Black soldier fly bioconversion improves agronomic value but sustains resistome risks in silver-bearing sewage sludge...

Agricultural reuse of sewage sludge can improve crop production but may also introduce metals and antibiotic resistance genes (ARGs) into soil-plant systems. We evaluated sludge-derived composts, with and without black soldier fly (BSF) bioconversion, in a red amaranth pot experiment under exposure to silver nanoparticles (Ag-NPs) and silver sulfide nanoparticles (Ag₂S-NPs). During composting, BSF was associated with greater dissolved organic matter humification, reduced extractable Ag and co-existing metal concentrations, while Ag exposure selectively reshaped compost microbiota and the BSF gut resistome. However, BSF bioconversion remained the main driver of microbial community reassembly, whereas Ag exposure mainly promoted host turnover and mobile genetic element enrichment rather than broad ARG amplification. After soil application, compost significantly enhanced red amaranth growth. Total biomass increased from 1.3 g pot^-1 in the unfertilized control to 3.8 g pot^-1 with BSF-derived compost and 5.1-5.2 g pot^-1 with BSF-derived Ag₂S-NP composts, accompanied by higher shoot N and P concentrations. However, shoot Ag and selected co-existing metals also increased, indicating an agronomic benefit-risk trade-off. Metagenomic analyses showed that compost application reshaped the rhizosphere resistome mainly through host filtering, with ARG dissemination potential linked to the co-localization of ARGs, metal resistance genes, and mobile genetic elements in a limited number of enriched hosts. Plant growth was driven mainly by fertilization and nutrient status, whereas ARG abundance was associated primarily with metals, metal resistance genes, and gene mobility. These findings support BSF-assisted sludge recycling as a promising but risk-aware strategy for agricultural reuse.