They found the first ones in Japan. Hidden in the soil of a plastic recycling plant, the researchers unearthed a microbe that had evolved to eat the soda bottles that dominated their habitat, after you and I threw them.
That discovery was announced in 2016, and scientists have now been better. By examining how the Japanese virus breaks down plastic, they accidentally created a mutant enzyme that outperforms natural bacteria, and other adjustments could offer a vital solution to the colossal problem of plastics.
"Chance often plays an important role in fundamental scientific research and our discovery here is no exception," says structural biologist John McGeehan of the University of Portsmouth in the United Kingdom.
"This unforeseen discovery suggests that there is room to further improve these enzymes, approaching a recycling solution for the growing mountain of discarded plastics."
McGeehan's team, including researchers at the National Renewable Energy Laboratory (NREL) of the US Department of Energy . UU., They came across their mutant modification while investigating the crystalline structure of PETase: the enzyme that helps the Japanese microbe, Ideonella sakaiensis decompose PET plastics (also known as polyethylene terephthalate).
PET was patented in the 1940s, and while it seems that it was a long time ago, in evolutionary terms it is quite recent. The point is, while I. sakaiensis can actually eat plastic, only recently has he had the opportunity to learn this trick, which means he can not eat very fast.
That's a problem, given the large amount of plastic pollution on the planet, with billions of tons of discarded waste accumulating in landfills and dumped into our oceans, where it even threatens to displace the fish, seriously.
Not that PETase is a shrimp, since PET itself takes centuries to decompose naturally, and the enzyme allows the bacteria to shorten that in a matter of days.
"After only 96 hours it can be clearly seen through electron microscopy that PETase degrades PET", says the NREL structural biologist Bryon Donohoe.  "And this test uses real examples of what is found in oceans and landfills."
To examine the efficiency of PETase at the molecular level, the team used X-rays to generate a model Ultra high resolution 3D of the enzyme, revealing an unprecedented view of PETas The active site of e that allows you to grab and break your PET target, and also, by chance, how that mechanism can be improved.
"Being able to see the internal workings of this biological catalyst gave us the blueprints to design ar faster and more efficient enzyme, "says McGeehan.
Hypothesizing that the PETase enzyme must have evolved in the presence of PET to discover how to degrade the plastic, the researchers mutated the active site of PETase, to see if they could bring it closer to another enzyme, called cutinase.
Although they did not expect it, this adjustment ended up showing that the enzyme could be further optimized in terms of plastic decomposition.
"Surprisingly, we found that the PETase mutant exceeds the wild type PETase in degradation of PET, "says materials scientist NREL Nic Rorrer.
"Understanding how PET is bound in the PETasa catalytic site using computational The tools helped to clarify the reasons for this improved performance, taking into account these results, it is clear that there is still a significant potential to further improve its activity "
While the PETase mutant is up to now only 20 percent more efficient in breaks In addition to the natural enzyme, the team says the important thing is that we now know that these enzymes can be optimized and increased.
That means that future engineering versions should work even better to chew plastic, and they could help us also recycle other types of materials.
For example, the modified PETase can also decompose a PET substitute called FEF (polyethylene furandicarboxylate), which the natural PETase can not process.
It will take time before these innovations can be seized to break through the billions of tons of plastic we have already accumulated, but now that we have a proof of concept, we can use science to help nature break down an unnatural material that simply will not disappear fast enough otherwise.
"What we have learned is that PETase is not yet fully optimized to degrade PET," explains NREL biotechnologist Gregg Beckham.
"And now that we've proven this, it's time to apply the tools of protein engineering and evolution to keep improving."
The results are reported in Proceedings of the National Academy of Sciences ] (link at the time of writing).