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Burst agitation rate promotes sustained semicontinuous cultivation of filamentous fungi in stirred tank reactors

Summary

Scientists improved the way shiitake mushrooms are grown in fermentation tanks by using a smart agitation strategy. Instead of constant stirring, they used periodic bursts of high-speed mixing to prevent clumping while maintaining healthy fungal growth. This approach increased the amount of usable biomass produced and allowed the fermentation to run longer without interruption, making mushroom cultivation more efficient and sustainable.

Background

Edible filamentous fungi like Lentinula edodes (shiitake mushrooms) are cultivated in submerged fermentation for biomass production. Control of mycelial morphology is critical to prevent bioreactor clogging, particularly in continuous cultures where fungal adhesion to surfaces can impair nutrient distribution and oxygen uptake. This study addresses the challenge of balancing adhesion control with shear stress minimization.

Objective

To develop a novel agitation strategy that controls mycelia adhesion while maximizing fungal biomass production in stirred tank reactors (STR) during batch and semicontinuous cultivation. The study optimized combinations of constant impeller speed, burst agitation duration, and burst frequency to improve cultivation efficiency.

Results

Optimal batch conditions achieved 4.95 g/L cell dry weight (CDW) with 4 bursts per day at 1500 RPM. Semicontinuous cultivation at dilution rate 0.02 h⁻¹ maintained 5.09 g/L CDW for 10 days without washout, producing 396 mg CDW/h (1.9-fold higher than batch). The richer medium enabled sustained growth at 0.025 h⁻¹ dilution rate with 470 mg CDW/h productivity. Fungal biomass contained up to 14% glucans with β-glucans predominating.

Conclusion

A combination of constant impeller agitation (400 RPM) with short high-speed bursts (1200-1500 RPM for 30 seconds, 4 times daily) effectively prevents mycelial clumping while maintaining biomass growth. This dynamic agitation strategy enables sustainable semicontinuous cultivation at dilution rates up to 0.025 h⁻¹, significantly improving volumetric productivity compared to batch fermentation and potentially applicable to other edible Agaricomycetes species.
  • Published in:Applied Microbiology and Biotechnology,
  • Study Type:Experimental Study,
  • Source: 10.1007/s00253-025-13579-y, PMID: 40826246
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