Effect of biomass concentration and mycelial morphology on fermentation broth rheology.

The effect of biomass concentration and mycelial morphology on fungal fermentation broth rheological properties has been investigated. In previous work it had been shown that commonly used rheological parameters, such as the power law consistency and flow behavior indices, could be correlated successfully with the broth biomass concentration and clump morphological parameters of roughness and compactness. More recent work on a broader range of data showed a correlation between roughness and compactness; consequently, it was not correct to use both of these morphological variables simultaneously in rheological parameter correlations. Furthermore, earlier correlations were only made using clump morphological parameters, as clumps were found to be around 90% of the biomass in batch fermentations. In the present work it was found that the percentage of clumps fell to around 30% to 40% of a sample during the later stages of fed-batch fermentations. No clear relationship between the flow behavior index and biomass concentration was found, at least for those phases of the fermentation in which the viscosities were high enough for the rheology to be characterized by a disk turbine rheometer. The mean value of the flow behavior index was found to be 0.35 +/- 0.1 (standard deviation) throughout both batch and fed-batch fermentations, although some significant deviations from this value were observed early and very late in the fermentations. Correlations for the consistency index, measured using a disk turbine rheometer, were based on the biomass concentration and the mycelial size (represented by the mean projected area or the mean maximum dimension of all the mycelia). These correlations were reasonably successful for both fed-batch and batch fermentations. The correlation using the mean maximum dimension was preferred to that using the mean projected area, as the former is independent of magnification. The proposed correlation is: where K is the consistency index (Pa. s(n>)), C(m) is the biomass concentration as dry cell weight (g L(-1)), and D is the mean maximum dimension (microm). It should be noted that small changes in the exponent on the biomass concentration (alpha) may dramatically affect any predictions. Consequently, caution in the use of this correlation (and that based on mean projected area) is advocated, although its accuracy may be suitable for operational or design purposes.

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

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.

Measurement of hybridoma cell number, viability, and morphology using fully automated image analysis.

A novel automated image analysis method is described for characterizing the viability and morphology of animal cells from suspension cultures. With the aid of the exclusion dye Trypan Blue, the total and viable cell counts and the percentage of dead cells present are found. The area, perimeter, equivalent diameter, and circularity of the projected image of each cell are also measured, allowing the estimation of cell volume. The image analysis method is inherently sensitive, precise, consistent (non-operator dependent) and relatively fast, taking approximately 22 min to analyze one sample. The data it gives on individual cellular activity, as characterized by Trypan Blue uptake and cell morphology, are valuable in allowing early diagnosis of even subtle changes in the health of a culture. The method should permit better optimization of culture conditions, and will provide data for the modeling of cell population dynamics. As the conventional manual method is operator dependent, relatively limited in the amount of information it provides, and has a tendency to underestimate Trypan Blue takeup, it is suggested that image analysis be the preferred option for animal cell counting and viability determinations.

Correlation of Aspergillus niger broth rheological properties with biomass concentration and the shape of mycelial aggregates.

Aspergillus niger was grown in a 7-L chemostat at biomass levels of 7 to 9 gL(-1); dilution rates of 0.03, 0.05, 0.075, and 0.009 h(-1); and dissolved oxygen tensions of 7%, 12%, and 40% of air saturation. Broth rheological measurements were made on-line, while off-line image analysis was used to measure mycelial morphology, including characterization of mycelial aggregates (clumps). Under all conditions, more than 87% of the hyphase were in clumps, the shape of which determined the rheological characteristics of the broth. In particular, the power law consistency index could be correlated with the biomass concentration and the roughness factor of the clumps, which describes their hairiness. A decrease in specific growth rate decreased roughness, possibly due to changes in the amount of clump breakup. However, decreases of roughness with increasing dissolved oxygen tension might rather imply some effect on hyphal-hyphal interactions within the clumps.