Interaction between genetics and inulin affects host metabolism in rainbow trout fed a sustainable all plant-based diet.

Inulin affects nutrition and metabolism in many animals. Although inulin is widely used in the diet of teleosts, its mechanism of action is unknown. Here, we investigated the effect of inulin (2 %) on the intestinal microbiome and metabolism in rainbow trout () selected for growth and survival when fed a 100 % plant-based diet () and a control line (). Metabolic responses to the two factors (line and inulin) in liver, intestine, muscle and adipose were tissue-specific, with line and interaction between the two factors influencing overall expression in liver. In the intestine, inulin and line and in muscle, line influenced the expression of metabolic genes. Microbiota between the mucus and digestive contents was significantly different, with genera from being more abundant in the mucus, whereas genera from the and being more abundant in contents. Effect of inulin and interaction between factors on the microbiome was evident in contents. The significant taxa of control and inulin-fed groups differed greatly with and being significantly abundant in the inulin-fed group. There was a general trend showing higher levels of all SCFA in group with propionic acid levels being significantly higher. An operational taxonomic unit (OTU) belonging to the was significantly abundant in . The tissue-specific correlations between OTU and gene expression may indicate the link between microbiome and metabolism. Together, these results suggest that line and inulin impact the gene expression in a tissue-specific manner, possibly driven by specific OTUs enriched in inulin-fed groups and .