Biodegradation Of Polystyrene And Polyethlene By The Greater Wax Moth Larvae And The Effect On Their Gut Microbiome

“White pollution” has adversely affected the ecological environment and human health and has become one of the most concerned environmental issues in the world.In2017,the global plastic production has been raised to 350 million tons.So far,traditional non-biological treatment methods such as landfilling and incineration are effective in plastics degradation,and such methods will cause secondary pollution to the environment.Biological degradation of plastics are more environmentally friendly but still requires further research.In this study,the larvae of greater wax moth(Galleria mellonella)was used as the experimental object.This experiment not only confirmed the phenomenon that the larvae of the greater wax moth is capable of chewing the plastic foam,but also proved that the larvae has the ability to degrade plastics.Besides,the degradation rate and products of plastic by the larvae were explored,and the effect of adding beeswax or wheat bran as supplement nutrients were also discussed.In addition,through the analysis of the intestinal community structure of the larvae,functional strains that may be involved in the plastic degradation process were inferred.The main results of this paper are as follow:(1)The experiment explored and confirmed the phenomenon that the larvae are capable of chewing and ingest plastic foam.Larvae prefer polyethylene better than polystyrene.When nutrients such as wheat bran or beeswax are added as supplementary carbon sources,the survival rate of larvae was significantly improved,and the plastics consumption of larvae was decreased.Therefore,the tendency to reduce the rate of eating plastics occurred after the addition of wheat bran or beeswax.(2)Thermogravimetric analysis(TGA),fourier transform infrared spectroscopy(FTIR)and gel permeation chromatography(GPC)analysis demonstrated that the larvae of the greater wax moth is capable of degrading polystyrene and polyethylene foam.After the larvae chew and ingested the plastic,the depolymerization and chain scission of the long-chain polymer leads to a decrease in the molecular weight of the substance.Infrared spectroscopy confirms the formation of a new oxygen-containingfunctional group,thus confirming that the plastic is degraded after passing through the larval intestinal tract.(3)Finally,the larvae of the greater wax moth were dissected,and the DNA of the intestinal bacteria was extracted for community analysis.Based on the microbial community analysis,we explored the principle of intestinal flora for plastic degradation and searched for the plastic-degrading strains.16 S rRNA gene sequencing was performed on the Illumina HiSeq sequencing platform.The results showed that strains in the intestinal tract of the larvae can participate in the process of degrading polyethylene and polystyrene plastics.Larvae that feed on plastics and nutrients such as beeswax and wheat bran showed obvious differences in the intestinal microbiome.The results showed that the dominant species that feed on polystyrene were Enterococcus,Geobacillus and Pseudomonas.It may be involved in the process of degrading polystyrene plastics.The dominant gut species of larvae fed with polyethylene was Serratia;Enterococcus is a common genus of intestinal tract,which is commonly found in the intestines of larvae under various feeding methods.In summary,this research has created a disruptive technology,a new approach and direction,and provided important research objects.Experiments can confirm the existence of larvae capable of degrading macromolecules plastics.The larvae gut is a highly efficient bioreactor for degrading plastics.It can utilize the potential plastic degrading bacteria in the insect gut to construct a plastic degradation system so as to achieve efficient degradation of plastics,and also provides a new idea for solving the worldwide problem of biodegradation of "white pollution".