Improved Mixing Properties of Stirred Fermentation of an Aspergillus oryzae Hyphal Dispersion Mutant

The complexity of mechanical and biological processes in filamentous fungal fermentation remains a major obstacle to improving product yield. We previously demonstrated that the AGΔ-GAGΔ strain of Aspergillus oryzae, lacking both α-1,3-glucan (AG) and galactosaminogalactan (GAG), had improved hyphal dispersion, reduced culture viscosity, and increased recombinant protein production. Here, we applied computational fluid dynamics (CFD) and multi-omics analysis to characterize the AGΔ-GAGΔ strain during fermentation in a stirred-tank bioreactor. CFD simulations revealed large gas cavities behind the impeller blades and severe compartmentalization in both wild-type and AGΔ-GAGΔ cultures. However, shear stress distribution was broader and gas cavity formation was lower in the AGΔ-GAGΔ strain than in the wild type. The simulation results were consistent with measurements of volumetric oxygen mass transfer coefficients (K_La) and mixing times. Transcriptome analysis revealed upregulation of TCA-cycle genes in AGΔ-GAGΔ relative to the wild type. Analysis of intracellular and extracellular metabolites indicated distinct metabolic profiles associated with oxygen availability. Our findings highlight the critical role of hydrodynamics in fungal fermentation and demonstrate the potential of strain engineering for improving mixing characteristics.