The enzyme discovered that breaks down PET in less than a day

 German chemists have discovered a highly efficient enzyme that breaks down PET, one of the most used types of plastic in the world, in record time.

Christian Sonnendecker and his colleagues at the University of Leipzig identified the enzyme, along with several others, in a compost pile.

The plastic-eating enzyme could make biological recycling of PET (polyethylene terephthalate) possible much faster than previously thought possible. It was named PHL7.

Bacteria naturally use enzymes to break down plant parts and feed themselves. It has also been known for some time that some enzymes, so-called polyester-cleaving hydrolases, can also degrade plastics. For example, the enzyme LCC, discovered by Japanese researchers, is considered a particularly effective "plastic eater" - there are also fungi that degrade PET.

What distinguishes the new enzyme identified now is its speed of action.

In the experiments, the researchers added PET to containers with an aqueous solution containing the newly identified PHL7 or the well-known LCC, the previous leader in PET decomposition. Then they measured the amount of plastic that had degraded in a given period of time and compared the values ​​to each other.

The result: Within 16 hours, PHL7 caused the PET to decompose by 90%; at the same time, LCC achieved a degradation of only half of that, 45%.

"Therefore, our enzyme is twice as active as the gold standard among the polyester cleavage hydrolases," Sonnendecker stressed. "For example, PHL7 broke a plastic container - the kind used to sell grapes in supermarkets - in less than 24 hours."

The researchers found that a single enzyme building block is responsible for this above-average activity. Where other previously known polyester cleavage hydrolases contain a phenylalanine residue, PHL7 has a leucine. 

Biological recycling of PET has advantages over conventional recycling methods, which are primarily based on thermal processes, where plastic waste is melted down for reuse. These processes are highly energy-intensive and the quality of the plastic declines with each recycling cycle.

Enzymes, on the other hand, only require an aqueous environment and a temperature of 65 to 70 degrees Celsius to do their job. Another advantage is that it breaks down PET into its terephthalic acid and ethylene glycol components, which can be reused to produce new PET, without loss of quality, resulting in a closed-loop. So far, however, the biological recycling of PET has only been tested by a pilot plant in France.

The German team is now carrying out experiments for the degradation of PET bottles using the enzyme - compared to fruit and another packaging, typically "crystalline", PET bottles have additives that make their degradation more complicated.

Source:Article: Low Carbon Footprint Recycling of Post-Consumer PET Plastic with a Metagenomic Polyester Hydrolase