NATURE is taking up the fight against pollution with the evolution of a bacterium that can break down plastic.
Japanese researchers collected samples of soils and wastewater contaminated with plastics in a hunt for microorganisms capable of degrading the PET (polyethylene terephthalate) drinks bottles and food packaging that litter the environment.
Around 56m t of PET was produced worldwide in 2013 but only around only 50% is collected for recycling, says the World Economic Forum. The research team describes the accumulation of plastics in the environment as a global concern, and says microorganisms with the natural capabilities to degrade PET could help with environmental remediation and be used in industrial fermentation to recycle waste plastics.
After screening the bacteria in their samples, the team found a promising candidate – a species of Ideonella that naturally produce enzymes that break down PET. The bacteria attach to the plastic using hair-like appendages and then secrete two enzymes that together break down the PET into the industrial precursors – terephthalic acid and ethylene glycol – used to produce the polymer.
While the bacteria are quicker than other biological agents, including enzymes from a fungus shown to degrade PET, the process remains slow. It took the bacteria six weeks at 30?C to fully degrade a piece of plastic smaller than a postage stamp. And the team reported it took even longer to break down the highly-crystallised form of PET used in drinks bottles.
Study author Kenji Miyamoto from Keio University described the work as “just the initiation”, acknowledging it will take a long time to resolve the many issues needed before it finds application.
Mike Neal, the chairman of the Committee of PET Manufacturers in Europe is not optimistic that a biological recycling system will find commercial use to replace or augment the mechanical processes commonly used to recycle PET. “I expect that a biodegradation system would require a similar engineering process to chemical depolymerisation and as such is unlikely to be economically viable,” he told the Guardian.
While depolymerisation by chemical rather than purely-biological routes is technically feasible, large-scale adoption of depolymerisation for PET has been hindered by processing costs.
Writing a comment piece on the research, Uwe Bornscheuer of Greifswald University in Germany said he was encouraged that in the 70 years since PET was first produced, microbes in nature have evolved to degrade plastics and expects more will be found if other researchers follow the Japanese team’s lead.
Catch up on the latest news, views and jobs from The Chemical Engineer. Below are the four latest issues. View a wider selection of the archive from within the Magazine section of this site.