The dead-end filtration characteristics of the dimorphic yeast Kluyveromyces marxianus var. marxianus (formerly fragilis) NRRLy2415 were investigated for a range of mean cell morphologies, ranging from predominantly yeast-like to predominantly filamentous. Semiautomated image analysis was used to measure the mean cell specific surface area, Sv, and the mean ratio of cell length to equivalent cylindrical diameter, Ldm, in each broth. The method of Ju and Ho (Biotechnol. Bioeng. 1988, 32, 95-99) was used to show that for broths with Ldm values between 1.72 and 10.03, the voidage of cell pellets formed by centrifugation increased with increasing Ldm. In the pressure range 30-180 kPa, the specific filter cake resistance, alpha, was found to be related to pressure, DeltaP, through the equation alpha = alpha0(1 + kcDeltaP). The dependence of alpha0/Sv2 on Ldm was found to be qualitatively consistent with the pellet voidage data and the Carman-Kozeny equation. Considerably better agreement with the experimental data was obtained when the Kozeny constant, K, was treated as variable and related to Ldm through the equation K = 4.83 + 7.08 log10 Ldm. The cake compressibility constant, kc, was found to increase with increasing Ldm, a phenomenon consistent with the wide range of voidages that can be displayed by beds of long cylinders.
The effect of changing environmental conditions on the morphology of the yeast Kluyveromyces marxianus var. marxianus NRRLy2415 was investigated in batch and continuous culture, using a previously developed computer-aided image analysis protocol [O'Shea and Walsh (1996) Biotechnol Bioeng 51: 679 690]. The morphology of the organism is primarily controlled by the specific growth rate, mu. This finding was contrary to a previous investigation [Walker and O'Neill (1990) J Chem Tech Biotechnol 49: 75-89]. When the organism is cultured in batch with excess oxygen, mu can approach the maximum specific growth rate, microm, and the primary morphology of the culture is yeast-like. However, if the organism is cultured in a chemostat, thereby controlling the growth rate, the morphology reverts to a pseudohyphal form. This response is thought to be an adaptation by the organism to its environment, whereby it assumes a foraging form under adverse environmental conditions. The use of computer-aided image analysis made possible the discrimination of subtle morphological differences between samples and the determination of the relationship between morphology and growth rate.
A semiautomatic image analysis method has been developed to characterize the morphology of the dimorphic yeast Kluyveromyces marxianus var. marxianus (formerly fragilis) NRRLy2415 undergoing alcoholic fermentation of cheese whey permeate. The method is capable of separating cells into six defined categories, varying from simple ovoid yeast cells to branched mycelial cells. A sample size of 300 cells was found to be sufficient to obtain a statistically significant categorization. The processing time for a sample was found to be approximately 90 min. In addition to qualitative characterization, the method permits the measurement of geometric properties such as the width, length, and volume of individual cells or clusters of cells. When the cells analyzed by the automatic method were categorized on a manual basis, the error level in the automatic routine was found to be less than 3%.
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