Transcriptomic Analysis of Lipid Accumulation in Mucor circinelloides WJ11 Under Submerged and Solid-State...

The oleaginous filamentous fungus Mucor circinelloides was extensively investigated for bio-oil production using submerged fermentation (SmF) and solid-state fermentation (SSF) techniques. SSF fermentation may offer advantages over SmF, largely due to the fungus's unique filamentous structure and the lower costs associated with this strategy. In this study, M. circinelloides strain WJ11 exhibited lower fatty acid (FA) content, reaching up to 12% in SSF compared with 24.1% in SmF after 120 h. Furthermore, transcriptomic analysis observed that 7615 genes were differentially expressed between the two fermentation methods, with 3891 genes upregulated and 3724 downregulated in SSF. Notably, genes encoding triglyceride-related synthases were significantly downregulated in WJ11. The mRNA levels of ATP-citrate lyase were also reduced, indicating a decreased supply of acetyl-CoA for fatty acid biosynthesis in SSF. Additionally, isoleucine and leucine metabolism do not contribute to acetyl-CoA production, further hindering FA synthesis. For NADPH production, which is crucial for FA biosynthesis, the pentose phosphate pathway (PPP) was significantly downregulated, and the activity of NADP⁺-dependent malic enzyme was also reduced under SSF. Additionally, the downregulation of key genes contributes to the glycerolipid pathway and FA biosynthesis during SSF, confirming a strong correlation between these pathways and lipid biosynthesis in WJ11.