Integrated microbiota and metabolomic analysis demonstrates the growth-promoting effects of Lactobacillus plantarum in Nile tilapia (Oreochromis nilotica)

Lactobacillus plantarum, a well-characterized probiotic from terrestrial animals, shows promising effects on fish growth and lipid metabolism. However, its role in promoting protein deposition in fish remains unclear. In this study, 180 juvenile Nile tilapia were randomly assigned to two groups and fed for eight weeks with either a control diet (CK) or a diet supplemented with L. plantarum (LR). The results showed that L. plantarum significantly improved final body weight, weight gain rate, body length, carcass rate, intestinal index, whole-body protein content, and villus length (P < 0.05), accompanied by increased expression of growth-related genes and activation of the mechanistic target of rapamycin (mTOR) pathway. Conversely, the hepatosomatic index, condition factor, mesenteric fat index, hepatic lipid droplets, liver and serum triglycerides were significantly reduced (P < 0.05). The L. plantarum group exhibited downregulated expression of lipogenic genes and upregulation of genes involved in lipolysis, β-oxidation, and fatty acid transport (P < 0.05). Gut microbiota analysis revealed higher α-diversity and increased relative abundances of Pseudomonas and Diaphorobacter, while Cetobacterium, Aestuariivirga, and Aurantimicrobium at the genus level were reduced (P < 0.05). Metabolomic profiling showed elevated bile acids, uridine, phosphatidylcholine, and carnitine derivatives (P < 0.05). To confirm strain-specific effects, germ-free zebrafish were mono-colonized with L. plantarum, leading to suppressed lipogenesis and enhanced lipolysis and growth-related gene expression. Overall, L. plantarum promoted growth while simultaneously reducing fat accumulation, indicating a non-adipogenic growth-promoting effects in Nile tilapia.