Cyberlindnera jadinii yeast as a functional protein source for Atlantic salmon (Salmo salar L.): Early response of intestinal mucosal compartments in the distal intestine.

The interplay between nutrition and the immune system is well recognized, and several studies show that experimental diets elicit local morphological changes and alteration of gene and protein expression in the intestinal mucosa of Atlantic salmon. In this study the pathophysiological effects of experimental diets on mucosal responses in the distal intestine of Atlantic salmon were investigated. Atlantic salmon were fed diets with inclusion of soybean meal (SBM) and Cyberlindnera jadinii (CJ) yeast for 7 days. A standard fish meal (FM) diet was used as a control. Morphological, immunohistochemical and gene expression analyses were used to evaluate the presence of immune cells, proliferating cells, and stem cell populations in mucosal compartments of the simple folds in the distal intestine. Fish fed SBM developed morphological changes consistent with SBM induced enteritis. Immunohistochemistry showed an increased presence of apoptotic cells, CD3ϵ and CD8α labelled cells in the simple fold epithelium of SBM group compared with the CJ group. For the investigated genes, expression levels in all three groups were mostly higher in the epithelial compartment of the simple fold than in the compartment beneath the folds. Most changes within the epithelial compartment were observed in fish fed SBM, where expression of CD3ζ, CD8α, MHC I and MHC II were lower than the FM control group. The CJ group had an increased expression of the stem cell marker Lgr5 in the epithelial compartment compared with SBM group. The division of the simple fold into an apical and basal compartment showed that the increase in Lgr5 was evident along the whole length of the simple folds and not confined to the base of the folds. Similarly, proliferation (PCNA, MCM2) and apoptosis (Caspase-3) gene expression was present in the entire length of the simple folds, suggesting that intestinal epithelial cell turnover is not confined to the basal or apical part of the fold. This study shows that the epithelial compartment is active in the early immunoregulatory response towards dietary stimuli and that the level of an intestinal stem cell marker in salmon was influenced by a diet containing CJ yeast.

Candida utilis yeast as a functional protein source for Atlantic salmon (Salmo salar L.): Local intestinal tissue and plasma proteome responses.

Microbial ingredients such as Candida utilis yeast are known to be functional protein sources with immunomodulating effects whereas soybean meal causes soybean meal-induced enteritis in the distal intestine of Atlantic salmon (Salmo salar L.). Inflammatory or immunomodulatory stimuli at the local level in the intestine may alter the plasma proteome profile of Atlantic salmon. These deviations can be helpful indicators for fish health and, therefore potential tools in the diagnosis of fish diseases. The present work aimed to identify local intestinal tissue responses and changes in plasma protein profiles of Atlantic salmon fed inactive dry Candida utilis yeast biomass, soybean meal, or combination of soybean meal based diet with various inclusion levels of Candida utilis. A fishmeal based diet was used as control diet. Inclusion of Candida utilis yeast to a fishmeal based diet did not alter the morphology, immune cell population or gene expression of the distal intestine. Lower levels of Candida utilis combined with soybean meal modulated immune cell populations in the distal intestine and reduced the severity of soybean meal-induced enteritis, while higher inclusion levels of Candida utilis were less effective. Changes in the plasma proteomic profile revealed differences between the diets but did not indicate any specific proteins that could be a marker for health or disease. The results suggest that Candida utilis does not alter intestinal morphology or induce major changes in plasma proteome, and thus could be a high-quality alternative protein source with potential functional properties in diets for Atlantic salmon.