacteria a solution to ocean plastic pollution?
Some researchers think that microbes have specifically evolved to eat plastic as it clogs up their ecosystems on land and out at sea. Scientists analyzed more than 30,000 enzymes that can break down 10 types of plastic and found higher concentrations of these enzymes in ocean depths with greater plastic pollution, according to a 2021 study.10
But not everyone agrees. Mass plastic production didn’t kick off until the 1950s, says Irina Druzhinina, a senior research leader at the Royal Botanic Gardens, Kew, in England. It’s possible that certain traits, like the ability to munch on waxy leaves, just make microbes good at eating plastic. “It is far too recent, even for microbes,” she says. “Evolution of active enzymes takes longer than a few decades.”
It’s too early to say if bacteria could help solve the ocean plastic crisis, but researchers like Niemann of the Royal Netherlands Institute for Sea Research have made some exciting progress. Rhodococcus ruber, for example, could help solve a marine mystery: Around 2% of visibly floating plastic may disappear from the ocean’s surface every year, Niemann and his colleagues suggested, which could be in part due to destruction by bacteria.11
Alongside these marine bacteria, algae could also harness enzymes to break down plastics.12 However, microbes, algae, and the like can still take weeks or even decades to snack on plastic.13 With the amount in the ocean today, it would take generations to rid them of rubbish—and only if we stop adding to it.
“We’re still not sure what the impact of microbial degradation on plastic in the ocean is,” Niemann says. “My gut feeling is that, if we’d ever stop adding more plastic pollution to the ocean, after some time the system can regenerate itself.”
Even if we deploy all sorts of solutions like recycling, manufacturing plant-based plastics and wielding these plastic-hungry microbes, we still need to quit making new plastics to significantly reduce plastic pollution.
Can plastic-eating microbes really help with microplastics?
Studies have offered evidence that bacteria and algae can eat microplastics, or mini bits that measure less than 5 millimeters in length (around the size of a sesame seed). But scientists still need to figure out just how talented they are at this task. “They certainly can, but the efficiency is yet to be determined,” Druzhinina says. It’s also possible that microbes can release microplastics during their meals, she adds, but we don’t know to what degree it’s happening.
And as Niemann points out, we also can’t neglect nanoplastics—particles that are even tinier than microplastics, measuring less than a micron—that may prove even more harmful to the environment and our bodies.
Overall, it’s too early to know what exactly is up in the plastisphere, a term researchers coined in the last few years to describe the organisms taking up residence on plastics in the environment. “Environmental microbiology is in its infancy, and the microbiology of the plastisphere is a newborn,” Druzhinina says. “I think the fate of microplastics and their long-term effects on the environment is probably one of the least-understood areas.”
Are there side effects of plastic-eating bacteria?
It’s too soon to tell whether deploying plastic-eating microrganisms could have any deleterious impacts on the environment. And we won’t know until and unless they scale up in industrial facilities. For that to happen, labs need to perfect engineering the plastic-craving enzymes or wielding the entire organisms themselves. In the end, it’s possible that microbes or their enzymes could spit out additional microplastics, and facilities may still need to use chemical or UV treatments before this step.
Why is temperature important for plastic-eating bacteria?
Many plastic-eating bacteria can only do their thing at very specific temperature ranges because they have adapted to work in specific environments. Studies have shown that many microbes can only feast on plastic in lab environments around 68 degrees Fahrenheit or higher, which could require a lot of heat and energy to maintain at future microbe-powered composting facilities.
Microorganisms adapted to live in chilly locales could offer a more practical solution. In March 2023, a team from Switzerland announced they had found microbes from the Arctic that could snack on biodegradable plastics at cooler temperatures. The creatures worked well at breaking down plastics at 59 degrees Fahrenheit. But this research remains in the early stages—the scientists still need to tinker with the enzymes these bacteria produce to see if they can be wielded in industrial facilities.
- Biodegradation of polystyrene, poly(metnyl methacrylate), and phenol formaldehyde, Applied and Environmental Microbiology, Sep. 1979 ↩︎
- Biological degradation of plastics and microplastics: A recent perspective on associated mechanisms and influencing factors, Microorganisms, May 2023 ↩︎
- Phylogenetic distribution of plastic-degrading microorganisms, mSystems, Jan. 2021
- The Plastisphere – Uncovering tightly attached plastic “specific” microorganisms, PLoS One, Apr. 2019 ↩︎
- A bacterium that degrades and assimilates poly(ethylene terephthalate), Science, Mar. 2016 ↩︎
- Biodegradation of waste PET, EMBO Reports, Nov. 2019 ↩︎
- A stable isotope assay with 13C-labeled polyethylene to investigate plastic mineralization mediated by Rhodococcus ruber, Marine Pollution Bulletin, Jan. 2023 ↩︎
- Genome-based exploration of Rhodococcus species for plastic-degrading genetic determinants using bioinformatic analysis, Microorganisms, Sep. 2022 ↩︎
- Effect of proteases on biofilm formation of the plastic-degrading actinomycete Rhodococcus ruber C208, Microbiology Letters, May 2013 ↩︎
- Plastic-degrading potential across the global microbiome correlates with recent pollution trends, Microbial Ecology, Oct. 2021 ↩︎
- Plastic photodegradation under simulated marine conditions, Marine Pollution Bulletin, Feb. 2021 ↩︎
- Nature’s fight against plastic pollution: Algae for plastic biodegradation and bioplastics production, Environmental Science and Ecotechnology, Oct. 2020 ↩︎
- Microbial degradation and valorization of plastic wastes, Frontiers in Microbiology, Apr. 2020 ↩︎