Nutrient–Microbiota Co-Regulation of Protein Conversion in Black Soldier Fly Larvae: The Role of Alkali-Soluble Protein and Gut Microbial Communities

Insect protein farming provides sustainable advantages in land efficiency, emission reduction, and bioconversion. A major challenge is optimizing nutrient composition to achieve cost-effective protein production. This study investigates the co-regulatory mechanism between alkali-soluble protein (SpA) and gut microbiota in black soldier fly larvae (Hermetia illucens) and their effect on protein conversion efficiency. Feeding trials with varying alfalfa/SpA ratios, a wheat middlings/alfalfa meal blend at a 5:0 ratio was identified as optimal for promoting larval protein accumulation. SDS-PAGE and 16S rRNA analyses revealed a strong positive correlation with larval crude protein (R²=0.82). Network analysis confirmed positive correlations among SpA, larval protein, Enterococcus (51%), and Ignatzschineria (44%) (p<0.05), suggesting that these taxa synergistically enhanced proteolysis via protease secretion (R²=0.85) and chitinase-mediated gut remodeling. Multi-linear regression modeling confirmed that SpA was a superior predictor of larval crude protein content compared to total nitrogen (TN), improving the model's coefficient of determination (R²) from 0.3961 to 0.822. these findings highlight SpA's higher bioavailability and its direct role in metabolic utilization. By integrating feed composition, microbiome function, and host metabolism, a regulatory network that drives larval protein biosynthesis was established. This study proposes targeted modulation of dietary SpA content as a precision nutrition strategy to enhance beneficial microbial communities, and maximizing protein conversion efficiency in BSFL ,scalable solution for sustainable insect protein production from organic waste.