Postbiotic Dietary Supplementation with Sonicated Shewanella sp. SpPdp11 Improves Intestinal Status in Juvenile Senegalese Sole (Solea senegalensis)

The use of non-viable microbial preparations (postbiotics) is emerging as a safe alternative to probiotics in aquaculture. In this study, we investigated the impact of dietary inclusion of sonicated cells of the marine bacterium Shewanella sp. Pdp11 (SpPdp11) on the intestinal health of juvenile Senegalese sole (Solea senegalensis). Fish were fed a control diet or a diet supplemented with SpPdp11 postbiotic for 45 days, and their intestinal status was assessed using histological, transcriptomic, and microbiota analyses. Postbiotic supplementation improved intestinal morphology by widening villi and reducing lamina propria and epithelial height, suggesting enhanced barrier function. RNA-seq analysis revealed downregulation of inflammatory pathways, including ECM receptor interaction and PPAR signaling, together with activation of bile acid biosynthesis. 16 S rRNA profiling showed a marked shift in microbial composition, with decreased prevalence of opportunistic taxa such as Vibrio and Stenotrophomonas and enrichment of beneficial genera, including Acinetobacter, Pseudomonas, and Malacoplasma. These results provide evidence that marine-derived postbiotics can modulate host physiology and gut microbial communities without the risks associated with live probiotics. Sonicated SpPdp11 represents a promising biotechnological feed additive to support intestinal health, reduce inflammation, and promote sustainable aquaculture practices.