Vibrio proteolyticus DCF12.2 postbiotic modulates intestinal metabolic and immune pathways in zebrafish

Postbiotics have recently emerged as a promising alternative to probiotics in aquaculture due to their improved safety, stability, and ease of application; however, the biological effects of postbiotics derived from Vibrio proteolyticus remain largely unexplored. In this study, we evaluated the impact of dietary supplementation with ethanol-inactivated V. proteolyticus DCF12.2 on the intestinal microbiota composition and transcriptomic profile of zebrafish (Danio rerio). Fish were fed a control diet (CTRL group) or a diet supplemented with 1% lyophilized ethanol-inactivated V. proteolyticus DCF12.2 (VP group) for 21 days. Alpha and beta diversity analyses exhibited no significant differences in overall gut microbial composition between dietary groups, nor at the phylum or genus level. However, differential abundance analysis at the amplicon sequence variant (ASV) level identified significant differences in ASVs affiliated with the genera Aeromonas, Delftia, Ralstonia, Shewanella, and Stenotrophomonas, which were enriched in fish receiving the VP diet (p < 0.0001). Despite these ASV-level shifts, predicted microbial metabolic functions did not differ significantly between treatments. In contrast, transcriptomic analysis via Gene Set Enrichment Analysis (GSEA) detected a clear host response: a significant downregulation of the cytokine-cytokine receptor interaction pathway and the upregulation of pathways related to nutrient metabolism, oxidative phosphorylation, and cellular biosynthesis in fish fed the VP diet (adjusted p < 0.05). These results suggest that dietary supplementation with postbiotics from V. proteolyticus DCF12.2 modulates intestinal metabolic and immune pathways without inducing major restructuring of the gut microbiota composition. Collectively, these findings provide new insights into host-postbiotic interactions and support the potential application of postbiotics from V. proteolyticus DCF12.2 as functional feed additives for sustainable aquaculture. KEY POINTS: • Postbiotic diet did not alter gut microbial diversity but induced ASV-level differences • Postbiotic diet upregulated nutrient metabolism, oxidative phosphorylation, and cellular biosynthesis • Cytokine-cytokine receptor signaling was downregulated by the postbiotic diet.