Yeast Β-Glucan Enhances the Intestinal Immune Function in Coho Salmon Via the Modulation of Gut Microbiota-Mediated Lipid Metabolism

Aquaculture faces disease outbreaks that cause significant economic losses. Yeast (3- glucan, a bioactive component of yeast cell walls, enhances intestinal immune function, though its underlying mechanism remains unclear. Herein, this study used coho salmon (20.02 +/- 0.15 g), with yeast (3- glucan added to the basal diet at concentrations of 0, 125, 250, 500, and 1000 mg/kg. Each treatment group included three replicates, with 20 fish per replicate, and the cultivation period lasted for 8 weeks. This study demonstrated that the dietary inclusion of yeast (3- glucan significantly enhanced the growth performance of coho salmon and markedly improved intestinal physical barrier function, as evidenced by the upregulation of zo1, zo2, occludin, claudin15, and claudin19 gene expression. Additionally, it significantly strengthened the intestinal immune barrier, as reflected by the upregulated expression of IgD, IgM, IgT, il-15, and tgf-beta 1. Notably, our findings also suggest that the immunomodulatory role of yeast (3- glucan lies in its regulation of intestinal probiotics ( Clostridium sensu stricto 1 , Romboutsia, Bacillus, and Turicibacter), which mediate lipid metabolism, leading to the production of unsaturated fatty acids and antimicrobial peptides, thereby strengthening the host's ability to resist pathogenic invasions. Furthermore, in vitro experiments demonstrated that the intestinal mucus from coho salmon fed yeast (3- glucan significantly inhibited viral invasion. Our findings demonstrate that yeast (3- glucan enhances host immune function by improving the composition of the gut microbiota and its metabolic products, thereby alleviating virus-induced intestinal damage.