Effect of itaconic acid production on Neurospora crassa in consolidated bioprocessing of cellulose

Abstract

A system for itaconic acid synthesis from cellulose by Neurospora crassa was established, resulting in the highest yield of itaconic acid was 354.08 + 35.99 mg/L. Meanwhile, cellulase activity increased significantly, without any strain modifications for improved cellulase production. Multi-omics analyses showed that itaconic acid synthesis reduced energy production, leading to decreases in trehalose, cell wall, fatty acids synthesis and downregulations in MAPK signaling pathway, cell cycle and meiosis. More importantly, the low-energy environment enhanced the energy-efficient cellobionic acid/gluconic acid pathway, and the cellulase composition also changed significantly, manifested as the up-regulation of LPMOs and the down-regulation of β-glucosidases. Enhancing LPMOs-cellobionic acid/gluconic acid system has the potential to reduce energy consumption of the consolidated bioprocessing. These findings offer an overview of resource allocations by N. crassa in response to itaconic acid synthesis and highlight a series of intriguing connections between itaconic acid synthesis and cellulase synthesis in consolidated bioprocessing.

Improved consolidated bioprocessing for itaconic acid production by simultaneous optimization of cellulase and metabolic pathway of Neurospora crassa

“…To further increase the content of the precursor cis-aconite acid in the cytoplasm, the cis-aconite transporter MTTA from Aspergillus terreus was expressed on the basis of constructing the rGS. Our previous studies have shown that MTTA expression could significantly increase itaconic acid production [ 12 ]. Figure 4 E shows that the titer of strain PMF–CAD–MTTA was 356.4 mg/L, and the highest titer of PMF–CAD–MTTA–rGS was 637.2 mg/L, indicating that the rGS could further enhance the itaconic acid titer on the basis of the expression of MTTA.…”

“…The synthesis of itaconic acid weakened the TCA cycle and electron transport chain, which reduced the productivity of the entire system. Under the condition of low energy, the cellulase system was adjusted accordingly, which increased the synthesis of LPMOs related enzymes, and thus improved the overall cellulase activity [ 12 ]. Strain PMF–CAD–MTTA–TrCBH2 was constructed to further expressed the cellobiohydrolase 2 in the strain PMF–CAD–MTTA to improve the overall cellulase activity, thereby increasing the concentration of itaconic acid.…”

“…Our study showed that MTTA not only significantly increased itaconic acid production in improving the synthesis of N. crassa , but also caused metabolic changes that were sufficient to affect cellulase synthesis. MTTA is able to transport cis-aconitic acid accumulated in mitochondria to the cytoplasm, thereby introducing more carbon source from the oxidative branch of the TCA cycle into the itaconic acid synthesis pathway, resulting in the inflow of carbon source at the reducing end of the TCA cycle is reduced after the expression of MTTA [ 12 ]. In the TCA cycle, the conversion of 2-oxoglutaric acid to succinyl-CoA is irreversible, so the TCA cycle is irreversible in nature [ 51 ].…”

“…Filamentous fungi have great potential for breaking down lignocellulosic biomass, and most commercial cellulases and other biomass hydrolases are produced by them [ 10 , 11 ], which makes it more possible to establish an efficient single microbial CBP system. However, the challenges are also obvious, including efficient expression of various heterologous genes in the construction pathway, effective compatibility of the new pathway with the existing pathways in the cell to maximize the yield, and the balance between the secretion of cellulase and the synthesis of products [ 12 ].…”

Complexity of fungal polyketide biosynthesis and function

“…For instance, Aspergillus oryzae is a convenient host, because it is a GRAS (generally regarded as safe) organism and produces none or very few own polyketides. It has been used to decipher the alternariol biosynthesis (Wenderoth et al, 2019) and more recently for the production of basidiomycete polyketides (Han et al, 2023).…”