Synergistic reshaping of nitrogen flow by black soldier fly and gut ammonia-assimilating bacteria: Green transformation from nitrogenous waste to insect protein

Soy curd residue (SCR), a high-organic-nitrogen waste, faces challenges in efficient valorization due to its imbalanced carbon-to-nitrogen (C/N) ratio leading to large amount nitrogen loss and low bioconversion efficient which posed dual challenges of resource wastage alongside environmental pollution and climate risks. Black Soldier Fly larvae (BSFL) with its gut microbiota have been proposed as an effective strategy to increase protein production and mitigate the emissions to upgrade organic waste. This study isolated and identified 10 gut-derived bacteria with high ammonia-assimilation capacity from BSFL and further evaluated their functional impact on SCR biotransformation mediated by the BSFL system. The SCR + BSFL + mixed ammonia-assimilating microbial consortium group (DBM) showed a 7.71 % increase in peak larval biomass relative to the SCR+BSFL group (DB), demonstrating significant microbial synergy in waste valorization. Additionally, the DBM group reduced cumulative NH 3 emissions by 27.04 % compared to the DB group. Compared to the SCR group (D), DB group, and DM group, the DBM group achieved remarkable reductions in N 2 O emissions 99.69 %, 48.82 %, and 99.41 %, respectively. Furthermore, NH 4 + -N content in the DBM group was reduced by 15 % compared to the DM group at day 6. Analysis of substrate nitrogen composition and gene expression indicated that the DBM group primarily achieved nitrogen retention through ammonium assimilation, enhanced nitrification, and reduced denitrification processes. This study optimizes nitrogen management in BSFL technology, enhancing organic waste conversion efficiency and scaling insect protein production from soybean residue to advance circular economy and environmental sustainability. • 10 high-efficiency ammonia-assimilating microbes were screened from gut. • Efficient bioconversion was achieved through synergistic interaction between gut microbes and BSFL. • Functional microbes supplementation elevated larval biomass by 7.71 % through nitrogen allocation. • Gut ammonia-assimilating microbes reduced 27.04 % NH 3 emissions and 48.82 % N 2 O emissions. • Mitigation gas emissions had the significant correlation with gut ammonia-assimilating microbes.