Gut microbiome facilitates black soldier fly-mediated bioconversion under zinc stress.

The microbiome plays an important role in manure transformation in the black soldier fly (BSF), yet the mechanisms by which it promotes host tolerance to zinc stress remain poorly understood. Here, we show that the gut microbiome promotes larval growth using a controlled zinc-supplemented wheat bran model. High dietary zinc significantly impairs BSF larval growth and development and results in a pronounced reduction in gut length. Using germ-free and gnotobiotic BSF larvae, we find that zinc-induced growth arrest is significantly alleviated by inoculation with Pediococcus acidilactici strain AH1, Bacillus cereus strain AH3, Klebsiella pneumoniae strain AH4, or a consortium of three isolates. Metatranscriptomic analysis reveals that key microbial pathways, including peptidoglycan synthesis and degradation, microbial defense systems, biofilm formation, and zinc metabolism, are upregulated under zinc stress. Moreover, the microbiome facilitate dietary zinc fraction redistribution and reduced host zinc accumulation. Microbial reconstitution further activates host antioxidant responses and mitigates zinc-induced oxidative damage. Together, these findings highlight the critical role of the microbiome in zinc tolerance of BSF larvae, providing insights for future efforts to explore microbiome-assisted optimization of BSF-mediated bioconversion under zinc stress conditions.