By Ross Pomeroy
Drop a few waxworms of the species Galleria mellonella into a plastic bag, and you may find yourself without a bag. New research published to the journal Current Biology shows that these waxworms, the caterpillar larvae of honeycomb moths, are capable of digesting and biodegrading polyethylene, the most common form of plastic.
You know polyethylene well. Eighty million metric tons of the stuff are produced each year, most commonly in the form of bags, films, and bottles. You probably also know that polyethylene is not readily biodegradable. The special treatments required to recycle the plastic are very expensive, so the overwhelming majority of waste ends up in landfills.
Enter insects. In 2015, researchers demonstrated that mealworms could eat and digest polystyrene, the plastic synonymous with plates, cups, and take-out boxes, with the aid of their gut bacteria. A year before, that same group showed that bacteria inside the guts of waxworms of the Indian mealmoth can degrade polyethylene.
It was this finding that set the stage for the present study. Scientists Federica Bertocchini, Paolo Bombelli, and Chris Howe noticed that plastic bags containing waxworms rapidly became riddled with holes, so they decided to "feed" the worms in a more controlled fashion. In numerous settings, they left the caterpillars alone with various plastic films and observed what happened. Invariably, the plastic films would end up pockmarked with holes. In the most striking example, the team left one hundred waxworms with a plastic bag. After twelve hours, the hungry critters had devoured 92 milligrams of it.
To confirm that the plastic was actually getting digested and not merely chewed up and excreted, the researchers smeared mashed-up waxworms (euphemistically dubbed "homogenate") on polyethylene films. Fourteen hours later, the films had lost an average of 13% of their mass.
So how are these caterpillars able to eat plastic?
"The answer may lie in the ecology of the waxworm itself," the researchers hypothesize. "They feed on beeswax... Beeswax is composed of a highly diverse mixture of lipid compounds, including alkanes, alkenes, fatty acids, and esters."
Overall, this hodgepodge of chemicals is fundamentally similar to plastic, the researchers say. Both beeswax and polyethylene are primarily built with the same hydrocarbon bond, and it seems the bacteria populating waxworm intestines are capable of breaking it down.
The researchers are working on a way to commercialize the discovery now. Their aim is to create a viable way to get rid of plastic waste. Such a strategy is likely years away, but it can't come soon enough!
Source: Federica Bertocchini, Paolo Bombelli, and Chris Howe. Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella. Current Biology 27, R1–R3. http://dx.doi.org/10.1016/j.cub.2017.02.060