Functional Probiotic Intervention Reshapes Host Microbiota and Metabolite Profiles to Enhance Disease Resistance in Micropterus salmoides.

In this study, Lactobacillus plantarum, Bacillus subtilis, and their 1:1 mixture were introduced into the aquaculture system of Micropterus salmoides for a duration of 42 days. Subsequently, a challenge test with Aeromonas hydrophila was performed. The objective was to evaluate the immunomodulatory and microbiota-regulating effects of these probiotics, with emphasis on intestinal microbial composition and serum metabolome shifts in treated versus control groups before and after infection. Results revealed a significant reduction in the relative abundance of A. hydrophila in the intestines of probiotic-treated fish (p < 0.05). Histological observations indicated improved intestinal integrity in treated groups. Metabolomic analysis identified significant alterations in serum compounds, particularly in carboxylic acids, organic oxygen compounds, glycerophospholipids, and fatty acyl derivatives (p < 0.05). Post-challenge, levels of pro-inflammatory metabolites were significantly lower in probiotic groups compared to controls. Microbial network analysis showed increased community modularity and stability in treated fish, with key shifts toward dominant genera such as Plesiomonas. These findings demonstrate that L. plantarum and B. subtilis effectively modulate host gut microbiota, reshape systemic metabolite profiles, and enhance immune resilience against bacterial infection. The observed microbiota-metabolome interactions underline the potential of these probiotics as functional feed additives for promoting fish health. The study provides mechanistic insights supporting the broader application of probiotic interventions in aquaculture and functional food development.