Federica Bertocchini, developmental biologist of the Institute of Biomedicine and Biotechnology of Cantabria, Spain has reported a promising discovery in collaboration with the University of Cambridge. Thanks to her hobby of beekeeping, this amateur beekeeper, has accidentally found that wax worms that infested one of her honeybee combs have the capacity to degrade plastic. The research reports fast biodegradation of Polyethylene (PE) by larvae of the wax moth Galleria mellonella and the production of ethylene glycol.
Plastics are synthetic polymers derived from fossil oil, that are mostly resistant to biodegradation. For over 50 years, global production of plastic has sustained to increase. This rise in manufacturing has led to plastic pollution, accumulating plastic products in the environment that adversely affects wildlife, wildlife habitat, and humans. Approximately 92% of the total plastic produced consists of Polyethylene (PE) and polypropylene (PP), where PE is mainly employed in packing with ~40% of total demand for plastic products. PE contains a linear backbone of carbon atoms that is resistant to degradation.
Highlights of plastic production from Worldwatch Institute analysis (2015):
• About 4 percent of the petroleum consumed worldwide each year is used to make plastic, and another 4 percent is used to power plastic manufacturing processes.
• In Europe, 26 percent, or 6.6 million tons, of the post-consumer plastic produced in 2012 was recycled, while 36 percent was incinerated for energy generation. The remaining 38 percent of post-consumer plastics in Europe went to landfills.
• In the United States, only 9 percent of post-consumer plastic (2.8 million tons) was recycled in 2012. The remaining 32 million tons was discarded.
• Asia uses just 20 kilograms per person, but this figure is expected to grow rapidly as economies in the region expand.
The study was published in current biology, the research explains fast biodegradation of PE by the wax worm, the caterpillar larva of the wax moth Galleria mellonella belonging to the family of snout moth (Pyralidae) of Lepidoptera. When the authors reared 100 wax worms directly on a PE film holes started to appear within 40 minutes. To be sure that the mechanical action of the masticatory system was not the sole reason for the observed degradation PE the researchers conducted experiments with worm homogenate. The wax worms were homogenized and the worm homogenate was applied on the PE film and left for 14 hours. After analyzing the treated samples with that of controls (untreated samples) they confirmed that there was a loss of 13% PE after treatment.
The reason and the mechanism:
The ecology (the study of interactions among organisms and their environment) of the wax worm itself answers the question how this worm is able to break a chemical bond which is not susceptible to biodegradation. The wax worm lives in the honeycomb and feeds on the beeswax. The greater wax moth lays its eggs inside the beehive, where the caterpillar larvae or waxworms grows to their pupa stage eating the beeswax inside the bee nests.
Beeswax is a mixture of various lipid compounds like alkanes, alkenes, fatty acids, and esters. The most common bond found in hydrocarbons is CH2–CH2 and it is also present in PE. The C-C single bond of these lipid compounds seems to be one of the targets of digestion. But the molecular details of wax biodegradation are yet to be investigated. The authors reported that the presence of holes on PE plastic bags when they are in direct contact with the wax worms, and the FTIR examination of the degraded PE indicated the chemical breakdown of the PE, which also included the breakage of C–C bonds.
Is wax worn the only organism that can biodegrade plastic:
Perilously, before wax worm came into the picture several other researchers have made few attempts to find an organism that can degrade plastic. When optimal conditions were slow (weeks/months) PE biodegradation has been observed. For example, modest degradation of PE has been observed with nitric acid treatment and incubation of 3 months in a liquid culture of a fungus Penicillium simplicissimum. A bacteria Nocardia asteroides has also been tested which showed slow PE degradation after 4 to 7 months. But this is the first report of efficient degradation of PE reported till date.
The authors of the study are not clear whether the hydrocarbon-digestion by G. mellonella is driven by the organism itself or from the enzymatic activities of its gut microbiome. Further study is required to determine if other related species of the wax worm have the capacity for PE degradation, and also the analysis of its molecular basis including the detailed nature of the products.
Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella. Bombelli P, Howe CJ, Bertocchini F. Curr Biol. 2017 Apr 24; 27(8):R292-R293. [PMID:28441558]