A chance discovery made by a scientist and amateur beekeeper has led to a potentially game-changing discovery in the biodegrading of polyethylene, a plastic used in shopping bags that clog up landfill sites and pollute our oceans.
Federica Bertocchini, from the Spanish National Research Council (CSIC), removed a batch of wax worms, the larvae of the common insect Galleria mellonella (greater wax moth) from honeycombs in her hives. Such larvae are a scourge of beehives across Europe, laying eggs that hatch and grow on beeswax.
Bertocchini placed the worms in a typical plastic shopping bag. Soon she discovered the bag riddled with holes.
Alongside University of Cambridge biochemists colleagues Paolo Bombelli and Christopher Howe, Bertocchini conducted a timed experiment in which 100 worms were exposed to a plastic bag.
Within 40 minutes holes began to appear, and after 12 hours a reduction in plastic mass of 92 milligrams from the bag had appeared. Further studies will be needed to discriminate the mechanical from the chemical degradation, but the rate was overall faster than that seen in an experiment reported last year by scientists in Japan who used a species of bacteria to degrade polyethylene terephthalate (PET), a plastic used in water bottles.
“Our discovery showed that the rate of degradation is faster,” Bombelli said. “The question we still need to address is ‘Are we really dealing with some sort of enzyme created by the larvae?’ or perhaps there are bacteria—perhaps different bacteria from what have been characterized before. All these questions remain open and we need to work on this.”
Researchers used spectroscopic analysis to show the characteristic spectrum of PE was altered. This indicated that the structure of PE bonds in the plastic were breaking, transforming the polymer of polyethylene into smaller products.
To prove that it wasn’t merely the chewing mechanism of the caterpillars degrading the plastic, researchers mashed up some of the worms and smeared them on polyethylene bags. This produced similar results.
“First of all there are some peaks in the infrared spectroscopy that you cannot generate only with mechanical action [chewing],” said Bombelli. “Of course, someone could argue that not necessarily all these peaks can be explained by degradation of polyethylene, but then also you can notice that the surface, the roughness of the surface, was changed. This means that something is actually attacking the surface on the microscopic level.”
The scientists believe that digesting beeswax and polyethylene involves breaking down similar types of chemical bonds, which they hope to prove with further analysis.
Galleria mellonella is bred commercially for fishing bait, and Bombelli says its larvae would not be necessary to create a large-scale biotechnological solution for managing polyethylene waste.
“Any discovery in this field could really contribute to create technological solutions for minimizing the plastic waste.....Probably we are not going to create a facility with billions of larvae. Ideally after discovering the enzymes, perhaps we can express these enzymes in vector like E.coli of yeast and then use these in a more biotechnological way.”
Polyethylene is one of the most commonly used plastics globally. It accounts for around 40 percent of total demand for plastic products across Europe, a continent where up to 38 percent of plastic is discarded in landfills, where it is thought it will take up to 400 years to degrade.
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