Host's P85 alpha genotype restructures the gut microbiota and regulates fat metabolism in gibel carp

There are indications that the intestinal microbiota, bile acids, lipid metabolism, and host genotype may all be interconnected, but their interrelationships are still only partially understood. In the present study, we designed three feeding trials and used gibel carp (Carassius auratus gibelio) as a model to investigate the interactions among all of the above parameters. In trial 1, we used wild-type (WT) and heterozygous pik3r1-deficient (P85+/-) fish (each n = 15) and found that the composition and structure of gut microbiota significantly differed between the two groups. The WT group exhibited a lower intestinal content of bile acids and increased physiological and histological parameters associated with obesity. Citrobacter freundii was significantly correlated with bile acid content. In trial 2, we supplemented two different levels of C. freundii GC01 strain to the WT fish diet: 106 (C6) and 109 (C9) cfu/kg (all n = 24). Experimental groups had lower obesity indices, but higher growth parameters, and bile acid content. As cholic acid was the most abundant bile acid in the gut of gibel carp, in trial 3 we supplemented it to the fish feed: the experimental group had lower obesity indices. In summary, the P85+/-genotype restructured intestinal microbiota and increased the abundance of C. freundii. This triggered a meta-bolic cascade: gut microbiota modulation affected the bile acid content, which then affected the lipid meta-bolism, and thereby obesity indices in fish. The intriguing observation that Citrobacter freundii GC01 appears to improve feed utilization in gibel carp, while simultaneously reducing lipid accumulation, deserves further studies aimed at potential application in aquaculture.