Postbiotic potential of heat-inactivated Limosilactobacillus reuteri and its cell-free supernatant in protecting intestinal health of zebrafish.

Postbiotics are non-viable substances derived from probiotics, offering advantages including high stability, strong safety profiles, and broad-spectrum effects. The present study aims to investigate the impact of Limosilactobacillus reuteri postbiotics on the intestinal health of zebrafish. Zebrafish were fed basal diet supplemented with either 10⁷ CFU/g heat-inactivated L. reuteri (hLR) or corresponding cell-free L. reuteri supernatant (LRs) for 14 days. Compared to the control group (CT), villus height in the zebrafish foregut and midgut were increased in LRs group. In addition, intestinal superoxide dismutase activity was significantly enhanced in hLR group and LRs group. Gut microbiota analysis revealed that both the hLR and LRs groups exhibited increased OTUs richness, altered microbial community structure at the phylum and genus levels, and reduced abundance of potential pathogenic bacteria in the gut community structure. Moreover, transcriptome analysis indicated that the functional enrichment of differentially expressed genes in the hLR group was primarily focused on immune regulation, while that in the LRs group was mainly concentrated on cell cycle regulation. The present study found that different postbiotic components of L. reuteri exerted distinct effects on zebrafish intestinal health, providing crucial evidence for the application of L. reuteri postbiotics as an effective feed additive in aquaculture.