Transcriptomic Response of Superworm in Facilitating Polyethylene Biodegradation

Plastics are a serious cause of environmental pollution, and microplastics pose a threat to human health. To solve this problem, the plastic-degrading mechanism of insect larvae is being investigated. The aim of this study was to examine the metabolic pathways involved in polyethylene metabolism, the interaction between the host and microorganisms, and the role of superworms in promoting plastic degradation in polyethylene-fed superworms. Through host transcriptomic analysis, we identified 429 up-regulated and 777 down-regulated genes and analyzed their functions using the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology databases. We found that insects promote the degradation of polyethylene through two main mechanisms. First, polyethylene metabolites activate the lipid metabolism pathway in insects, promoting the synthesis of carboxylic ester hydrolases and accelerating polyethylene degradation. Second, insect larvae generate reactive oxygen species (ROS) which are critical for insect immune responses and for the initial oxidation of polyethylene. In metagenomic analysis, bacterial species, such as Citrobacter sp. and Raoultella sp., which are known to be involved in the degradation of polyethylene and its metabolites, were more abundant in the guts of insects that consumed polyethylene. In addition, increases in the concentration of peroxide in the gut and the activity of esterase (lipase) acting on lipophilic substrates were observed. Furthermore, we suggest that xenobiotic metabolism is critical for polyethylene metabolism in superworm guts. In particular, enzymes involved in xenobiotic metabolism phase 2, such as glutathione S-transferase and uridine diphosphate glycosyltransferase, convert lipophilic plastic degradation intermediates into water-soluble forms and promote polyethylene degradation.