Mechanisms and Perspectives of Microplastic Biodegradation by Insects and Their Associated Microorganisms

Plastic pollution, particularly the widespread presence of microplastics, has emerged as a global environmental threat. Conventional plastics are highly resistant to degradation and can persist in ecosystems for decades, posing a serious long-term risk to wildlife, habitats, and human health. Increasing evidence suggests that insects and their gut microbiota may play a significant role in the degradation of these plastics. This review examines the mechanisms by which insects and their associated microorganisms contribute to microplastic biodegradation. Plastivorous insect larvae such as Spodoptera frugiperda, Galleria mellonella, Tenebrio molitor and Zophobas atratus have demonstrated the ability to ingest and partially degrade diverse polymers. The initial mechanical breakdown caused by insect mandibles increases the surface area, which allows gut microbes to colonize the material. Once these microbes are established, they form biofilms that help with adhesion, create localized redox environments, and concentrate degradative enzymes at the polymer interface. The enzymatic machinery of insect-associated microbes plays a crucial role in breaking down polymers. Oxidative enzymes, including DyP-type peroxidases, multicopper oxidases, alkane monooxygenases, and laccases, initiate the oxidation of polymers, while hydrolases and esterases further break down the resulting fragments. Co-metabolic processes and microbial consortia improve degradation efficiency by primary degraders by producing oxidized intermediates, which are then consumed and mineralized by secondary fermenters. Despite significant progress, the complete biochemical pathways of microplastic mineralization remain unclear. Degradation rates are slow, and scalability challenges hinder practical applications, with incomplete mineralization in insect biodegradation potentially causing secondary microplastics. Understanding these mechanisms will lay the groundwork for developing insect-microbe systems as potential biotechnological solutions to mitigate plastic pollution in terrestrial environments.