Researchers discover first plasticizing microbe

Bacteria decomposes PET plastic almost completely in a few weeks

PET bottles are usually barely biodegradable, but researchers have now discovered a microbe that can. © Filippo Vicarelli / freeimages
Read out

PET as a Favorite Food: For the first time researchers have discovered a microbe that effectively attacks a plastic and decomposes almost completely. In about six weeks, the bacterium Ideonella sakaiensis can completely degrade a PET film. It uses two previously unknown enzymes to break the plastic in two steps into its basic building blocks. For the first time, this discovery opens up the opportunity to biodegrade PET, according to the researchers in the journal "Science".

We use plastic to dig the earth: more than 300 million tons of plastic are produced worldwide every year, including around 50 million tons of polyethylene terephthalate (PET). This plastic is found mainly in plastic bottles, but also in packaging of all kinds. The problem with this: PET and Co are hardly biodegradable. They are therefore still decades later as plastic waste and microplastic in oceans, waters and even as micro residues in drinks, honey and salt.

Completely decomposed after six weeks

But now, for the first time, Shosuke Yoshida of the Kyoto Institute of Technology and his colleagues have discovered a bacterium that can degrade PET. They tracked down the microbe after they had carefully searched 250 samples of PET waste for growing bacteria and then continued to grow selected species on PET film.

A microbial community that contained the bacterium Ideonella sakaiensis proved to be particularly effective: "The PET film was severely damaged and was almost completely degraded after six weeks at 30 degrees, " report Yoshida and his colleagues. "The bacteria decomposed the PET surface at a rate of 0.13 milligrams per square centimeter per day. 75 percent of the carbon from the PET was converted to CO 2. "

The newly discovered bacteriuria and its enzymes could help to recycle the vast quantities of PET-M ll. Michal Ma &

Special enzymes ensure effective degradation

As it turned out, the bacterium Ideonella sakaiensis adheres to the PET surface and then attacks the plastic with the help of the previously unknown enzyme PETase. This breaks up the chemical bonds in the plastic. The degradation products of this reaction are taken up by the microbe and cleaved by a second selective enzyme (MHETase) into the basic building blocks ethylene glycol and terephthalic acid. display

Ultimately, the microbe also decomposes these chemical building blocks and releases the rest as CO 2, as the researchers report. This degradation process is so effective that the bacterium can cover its entire energy and nutritional needs from PET alone.

"Groundbreaking discovery"

"The discovery of this bacterium is groundbreaking for a number of reasons, " commented Biochemist Uwe Bornscheuer of the University of T bingen in an accompanying article. "Until now, very few enzymes have been known that show very little activity in the degradation of PET." Another crucial factor is the bacterium's ability to effectively attack the smooth PET surface.

The newly discovered microbe could be used purposefully to degrade PET waste in an environmentally friendly manner. Knowledge of the enzymes involved also opens up new ways of recycling plastics. One could develop methods to isolate the PET building block terephthalic acid and reuse it for the synthesis of PET. "This would undoubtedly represent a significant environmental relief, since the use of Erd l for the production of this plastic could be omitted, " said Bornscheuer.

So far, it has been puzzling how and why these bacteria have developed their two highly specific enzymes. Because PET has only been around in the environment for around 70 years this is an extremely short time for an evolutionary adaptation to this new food source. If Ideonella sakaiensis had newly developed its enzymes during this time, this would be an example of an unusually rapid evolution. (Science, 2016; doi: 10.1126 / science.aad6359)

(Science / University Greifswald, 11.03.2016 - NPO)