Dependence of mycelial morphology on impeller type and agitation intensity

Abstract

The influence of the agitation conditions on the morphology of fenicillium chrysogenum (freely dispersed and aggregated forms) was examined using radial (Rushton turbines and paddles), axial (pitched blades, propeller, and Prochem Maxflow T), and counterflow impellers (Intermig). Culture broth was taken from a continuous fermentation at steady state and was agitated for 30 min in an ungassed vessel of 1.4-L working volume. The power inputs per unit volume of liquid in the tank, fNL, ranged from 0.6 to 6 kW/m3. Image analysis was used to measure mycelial morphology. To characterize the intensity of the damage caused by different impellers, the mean total hyphal length (freely dispersed form) and the mean projected area (all dispersed types, i.e., also including aggregates) were used. [In this study, breakage of aggregates was taken into account quantitatively for the first time.] At 1.4-L scale and a given PNL, changes in the morphology depended significantly on the impeller geometry. However, the morphological data (obtained with different geometries and various f/VL) could be correlated on the basis of equal tip speed and two other, less simple, mixing parameters. One is based on the specific energy dissipation rate in the impeller region, which is simply related to fNL and particular impeller geometrical parameters. The other which is developed in this study is based on a combination of the specific energy dissipation rate in the impeller swept volume and the frequency of mycelial circulation through that volume. For convenience, the function arising from this concept is called the "energy dissipation/circulation" function.To test the broader validity of these correlations, scaleup experiments were carried out in mixing tanks of 1.4, 20, and 180 L using a Rushton turbine and broth from a fed-ba t c h f e r m e n t at i o n . T h e e n e rg y d i ssi patio n/ci rc ulation function was a reasonable correlating parameter for hyphal damage over this range of scales, whereas tip speed, fNL, and specific energy dissipation rate in the impeller region were poor. Two forms of the energy dissipationhirculation function were considered, one of which additionally allowed for the numbers of vortices behind the blades of each impeller type. Although both forms were successful at correlating the data for the standard impeller designs considered here, there was preliminary evidence that allowing for the vortices would be valuable. 0 1996 John Wiley & Sons, Inc.

Fungal morphology and fragmentation behavior in a fed-batchAspergillus oryzae fermentation at the production scale

“…1, Table II) has been found to correlate better with morphological and fragmentation data than power (P) per unit volume (V L ) (Justen et al, 1996(Justen et al, , 1998bAmanullah et al, 1999), impeller power is reported in terms of EDCF. For each sample time, EDCF was determined for each of the three impellers in the particular tank.…”

“…In stirred bioreactors, impeller shear stress often prevents cells from forming pellets and visual inspection in many processes shows dispersed growth being much more prevalent (Tucker et al, 1992;Olsvik and Kristiansen, 1994). Studies have shown that in these cases the vast majority of biomass resides in clumps (Tucker et al, 1992;Justen et al, 1996;Amanullah et al, 1999). However, most of these observations have come from laboratory or pilot-scale fermentations.…”

Influence of buffer systems on Trichoderma reesei Rut C-30 morphology and cellulase production

“…Pellets are spherical or ellipsoidal masses of hyphae with variable internal structure, ranging from loosely packed hyphae, forming ''fluffy'' pellets, to tightly packed, compact, dense pellets (Papagianni, 2004). The dispersed form consists of branched and unbranched hyphae (freely dispersed) and aggregates (clumps) (Justen et al 1996). The exact mechanism behind pellet formation is not known, and the mechanism probably varies from species to species, perhaps even from strain to strain.…”

Image analysis of the morphology of filamentous micro-organisms

“…It should be noted that Justen et al (1996) used projected area to describe of the dispersed forms in their agitation trials. Clearly, one method for all forms would be valuable.…”