DEPENDENCE OF PENICILLIUM-CHRYSOGENUM GROWTH, MORPHOLOGY, VACUOLATION, AND PRODUCTIVITY IN FED-BATCH FERMENTATIONS ON IMPELLER TYPE AND AGITATION INTENSITY

The influence of the agitation conditions on the growth, morphology, v acuolation, and productivity of Penicillium chrysogenum has been exami ned in 6 L fed-batch fermentations. A standard Rushton turbine, a four -bladed paddle, and a six-bladed pitched blade impeller were compared. Power inputs per unit volume of liquid, P/V-L, ranged from 0.35 to 7. 4 kW/m(3). The same fermentation protocol was used in each fermentatio n, including holding the dissolved oxygen concentration above 40% air saturation by gas blending. The mean projected area (for all dispersed types, including clumps) and the clump roughness were used to charact erize the morphology. Consideration of clumps was vital as these were the predominant morphological form. For a given impeller, the batch-ph ase specific growth rates and the overall biomass concentrations incre ased with agitation intensity. Higher fragmentation at higher speeds w as assumed to have promoted growth through increased formation of new growing tips. The mean projected area increased during the rapid growt h phase followed by a sharp decrease to a relatively constant value de pendent on the agitation conditions. The higher the speed, the lower t he projected area for a given impeller type. The proportion by volume of hyphal vacuoles and empty regions decreased with speed, possibly du e to fragmentation in the vacuolated regions. The specific penicillin production rate was generally higher with lower impeller speed for a g iven impeller type. The highest value of penicillin production as well as its rate was obtained using the Rushton turbine impeller at the lo west speed. At given P/V-L, changes in morphology, specific growth rar e, and specific penicillin production rate depended on impeller geomet ry. The morphological data could be correlated with either tip speed o r the ''energy dissipation/ circulation function,'' but a reasonable c orrelation of the specific growth rate and specific production rate wa s only possible with the latter. (C) 1998 John Wiley & Sons, Inc.