Nutrient-Microbiota Co-Regulation of Protein Conversion in Black Soldier Fly Larvae: The Role of Alkali-Soluble...

Insect protein farming offers sustainable advantages in land efficiency, emission reductions, and bioconversion, yet optimizing the nutrient composition remains a major challenge for cost-effective production. This study investigates the co-regulatory mechanism between alkali-soluble protein (SpA) and the gut microbiota in black soldier fly larvae (Hermetia illucens) and their effect on protein conversion efficiency. Feeding trials with varying alfalfa/SpA ratios identified a wheat middlings/alfalfa meal blend at a (5:0 ratio) as optimal for promoting larval protein accumulation. SDS-PAGE and 16S rRNA analyses revealed a strong positive correlation between SpA and larval crude protein (R² = 0.82). The network analysis and Pearson correlation heatmap further confirmed positive correlations among SpA, larval protein, Enterococcus, and Ignatzschineria (p < 0.05), suggesting that high SpA in the substrate was associated with the enrichment of these taxa, which synergistically enhanced proteolysis through alkaline protease secretion (R² = 0.85) and chitinase-mediated gut remodeling. Multi-linear regression modeling verified SpA as a superior predictor of the crude protein content compared with total nitrogen (TN), improving the model's coefficient of determination (R²) from 0.40 to 0.82. These findings highlight SpA's higher bioavailability and its direct role in metabolic utilization. By integrating the feed composition, microbiome function, and host metabolism, this study established a regulatory network driving larval protein biosynthesis. The targeted modulation of dietary SpA content may offer a promising approach to enhance beneficial microbial communities and improve protein conversion efficiency in BSFL-rearing systems. These findings provide a theoretical basis for optimizing feed formulations to support sustainable insect protein production from organic waste.