Unveiling thermotolerant and entomopathogenic fungi potential for solid-state fermentation: Multiscale evaluation in packed-bed bioreactor.

This work presents the production of fungal conidia from the thermotolerant and entomopathogenic fungi Metarhizium robertsii, by means of solid-state fermentation (SSF) in packed-bed bioreactors (PBR) up to a pilot scale of 100 L. The M. robertsii strain used (EAMa 01/158-su) presents both thermotolerant and entomopathogenic properties. Its thermotolerance is an unusual trait as entomopathogenic strain, and can help to surpass heat accumulation, the main limitation when increasing scale in SSF. Using a mixture of beer spent grains (BSG) and wood chips as substrates, work is performed at 3 different scales: laboratory (0.5 L), bench (22 L) and pilot (100 L). Air-filled porosity (AFP), specific airflow (sAF) and superficial velocity (VZ) were chosen as parameters to compare across scales. At 0.5 L, production time was optimised at 5 days. At 22 L, successful batch operation yielded homogeneous production throughout the packed bed. At pilot scale of 100 L, conidia production (conidia g-1BSG) and yield achieved were not significantly different from values achieved at 0.5 L, confirming the robustness of the process across reactor volumes. The results highlight the relevance of AFP, sAF and VZ as critical parameters for SSF reactor design and process evaluation and provide a basis for future industrial implementation of fungal SSF in PBR. This work validates thermotolerant entomopathogenic fungi as a viable strategy for industrial-scale SSF in packed-bed bioreactors, demonstrating the potential of thermotolerant entomopathogenic strains in fungal PBR conidia production by reaching pilot scale of 100 L.