Comparative Transcriptomics Analysis of the Responses of the Filamentous Fungus to Different Carbon Sources.

The natural product pneumocandin B is the precursor of the antifungal drug caspofungin. We found that replacing glucose in the initial fermentation medium with 20 g/L fructose is more conducive to pneumocandin B production and biomass accumulation. In order to explore the mechanism of the different metabolic responses to fructose and glucose, we used each as the sole carbon source, and the results showed that fructose increased the total pneumocandin B yield and biomass by 54.76 and 13.71%, respectively. Furthermore, we analyzed the differences of gene expression and metabolic pathways between the two different carbon sources by transcriptomic analysis. When fructose was used as the carbon source, genes related to the pentose phosphate pathway (PPP), glycolysis and branched-chain amino acid metabolism were significantly upregulated, resulting in increased intracellular pools of NADPH and acetyl-CoA in for cell growth and pneumocandin B product synthesis. Interestingly, the pneumocandin B biosynthetic gene cluster and the genes of the TCA cycle were significantly downregulated, while the FAS genes were significantly upregulated, indicating that more acetyl-CoA was used for fatty acid synthesis. In particular, we found that excessive synthesis of fatty acids caused lipid accumulation, and lipid droplets can sequester lipophilic secondary metabolites such as pneumocandin B to reduce cell damage, which may also be an important reason for the observed increase of pneumocandin B yield. These results provide new insights into the relationship between pneumocandin B biosynthesis and carbon sources in . At the same time, this study provides important genomic information for improving pneumocandin B production through metabolic engineering strategies in the future.