A Solution for Rubbish?
(October 10th, 2017) Earlier this year, scientists claimed that a caterpillar is able to digest plastic. But, as another team points out, their analysis is not conclusive.
What if there was an easy solution to get rid of all our rubbish? A team from the University of Cantabria, Spain and the University of Cambridge, UK, may have discovered a way to achieve just that with caterpillars.
The idea to test these animals came from an unlikely source: beekeeping in the North of Spain, where scientist/amateur bee keeper Frederica Bertocchini keeps her beehives. Annoyingly, over the years, they kept being infested with Galleria mellonella caterpillars. Also known as wax moths, these small creatures can actually eat through the wax and cause severe damage to the beehives. Seeing that plastic bags used to store her tools were repeatedly covered in holes sparked her curiosity and Bertocchini decided to contact old friend, biochemist Paolo Bombelli, to investigate this mystery.
Together, they discovered that it’s not only wax that G. mellonella caterpillars can eat but it appears they can also munch on plastic. In fact, FITR analysis revealed the presence of extra peaks, which the researchers attributed to ethylene glycol, the product of polyethylene degradation (one of the main components in plastic). “The most exciting result is the bio-degradation itself,” says Bombelli. “Indeed, the extra peaks from the FITR analysis are pointing in the direction of some degree of chemical transformation.”
The exact mechanism behind this degradation is still unknown but as Bombelli notes, there is “some similarity between the structure of bee wax, a natural polymer which G. mellonella is constantly exposed to, and the structure of polyethylene”.
Given our worldwide issues with rubbish, it’s tempting to see this as a perfect solution to our landfill problem. It may, however, be premature to jump to this conclusion. According to Bombelli, the way forward may not necessarily involve large numbers of caterpillars but might, for example, use bacteria modified to produce the enzyme(s) involved. The duo is planning to continue this research in the future, hoping that it “will turn into a successful project soon”.
This work has met some criticism from a team of chemists from the University of Mainz, Germany. Their issue is certainly not the idea that these caterpillars can eat plastic but the assumption that the FITR peaks are attributed to ethylene glycol. “I was a bit surprised by the interpretation, because I thought that it looked like a protein,” explains Till Opatz. “The peak they used is a non-specific peak that could be anything, O-H, N-H. It’s not possible based in this absorption to pinpoint the compound that was present.”
After a quick experiment with pork meat and egg yolk, Opatz is more inclined to believe the extra peaks are lipids and proteins. At the moment, “we can neither prove that the caterpillars are digesting polyethylene nor can we disprove it”, says the researcher. “Further experiments are absolutely needed to check whether this is really degradation of polyethylene. All we can say is that the experiments that were done in the paper are not enough to make the statement that caterpillars digest plastic.”
Bombelli and Bertocchini were fast to reply, saying that the peaks to correctly identify ethylene glycol may be small but they are present and worthy of further investigation. After Opatz’s suggestion, they agree that one sure way to find out whether G. mellonella caterpillars can digest plastic is to use 13C-labelled polyethylene and follow 13C, until it’s released as CO2 or incorporated into the caterpillar’s body.
Despite the disagreement, both teams can see the potential applications. “If you find an organism that is able to digest polyethylene it would be huge, because we would produce these organisms in a large quantity or even just take the enzyme out of the organism and analyse it,” says Opatz. “Polyethylene is really hard to break. If an enzyme can do this, it would be very interesting to find out how it does it. Maybe we could use the same enzyme to convert paraffin-derived products that can be produced from petroleum into something very valuable.”