Evaluation of the effect of host-derived Latilactobacillus sakei MG6 on the physiological health and intestinal homeostasis in turbot (Scophthalmus maximus L.)

Probiotics have been widely used in aquaculture. Host-derived probiotics offer advantages in intestinal adhesion and colonization. This study characterized probiotic properties of Latilactobacillus sakei MG6, a gut-derived strain, and evaluated its effects on immune modulation, nutrient metabolism, and intestinal microbiota community of turbot (Scophthalmus maximus). Samples were collected at the following time points: CON (day 0, diet without MG6 supplementation), days L1-7 (days 1, 2, 3, and 7, turbots fed diets with MG6 supplementation), and days S3-7 (days 3 and 7, after post-cessation). In vitro assays revealed that L. sakei MG6 exhibited strong acid tolerance, bile salt resistance, and high auto-aggregation. And the cell-free supernatant of L. sakei MG6 showed antimicrobial activity against Vibrio anguillarum, Vibrio alginolyticus, and Vibrio scophthalmi. In vivo, the results demonstrated that compared to CON, dietary MG6 significantly enhanced respiratory burst activity at days L1 and S3, increased serum total protein, albumin, and globulin levels at day L1. The expressions of immune related genes IL-8, IL-1β, IL-10, TGF-β, MHC-I, and IFIH1 in the head kidney were also upregulated by dietary MG6 at days L3 and L7. Concurrently, the digestive enzyme activities were also significantly elevated by MG6 at days L3 and L7. Dietary MG6 reshaped gut microbial community, with L7 exhibiting enriched microbial diversity, stabilized co-occurrence networks, and positive correlations with nutrient metabolism pathways. However, the turbot showed disrupted intestinal homeostasis and impaired nutrient absorption at S3. These results demonstrated that L. sakei MG6 can effectively colonize the turbot intestine, synergistically enhance immune function, metabolic efficiency, and intestinal microbial resilience, supporting its application as a functional feed additive for sustainable aquaculture. The alternate feeding strategy of MG6 (Cessation of MG6 supplementation) induces intestinal dysbiosis and metabolic dysregulation in turbot, whereas continuous MG6 supplementation may demonstrate superior benefits for host health.