<i>Candida utilis</i> yeast as a functional protein source for Atlantic salmon (<i>Salmo salar</i> 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.诸如产朊假丝酵母（Candida utilis）这类微生物配料，是已知具备免疫调节功效的功能性蛋白源；而大豆粕则会引发大西洋鲑（Salmo salar L.）远端肠道的豆粕诱导性肠炎。肠道局部的炎症或免疫调节刺激，可改变大西洋鲑的血浆蛋白质组（plasma proteome）特征。这类偏差可作为鱼类健康的有效指示指标，因此成为鱼类疾病诊断的潜在工具。本研究旨在探究饲喂非活性干燥产朊假丝酵母菌体日粮、大豆粕日粮，以及添加不同水平产朊假丝酵母的大豆粕复合日粮的大西洋鲑，其肠道局部组织应答与血浆蛋白组的变化情况。本研究以鱼粉基础日粮作为对照日粮。在鱼粉基础日粮中添加产朊假丝酵母，并不会改变远端肠道的形态、免疫细胞群或基因表达。低水平产朊假丝酵母与大豆粕联用，可调节远端肠道的免疫细胞群，并减轻豆粕诱导性肠炎的严重程度；而高水平添加产朊假丝酵母的干预效果则相对较弱。血浆蛋白质组学特征的变化显示不同日粮间存在差异，但并未发现可作为健康或疾病标志物的特定蛋白质。研究结果表明，产朊假丝酵母不会改变肠道形态或引发血浆蛋白质组的显著变化，因此可作为大西洋鲑日粮中兼具潜在功能特性的优质替代蛋白源。