Microplastic–metal–microbiota interactions in the flesh fly Boettcherisca peregrina larvae reared on contaminated livestock manure

Microplastics in livestock manure pose a growing environmental concern, which could possibly enhance the bioavailability of heavy metals to flesh fly, such as the Boettcherisca peregrina, a candidate biological agent for manure valorization. In this study, the impact of polystyrene microplastics (PS MPs, 0-0.1 mg/g) on larval growth, heavy metal accumulation and gut microbiota in B. peregrina that were reared on bovine liver, swine manure, and chicken manure were investigated. The PS MPs can be easily ingested by the larvae, but hardly affect the larval weight and growth. Conversely, the PS MPs can significantly shorten adult lifespan (by 25.6 %) with rearing by chicken manure. The PS MPs significantly promoted the accumulation of As, Cr, Cu, and Fe in 3rd instar larvae, exhibiting a concentration-dependent effects. Furthermore, PS MPs primarily localized in the epidermis of 3rd instar larvae. The PS MPs can also localize in gut, resulting in diet dependent associations with heavy metal distributions. Exposure to PS MPs substantially restructured microbial associations, particularly by suppressing genera such as Lactobacillus, Clostridium, and Enterococcus that are involved in heavy metal detoxification. Overall, our findings reveal a tripartite interaction among MPs, heavy metals, and host gut microbiota, underscoring the urgency to integrate MPs associated risks into waste-to-protein bioconversion frameworks.