Effect of supplementation of solid-state fermentation product of Bacillus subtilis HGcc-1 to high-fat diet on growth, hepatic lipid metabolism, epidermal mucus, gut and liver health and gut microbiota of zebrafish

This study investigated the effect of solid-state fermentation product of Bacillus subtilis HGcc-1 supplementation in a high-fat diet (HFD) on growth, hepatic lipid metabolism, epidermal mucus, gut and liver health and gut microbiota in zebrafish (Danio rerio). Two-month-old zebrafish were fed four experimental diets: normal diet (Normal), high-fat diet (HFD), and high-fat diet supplemented with 0.5% and 1.0% solid-state fermentation product of Bacillus subtilis HGcc-1 (abbreviation: 0.5% HGcc-1 and 1.0% HGcc-1, respectively) for 4 weeks. The results showed that HFD-feeding significantly increased hepatic lipid deposition compared to that in the Normal group. The addition of 1.0% HGcc-1 ameliorated the HFD-induced hepatic steatosis. Both 0.5% and 1.0% HGcc-1 supplementation significantly decreased the expression of lipogenesis genes (c/ebpα, fas, acc1 and dgat2), and increased the expression of lipolysis genes (ucp2, pparα). HFD supplemented with 1.0% HGcc-1 significantly improved the epidermal mucosal total antioxidant enzymes activity, lysozyme and complement levels compared with Normal and HFD groups. HFD-feeding significantly upregulated the expression of pro-inflammatory cytokine (il-1β, il-6) and down-regulated the expression of anti-inflammatory cytokines (il-10, tgf-β) both in liver and intestine. While the expression of pro-inflammatory cytokines (il-1β, il-6) in 0.5% and 1.0% HGcc-1 groups were remarkably down-regulated, and the expression of anti-inflammatory cytokines (il-10, tgf-β) were significantly up-regulated in 1.0% HGcc-1 group. HFD-feeding significantly down-regulated the expression of intestinal hif1α and tight junction proteins (claudin 7 and occludin 2) compared with Normal group. However, the expression of intestinal hif1α and tight junction proteins (claudin 7 and occludin 2) were significantly up-regulated in 1.0% HGcc-1 group. Compared with the HFD group, the addition of 0.5% and 1.0% HGcc-1 could significantly alleviate the intestinal oxidation. HFD-feeding significantly down-regulated the expression of antioxidant genes (nrf2, ho-1, cat, sod and gst). However, the expression of these antioxidant genes was significantly up-regulated in the 1.0% HGcc-1 group. Moreover, HGcc-1 supplementation at both levels increased the abundance of intestinal Fusobacteriota and Cetobacterium. In conclusion, high-fat diet induced negative effects in zebrafish, and dietary supplementation with 0.5% or 1.0% HGcc-1 decreased hepatic lipid deposition, enhanced epidermal mucus immunity, improved liver and intestine health, and modified gut microbiota homeostasis in zebrafish. The best positive effect was observed in zebrafish fed 1.0% solid-state fermentation of Bacillus subtilis HGcc-1 supplemented diet.