Hydrolyzed Debaryomyces hansenii yeasts as paraprobiotics in fish: Omics-based characterization of Atlantic salmon gut during a natural pathogen outbreak in seawater stage

Feed additives are an alternative to improve fish performance and health (without compromising growth) during farming conditions. To determine the physiological effects of two hydrolyzed Debaryomyces hansenii yeasts (LAN4 and LAN6 from Lallemand SAS) on the gut of post-smolts Atlantic salmon (Salmo salar), an in vivo experiment was conducted (7 weeks in freshwater and 6 weeks in seawater) using 0.1 % LAN4 or LAN6 in diets for vaccinated fish. Coincidentally, a natural outbreak of Moritella viscosa (a bacterial fish pathogen) was reported at week 5 in seawater. Thus, the current study focus incorporated the disease-inflicted modulation of intestinal proteome and microbiota composition, which was estimated through metaproteomics and 16S rRNA sequencing, respectively. Results showed a detection of 1170 amplicon sequence variants (ASVs) belonging to 52 genera (modulated among dietary groups). Moreover, a positive correlation between LAN4 and control group (Ctr) was detected based on ASVs analysis. Regarding metaproteomics data and enrichment analysis (using KEGG or GO databases), LAN4 group showed a higher abundance of proteins linked to 48 functional terms such as amino acid biosynthesis and metabolism, immune homeostasis and cellular response to oxidative stress. On contrary, the proteins detected in LAN6 were linked with 14 terms (e.g., ferroptosis, arachidonic acid metabolism and regulation of cell projection assembly) that can be related to the inflammatory process. These results suggest the potential of D. hansenii yeasts as a paraprobiotics for the intestinal proteome and microbiota structure of Atlantic salmon. Therefore, D. hansenii is a promising feed additive for aquaculture-related species during the production cycle.