Transcriptomic Analysis Revealed the Differences in Lipid Accumulation between Spores and Mycelia of Mucor circinelloides WJ11 under Solid-State Fermentation

The oleaginous fungus Mucor circinelloides has been studied for microbial oil production. Solid-state fermentation may be more suitable for lipid production than submerged fermentation due to its special filamentous structure and lower fermentation costs. M. circinelloides WJ11 under solid-state fermentation indicated that the total fatty acid content of mycelia was significantly higher than that of spores (15.0 and 10.4% in mycelia and spores after 192 h, respectively), while the biomass of the fungal mycelia was lower than that of the spores, reaching 78.2 and 86.9 mg/g, respectively. Transcriptomic studies showed that a total of 9069 genes were differentially expressed between spores and mycelia during solid-state fermentation, of which 4748 were up-regulated and 4321 were down-regulated. Among them, triglyceride-related synthases in M. circinelloides were significantly up-regulated in the mycelia. The mRNA expression level of ATP: citrate lyase was obviously increased to provide more acetyl-CoA for fatty acid synthesis in mycelia, moreover, the metabolism of leucine and isoleucine can also produce more acetyl-CoA for lipid accumulation in M. circinelloides. For NADPH supply, the expression of the pentose phosphate pathway was significantly up-regulated in mycelia, while NADP(+)-dependent malic enzyme was also increased by 9.5-fold under solid-state fermentation. Compared with gene expression in spores, the autophagy pathway was clearly up-regulated in mycelia to prove that autophagy was related to lipid accumulation in M. circinelloides.

Automated summary

During solid-state fermentation, the oleaginous fungus Mucor circinelloides showed higher fatty acid content in mycelia compared to spores, although mycelia had lower biomass. Transcriptomic analysis revealed differential gene expression between spores and mycelia, including up-regulation of triglyceride-related synthases, ATP: citrate lyase, and leucine and isoleucine metabolism in mycelia. Autophagy pathway was also up-regulated in mycelia, suggesting its involvement in lipid accumulation in M. circinelloides.