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12 March, 2016

Newly-discovered bacterium can break down, metabolize plastic

According to a group of biologists in Japan, the newfound species — named Ideonella sakaiensis 201-F6 — breaks down the plastic by using two enzymes to hydrolyze poly[ethylene terephthalate], or PET.

PET is a condensation polymer used in plastic that is highly resistant to biodegradation. It is industrially produced by either terephthalic acid or dimethyl terephthalate with ethylene glycol.

To date, very few species of fungi – but no bacteria – have been found to break down this polymer.

The Japanese team, led by Dr. Kohei Oda from the Kyoto Institute of Technology and Dr. Kenji Miyamoto from Keio University, collected 250 samples of PET debris and screened for bacterial candidates that depend on PET film as a primary source of carbon for growth.

They identified Ideonella sakaiensis 201-F6, which could nearly completely degrade a thin film of PET after six weeks at a temperature of 86 degrees Fahrenheit (30 degrees Celsius).

Further investigation identified an enzyme, ISF6_4831, which works with water to break down PET into an intermediate substance, which is then further broken down by a second enzyme, ISF6_0224.

By screening natural microbial communities exposed to PET in the environment, we isolated a novel bacterium, Ideonella sakaiensis 201-F6, that is able to use PET as its major energy and carbon source,” the scientists explained.

When grown on PET, this strain produces two enzymes capable of hydrolyzing PET and the reaction intermediate, mono(2-hydroxyethyl) terephthalic acid.”

Both enzymes are required to enzymatically convert PET efficiently into its two environmentally benign monomers, terephthalic acid and ethylene glycol.”

Remarkably, ISF6_4831 and ISF6_0224 seem to be highly unique in their function compared to the closest related known enzymes of other bacteria, raising questions of how these plastic-eating bacteria evolved.

The discovery is reported in the journal Science.

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