Science News

Bacteria that can break down plastic

Thu, 10th Mar 2016

Chris Smith

Bacteria that can degrade PET, one of the most commonly used forms of plastic, have been identified by Japanese scientists.

Every year nearly 60 million tonnes of polyethylene teraphthalate or PET plastic products are made and consumed worldwide.

The substance crops up in drink bottles, clothes and packaging, and the plasticity, transparency and durability of the material make it an attractive manufacturing option.

However, its resilience to environmental degradation is a significant drawback leading to the accumulation of the plastic in seawater, sediments and landfill.

Animals taking in the particles can also concentrate the material up the food chain, potentially placing humans at risk too.

Now a team at the Kyoto Institute of Technology led by scientist Shosuke Yoshida, writing in the journal Science, has found a strain of microbe naturally endowed with the necessary metabolic knife and fork to enable it to eat PET.

The Japanese team found the microbe, which is called Ideonella sakaiensis, among 250 samples collected from PET-contaminated sites.

These include swabs of sediments, soils, wastewater and even sludge found at a PET-recycling plant. In a simple series of tests they screen through their samples for any microbes that appeared to be able to degrade thin films of PET.

One of the specimens tested appeared to be breaking down PET at the rate of 0.13mg per square centimetre per day, but under the microscope it appeared to be a consortium of different microbes, including bacteria and fungi.

To find out which of the bugs were doing the digestion, the team separated the cosortium into individual microbial groups and tested each individually.

The Ideonella species, which the team have dubbed Ideonella sakaiensis 201-F6, emerged as possessing the PET-degrading chemistry.

The researchers purified and identified the chemical pathway responsible by looking at which genes the bacteria turned on when they grew on PET compared with being fed on sugars. Two enzymes, they discovered, were responsible and which they are calling "PETase".

How the bacteria came by these genes is unknown, because they bear no resemblance to other genes in the same bacterial family.

Instead the scientists suspect that the process of "lateral gene transfer", where bacteria grab random genes they can use from the environment, is probably responsible.

These genes would have enabled the bacteria to access a novel source of carbon - PET - and the advantage would have led to them becoming fixed in the population.

Optimising these agents might be one way to clean up the millions of tonnes of plastic waste currently lying around the planet...


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