Effect of dietary niacin on immune response, apoptosis and microbial community in the intestine of juvenile turbot (Scophthalmus maximus L.)

A ten-week feeding trial was conducted to investigate the effect of dietary niacin on intestinal health of juvenile turbot. Three isonitrogenous and isolipidic experimental diets were formulated, containing 0 (NA0, as control), 20 (NA20), and 80 (NA80) mg/kg niacin, respectively. Compared with the NA0 group, dietary 20 mg/kg niacin significantly reduced the gene expression of NF-κB and pro-inflammatory cytokines (TNF-α, IFN-γ and IL-8), and increased the expression of TGF-β. Furthermore, dietary niacin at 20 mg/kg significantly decreased the gene expression of Caspase-9 and tumor suppressor p53, and increased the ratio of Bcl-2/Bax. Sequencing of intestinal bacterial 16 S rRNA V4 region revealed that dietary 20 mg/kg niacin significantly up-regulated the abundance of lactic acid bacteria (Lactobacillus, Streptococcus, Lactococcus, Leuconostoc and Enterococcus) and Anoxybacillus, and optimized the composition of intestinal bacterial community. However, diet NA80 increased the relative abundance of opportunistic pathogen Vibrio and Pseudomonas. Collectively, dietary niacin at 20 mg/kg is beneficial to gut health of juvenile turbot, however, excessive addition of niacin (80 mg/kg) showed negative effect on intestinal microbial communities. •Dietary niacin at 20 mg/kg enhanced the intestinal mucosal immune function of juvenile turbot.•Dietary niacin at 20 mg/kg improved the intestinal microbiota community of juvenile turbot.•The excessive addition of niacin (80 mg/kg) showed negative effect on intestinal bacterial community of juvenile turbot.