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Synthetic Biology Technology

The very hungry bacteria; how plastic is on the menu for one microbe.

Landfill, Bio-Based World News“This could provide huge savings in the production of new polymer without the need for petrol-based starting materials…”

The PET Problem: Every year, plastic manufacturers splurge over 45 million metric tonnes of polyethylene terephthalate (PET) to make product packaging. PET containers can be found popularly in products such as sodas, water, juices, salad dressings, cooking oil, peanut butter, shampoo, liquid hand soap, mouthwash, pharmaceuticals, even tennis balls. Virtually all single-serving and 2-liter bottles of carbonated soft drinks and water sold in the U.S. are made from PET.

Many of these consumer goods, which sport the 1 recycle badge, however, are often overlooked by consumers when it comes to recycling, to the detrimant of global waste management. If not reyclced, PET deposits sit inert in landfill sites unable to be broken down by micro-organisms to biodegrade.

PETE Recycling Classification, Bio-Based World NewsWhile PET is still the most recycled kind of plastic in the USA (based on research by PETRA, the PET Resin Association), overall recycling rates are still only 31% nationwide. The European Union fares better, recycling over half of all PET products. Despite these efforts, tens of millions of metric tonnes of plastic end up in landfills each year. Once at landfill, the polymers strong ester bonds resist decomposition and become an eyesore on the natural environment. With an estimated 1 million metric tonnes of PET currently saturating pollutant landfills across the globe, a solution is needed to the PET problem.

To meet this international PET waste management crisis, a team of Japanese researchers led by Kohei Oda of Kyotos Institute of Technology and Kenji Miyamoto of Keio University, set out to discover if a microbe might be the answer to destroying these landfills of PET plastic waste.

The Hungry Bacterium:

The problem with PET is that while it can be chemically hydrolysed to its monomers, this process can be slow and often requires high temperatures and significant pressure which can cause further damage through process emissions. Funghi was also previously discovered that was found to break-down PET but is understood to be difficult to replicate on a global scale.

Oda and Miyamoto’s ground-breaking research team screened samples of 250 sediment, soil, wastewater, and activated sludge from a PET bottle recycling facility in Sakai, Japan. After careful analysis of microbial interaction with the waste, they singled out one particularly formidable bacterium that thrived on devouring PET films. The discovered microbe was named Ideonella sakaiensis in homage to the city of Sakai where they made the discovery.

Image credit Shosuke Yoshida, Bio-Based World News

Oda and Miyamotos group appears to be more efficient than all other previous solutions to the problem of PET deposits sitting inert in landfills. Their microbe carves up polymer at an impressively mild temperature of only 30C making it a sustainable, biological alternative.

The I. sakaiensismicrobe uses a series of enzymes to devour PET deposits. One enzyme, called PETase, breaks the plastics down into the intermediate mono(2-hydroxyethyl) terephthalic acid, or MHET. Another enzyme then hydrolyses the MHET into the monomers terephthalic acid and ethylene glycol.

The team of research scientists believe that this enzymatic machinery could one day remediate PET-contaminated environments or reclaim the plastics starting material components, which at present are derived from petroleum.

Uwe T. Bornscheuer, an enzyme catalysis expert at the University of Greifswald, explains the significance of this in a commentary that accompanies the discovery paper; This could provide huge savings in the production of new polymer without the need for petrol-based starting materials, he notes. Not only would the microbe remove waste efficiently, it would also result in manifest monetary savings across international markets.

Bales of PET bottles, Bio-Based World NewsThis promising waste-eating microbe is being further researched before being eventually released into landfill PET deposits to give the research project maximum impact on the global problem of waste management. At present, the bacterium prefers to dine on amorphous PET, rather than the crystalline PET used in most products, and the enzymes work too slowly to be used industrially at this stage. Author of the first study into this microbe, Shosuke Yoshida of Keio University, states that a PET pre-treatment that would enlarge the polymers amorphous areas would make waste more appetising for the bacterium. Also, he notes, in the future it might be possible to engineer these enzymes to make them faster and more practical as they face challenging levels of landfill PET.

The discovery couldnt come soon enough, with ever growing landfills of PET packaging piling up internationally, this one little microbe could be dining at the table of one of the worlds largest environmental issues. With some tweaking the scientists are confident that they can one day introduce the rubbish-devouring microbe and put it to work to devour the 1 million metric tonnes of PET that saturate pollutant landfills across the globe.


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