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

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

Automated summary

In this study, it was found that Bacillus licheniformis FA6 can alter the gut microbiota composition of zebrafish and increase lipid accumulation. Moreover, it was shown that B. licheniformis FA6 promotes acetate production, leading to increased acetyl-CoA levels and lipid synthesis in the liver. Additionally, B. licheniformis FA6 downregulates genes involved in fatty acid beta-oxidation, thereby reducing fatty acid oxidation in the liver.