Hydrodynamic, physiological, and morphological characteristics of Fusarium moniliforme in geometrically dissimilar stirred bioreactors

Abstract

The influence of two mixing geometries (at the same scale) with different flow energy distributions on the performance of the gibberellic acid fermentation and on the morphology of the producing fungus Fusarium moniliforme was investigated. Fermentations were performed using a turbine mixing system (TMS) and a counterflow mixing system (CMS), which were high and low power number mixing systems, respectively. Different agitator speed rate profiles were maintained to obtain equal specific power inputs to both mixing systems. Substantial differences in morphology and productivity of F. moniliforme were found. To investigate the causes of these differences, local values and spectra of the kinetic energy of flow fluctuations were measured during the fermentations using a stirring intensity measuring device (SIMD) and a frequency spectrum analyzer. Biomass and gibberellic acid concentrations were found to be higher in the TMS, where the energy distribution was less even, and Vi/here the main part of the energy was at small frequencies (large eddies). An automated image analysis method was used for quantitative characterization of F. moniliforme freely dispersed mycelia and clump morphology. A higher proportion of clumped mycelia with clumps of larger area, perimeter, and roughness was observed in the TMS. A correlation between the morphology and productivity was found, and TMS favored the development of more productive mycelia with longer and thinner hyphae. Introduced power was not a good parameter to characterize different impellers, even at a given scale.