Application of antimicrobial peptides expressed by Tetraselmis subcordiformis (Wille) butcher improves the health of turbot via oral administration.

To mitigate bacterial infections in aquaculture caused by antibiotic overuse, two highly effective antimicrobial peptides, AS-CATH4 and ALFPm3, were introduced into turbot aquaculture in this study. A microalgal chloroplast expression system was established in Tetraselmis subcordiformis through tandem expression of these two exogenous antimicrobial peptides. This system was then used to produce microalgal feed for turbot (Scophthalmus maximus L.). The in vitro antimicrobial capacity and in vivo functional effects on turbot were evaluated. The results indicated that the engineered microalgal strain (ASD) containing the two antimicrobial peptides stably expressed these peptides and exhibited inhibitory effects against Staphylococcus aureus, Vibrio parahaemolyticus, and V. splendens. Feeding turbot with commercial feed mixed with ASD downregulated inflammatory factors such as TNF-α, IL-1β, and IL-8R in the gut and liver of turbot, thereby modulating inflammatory responses. Simultaneously, this treatment modulated the dynamic equilibrium of the gut microbiota by remodeling the abundance and diversity of gut bacteria. In conclusion, this study provides strong evidence for the use of microalgae oral delivery systems to deliver antimicrobial peptides, thereby enhancing the immunity of aquatic organisms and regulating the function of their gut microbiota.