Morphology-Rheology Coupling Enables Predictive Optimization of Hirsutella sinensis Submerged Fermentation: A Case...

Hirsutella sinensis, the anamorph of Ophiocordyceps sinensis, is a valuable medicinal fungus, yet its industrial production is constrained by low fermentation efficiency and poorly controlled mycelial morphology. In this study, morphology engineering strategies based on inoculum volume and microparticle-enhanced cultivation were systematically investigated to improve fermentation performance. Increasing inoculum volume (4%-10%, v/v) promoted a transition from dense (L-type) to loose (S-type) pellets, enhancing internal mass transfer and increasing biomass up to 18.7 g/L (compared to 11.1 g/L at 4% inoculum). Among the tested microparticles, talc exhibited the strongest effect, increasing biomass by 1.45-fold compared to the control without microparticles and significantly enhancing adenosine and mannitol production. Microscopic and elemental analyses revealed that talc modifies pellet architecture via mechanical embedding and structural disruption, leading to increased internal porosity. Quantitative models linking morphology (S%, L%, density H) and rheology (Ln viscosity) to biomass achieved high predictive accuracy (R² up to 0.92). Notably, a cross-process model demonstrated that morphology descriptors can serve as predictive state variables across different engineering strategies. Scale-up in a 5 L bioreactor further validated the approach, with a semi-continuous process achieving 44.68 g/week productivity (compared to 25.93 g/week for batch fermentation, an 73% increase). This study establishes a morphology-rheology-performance framework for H. sinensis and provides a methodological insight applicable to other filamentous fermentation systems.