Mutant Enzyme that Eats Plastic Bottles

Scientists have created a mutant enzyme that breaks down plastic drinks bottles – by accident as posted in the Guardian recently on April 16th! The breakthrough could help solve the global plastic pollution crisis by enabling for the first time the full recycling of bottles.

The new research was spurred by the discovery in 2016 of the first bacterium that had naturally evolved to eat plastic, at a waste dump in Japan. Scientists have now revealed the detailed structure of the crucial enzyme produced by the bug.

The international team then tweaked the enzyme to see how it had evolved, but tests showed they had inadvertently made the molecule even better at breaking down the PET (polyethylene terephthalate) plastic used for soft drink bottles. “What actually turned out was we improved the enzyme, which was a bit of a shock,” said Prof John McGeehan, at the University of Portsmouth, UK, who led the research. “It’s great and a real finding.”

The mutant enzyme takes a few days to start breaking down the plastic – far faster than the centuries it takes in the oceans. But the researchers are optimistic this can be speeded up even further and become a viable large-scale process.

“What we are hoping to do is use this enzyme to turn this plastic back into its original components, so we can literally recycle it back to plastic,” said McGeehan. “It means we won’t need to dig up any more oil and, fundamentally, it should reduce the amount of plastic in the environment.”

About 1m plastic bottles are sold each minute around the globe and, with just 14% recycled, many end up in the oceans where they have polluted even the remotest parts, harming marine life and potentially people who eat seafood. “It is incredibly resistant to degradation. Some of those images are horrific,” said McGeehan. “It is one of these wonder materials that has been made a little bit too well.”

Original link here: https://www.theguardian.com/environment/2018/apr/16/scientists-accidentally-create-mutant-enzyme-that-eats-plastic-bottles

Why is Plastic Non-biodegradable?

Most plastic is manufactured from petroleum the end product of a few million years of natural decay of once-living organisms. Petroleum’s main components come from lipids that were first assembled long ago in those organisms’ cells. So the question is, if petroleum-derived plastic comes from biomaterial, why doesn’t it biodegrade?

A crucial manufacturing step turns petroleum into a material unrecognized by the organisms that normally break organic matter down.

Most plastics are derived from propylene, a simple chemical component of petroleum. When heated up in the presence of a catalyst, individual chemical units monomers of propylene link together by forming extremely strong carbon-carbon bonds with each other. This results in polymers long chains of monomers called polypropylene.

“Nature doesn’t make things like that,” said Kenneth Peters, an organic geochemist at Stanford University, “so organisms have never seen that before.”

The organisms that decompose organic matter the ones that start turning your apple brown the instant you cut it open “have evolved over billions of years to attack certain types of bonds that are common in nature,” Peters told Life’s Little Mysteries.

“For example, they can very quickly break down polysaccharides to get sugar. They can chew up wood. But they see a polypropylene with all its carbon-carbon bonds, and they don’t normally break something like that down so there aren’t metabolic pathways to do it,” he said.

But if all you have to do to make propylene subunits turn into polypropylene is heat them up, why doesn’t nature ever build polypropylene molecules?

According to Peters, it’s because the carbon-carbon bonds in polypropylene require too much energy to make, so nature chooses other alternatives for holding together large molecules. “It’s easier for organisms to synthesize peptide bonds than carbon-carbon bonds,” he said. Peptide bonds, which link carbon to nitrogen, are found in proteins and many other organic molecules.

Environmentalists might wonder why plastic manufacturers don’t use peptide bonds to build polymers rather than carbon-carbon bonds, so that they’ll biodegrade rather than lasting forever in a landfill . Unfortunately, while peptide bonds would produce plastics that biodegrade, they would also have a very short shelf life. “It’s an issue of ‘you can’t have your cake and eat it too,'” said Jim Coleman, chief scientist at the US Geological Survey Energy Resources Program. “When you buy a plastic jar of mayonnaise, you want [the jar] to last a few months.” You don’t want it to start decomposing before you’ve finished the mayo inside.

For the original article visit livescience.com!

[Photo Credit: Antonio Oquias | Dreamstime]