Long-term effect of plastic feeding on growth and transcriptomic response of mealworms (Tenebrio molitor L.)

Plastic waste has been considered one of the serious global environmental problems for decades. Despite the high recalcitrance of many synthetic plastics, the biodegradation of polyethylene (PE) and polystyrene (PS) by some insect larvae has been reported, though the mechanism of degradation has remained largely unknown. We investigated the effects of plastics on the growth of mealworm (larvae of Tenebrio molitor) and its role in PS and PE degradation. Among the plastics studied, mealworm was capable of ingesting high impact polystyrene (HIPS), expanded polystyrene (EPS) and low-density polyethylene (LDPE), but not linear low-density polyethylene (LLDPE) and polypropylene (PP). Plastic consumption, which contributed very little to growth of larvae, depended negatively on plastic crystallinity. Notably, mealworm failed to grow by feeding on plastics alone. Transcriptome analysis and KEGG mapping revealed that mealworm was acting as the downstream decomposer in plastic depolymerization, and the pathway of fatty acid degradation played important roles in the digestion of plastic degradation intermediates produced by gut bacteria. In addition, degradation of PS and PE was achieved by diffusion of extracellular depolymerases, reacting on the distal backbone and producing shorter linear chains containing less than 16 C instead of the branched chains. The results demonstrated the role of mealworm in plastic degradation and revealed more research efforts were needed on plastic degradation using mealworm.