Bacillus licheniformis FA6 Affects Zebrafish Lipid Metabolism through Promoting Acetyl-CoA Synthesis and Inhibiting β-Oxidation

Abstract

The intestinal microbiota contributes to energy metabolism, but the molecular mechanisms involved remain less clear. Bacteria of the genus <i>Bacillus</i> regulate lipid metabolism in the host and are thus commonly used as beneficial probiotic supplements. In the present study, <i>Bacillus licheniformis</i> FA6 was selected to assess its role in modulating lipid metabolism of zebrafish (<i>Danio rerio</i>). Combining 16S rRNA high-throughput sequencing, micro-CT scan, metabolic parameters measurement, and gene expression analysis, we demonstrated that <i>B. licheniformis</i> FA6 changed the gut microbiota composition of zebrafish and increased both the Firmicutes/Bacteroidetes ratio and lipid accumulation. In terms of metabolites, <i>B. licheniformis</i> FA6 appeared to promote acetate production, which increased acetyl-CoA levels and promoted lipid synthesis in the liver. In contrast, addition of <i>B. licheniformis</i> lowered carnitine levels, which in turn reduced fatty acid oxidation in the liver. At a molecular level, <i>B. licheniformis</i> FA6 upregulated key genes regulating de novo fatty acid synthesis and downregulated genes encoding key rate-limiting enzymes of fatty acid β-oxidation, thereby promoting lipid synthesis and reducing fatty acid oxidation. Generally, our results reveal that <i>B. licheniformis</i> FA6 promotes lipid accumulation in zebrafish through improving lipid synthesis and reducing β-oxidation.