New ‘Living Plastic’ Self-Destructs Once It’s Thrown Away
Scientists have created a ‘living plastic’ that self-destructs when the material begins to erode.
In the composting process, the novel product breaks down within a month, compared with more traditional versions that take up to 55 days to decompose under the same conditions.
The hopeful technology was inspired by the power of plastic-munching proteins, which are naturally produced by a species of bacteria discovered in 2016 at a recycling facility in Japan.
In the years since scientists have found several other species of bacteria that have evolved the enzymes to eat plastic, and these natural proteins have inspired synthetic versions that are even hungrier for our waste.
Researchers at the Chinese Academy of Sciences (CAS), led by synthetic biologist Chenwang Tang, have now figured out how to bake bacterial spores that secrete these enzymes into the very structure of polycaprolactone (PCL) plastic.
That way, when the plastic begins to degrade, these newly freed enzymes can finish off the task.
Being large, complex proteins, enzymes are often unstable or even fragile. So the researchers engineered the gene for a lipase enzyme from the bacterium Burkholderia cepacia (BC) into the DNA of another microbe called Bacillus subtilis, which in spore form is resistant to high temperatures and pressures.
As the surface of the plastic erodes, the liberated spores begin to germinate. The growing B. subtilis then expresses its copy of BC-lipase, which sets to work almost completely degrading the PCL molecules.
When a second lipase produced by the yeast Candida antarctica was used to speed up the process, the plastic degraded within a week, Tang and his colleagues at CAS found. By contrast, traditional PCL plastics treated the same way still persist after three weeks.
The temperatures and pressures required to create PCL aren’t as extreme as the conditions required for other plastics. To test whether the spores could survive the processing needed to create other plastics, researchers at CAS engineered the bacteria to express fluorescent markers.
Plastic products tested include PBS (polybutylene succinate), PBAT (polybutylene adipate-co-terephthalate), PLA (polylactic acid), PHA (polyhydroxyalkanoates), and even PET (polyethylene terephthalate) plastic, which requires temperatures as high as 300 oC. When physically degraded or boiled, the spore-embedded plastics began to glow.
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