Bacillus subtilis HGCC-1 improves growth performance and liver health via regulating gut microbiota in golden pompano.

Probiotics as green inputs have been reported to regulate metabolism and immunity of fish. However, the mechanisms by which probiotics improve growth and health of fish are unclear. Therefore, the aim of this study was to investigate the effect of Bacillus subtilis HGCC-1, an indigenous probiotic isolated from fish, on growth performance, host lipid metabolism, liver inflammation and gut microbiota of golden pompano. 160,000 golden pompanos with the initial body weight of 93.6 ± 5.0 g was randomly assigned to two dietary groups: Control and HGCC-1 (control diet supplemented with 0.3 g/kg Bacillus subtilis HGCC-1 fermentation product), and after three weeks of feeding, 26 golden pompanos were randomly collected from each group for gut microbiome and host phenotype analysis. Dietary supplementation with Bacillus subtilis HGCC-1 significantly promoted growth performance (P < 0.05) and enhanced feed utilization. Besides, HGCC-1 improved liver health and alleviated hepatic steatosis and inflammation. Furthermore, Bacillus subtilis HGCC-1 enhanced intestinal lipid absorption, promoted hepatic utilization of dietary fat by improving hepatic lipid uptake/transport and fatty acid β-oxidation to provide energy, and reduced hepatic TG level (P < 0.05), which may be the potential mechanism of Bacillus subtilis HGCC-1-mediated growth promotion. Finally, Bacillus subtilis HGCC-1 significantly altered the structure and function of gut microbiota (P < 0.05), leading to enrichment of beneficial taxa such as Bacillus (P < 0.0001) and increased of the ratio of "Functional Group 2/Functional Group 1" (P = 0.00092). Interestingly, the ratio of "Functional Group 2/Functional Group 1" was linked to the growth traits (Spearman, P < 0.05), while the intestinal abundance of Bacillus was correlated with serum TG in fish (Spearman, R = 0.47, P = 0.00091), suggesting a role of the intestinal microbiota in HGCC-1 mediated effect on growth and lipid metabolism. In summary, Bacillus subtilis HGCC-1 promotes growth performance, alleviate hepatic steatosis and enhances liver health via regulating gut microbiota in golden pompano, which ultimately showed as beneficial effect of fish growth and health.