Eisenia andrei and Tenebrio molitor Divergently Restructure the Bacteriome and Mycobiome of Sewage Sludge with Contrasting Biosafety Consequences

The use of invertebrates for sewage sludge bioconversion offers a sustainable strategy for waste valorization, yet species-specific effects on microbial communities and biosafety remain unclear. Here, we compared the impacts of the earthworm Eisenia andrei (Ea) and the mealworm Tenebrio molitor (Tm) on the bacteriomes and mycobiomes of sewage sludge (ss) using 16S rRNA and ITS amplicon sequencing. Gut passage in both Ea and Tm markedly altered bacterial and fungal composition relative to ss, but produced distinct community profiles with differential shifts across multiple taxa. Both invertebrates reduced bacterial richness by ~40%, while fungal responses diverged: Ea largely preserved mycobiome richness despite reduced evenness, whereas Tm caused a near-complete collapse (~83% Amplicon Sequence Variant loss). Beta diversity analyses revealed clear, non-overlapping separation among ss, Ea, and Tm for both microbial domains. Tm frass showed strong enrichment of clinically relevant bacterial pathogens, while Ea casts exhibited no such enrichment. For fungi, Ea reshaped pathogen composition, whereas Tm largely eliminated fungal pathogens through broad community collapse. Both treatments reduced predicted antibiotic resistance gene abundance, but functional profiles differed, with Ea showing greater functional stability. These findings demonstrate that microbiome restructuring during bioconversion is species-dependent, with contrasting ecological and biosafety implications for downstream environmental use.