Plastics are synthetic polymers derived from fossil oil and mostly resistant to biodegradation. Polyethylene (PE) and polypropylene (PP) represent ~92% of total plastic production. PE is largely used in packaging –– representing ~40% of total demand for plastic products, with over a trillion plastic bags used every year. Plastic production has increased exponentially in the past 50 years. In the 27 EU countries plus Norway and Switzerland, up to 38% of plastic is discarded in landfills, with the rest used for recycling (26%) and energy recovery (36%) by means of combustion, carrying a heavy environmental impact.
Therefore, new solutions for plastic degradation are urgently needed. Authors [see attached publication] report the fast biodegradation of PE by larvae of the wax moth Galleria mellonella, producing ethylene glycol. The caterpillar larva of the wax moth, Galleria mellonella, is a member of the snout moth (Pyralidae) family of Lepidoptera. When a PE film was left in direct contact with wax worms, holes started to appear after 40 minutes, with an estimated 2.2 ± 1.2 holes per worm per hour. The impact of 100 wax worms in contact with a commercial PE shopping bag for 12 hours caused a mass loss of 92 mg.
Why might the wax worm degrade a chemical bond that is generall resistant to biodegradation? The answer probably lies in the ecology of the wax worm itself. They feed on beeswax, and their natural niche is the honeycomb; the moth lays its eggs inside the beehive, where the worms grow to their pupa stage, eating beeswax. Beeswax comprises a highly diverse mixture of lipid compounds, including alkanes, alkenes, fatty acids and esters. The most frequent hydrocarbon bond in beeswax is the CH2–CH2, which exists in the PE molecule. It seems likely that the C–C single bond of aliphatic compounds is one of the targets of digestion.
It is not yet known whether the hydrocarbon-digesting activity of G. mellonella originates from the organism itself, or from enzymatic activities of its intestinal flora –– which happens to be the case for PE digestion by Plodia interpunctella. Further investigation is also required to determine if related species have the capacity for PE degradation, and to analyze its molecular basis including the detailed nature of the products. Nevertheless, these intriguing findings have potential for significant biotechnological applications.
Curr Biol 2o17; 27: R292–R293