HYDRODYNAMIC, PHYSIOLOGICAL, AND MORPHOLOGICAL-CHARACTERISTICS OF FUSARIUM-MONILIFORME IN GEOMETRICALLY DISSIMILAR STIRRED BIOREACTORS

The influence of two mixing geometries (at the same scale) with differ ent flow energy distributions on the performance of the gibberellic ac id fermentation and on the morphology of the producing fungus Fusarium moniliforme was investigated. Fermentations were performed using a tu rbine mixing system (TMS) and a counterflow mixing system (CMS), which were high and low power number mixing systems, respectively. Differen t agitator speed rate profiles were maintained to obtain equal specifi c power inputs to both mixing systems. Substantial differences in morp hology and productivity of F. moniliforme were found. To investigate t he causes of these differences, local values and spectra of the kineti c energy of flow fluctuations were measured during the fermentations u sing a stirring intensity measuring device (SIMD) and a frequency spec trum analyzer. Biomass and gibberellic acid concentrations were found to be higher in the TMS, where the energy distribution was less even, and where 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 larg er area, perimeter, and roughness was observed in the TMS. A correlati on between the morphology and productivity was found, and TMS favored the development of more productive mycelia with longer and thinner hyp hae. Introduced power was not a good parameter to characterize differe nt impellers, even at a given scale. (C) 1995 John Wiley & Sons, Inc.