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  • Biochemistry and Biotechnology  (9)
  • 1995-1999  (9)
  • 1940-1944
  • 1
    Electronic Resource
    Electronic Resource
    Effect of agitation intensities on fungal morphology of submerged fermentation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 715-726 
    Details
    ISSN: 0006-3592
    Keywords: fungal morphology ; pellets ; hyphae ; hair of pellets ; agitation intensity ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Both parallel fermentations with Aspergillus awamori (CBS 115.52) and a literature study on several fungi have been carried out to determine a relation between fungal morphology and agitation intensity. The studied parameters include hyphal length, pellet size, surface structure or so-called hairy length of pellets, and dry mass per-wet-pellet volume at different specific energy dissipation rates. The literature data from different strains, different fermenters, and different cultivation conditions can be summarized to say that the main mean hyphal length is proportional to the specific energy dissipation rate according to a power function with an exponent of -0.25 ± 0.08. Fermentations with identical inocula showed that pellet size was also a function of the specific energy dissipation rate and proportional to the specific energy dissipation rate to an exponent of -0.16 ± 0.03. Based on the experimental observations, we propose the following mechanism of pellet damage during submerged cultivation in stirred fermenters. Interaction between mechanical forces and pellets results in the hyphal chip-off from the pellet outer zone instead of the breakup of pellets. By this mechanism, the extension of the hyphae or hair from pellets is restricted so that the size of pellets is related to the specific energy dissipation rate. Hyphae chipped off from pellets contribute free filamentous mycelia and reseed their growth. So the fraction of filamentous mycelial mass in the total biomass is related to the specific energy dissipation rate as well.To describe the surface morphology of pellets, the hyphal length in the outer zone of pellets or the so-called hairy length was measured in this study. A theoretical relation of the hairy length with the specific energy dissipation rate was derived. This relation matched the measured data well. It was found that the porosity of pellets showed an inverse relationship with the specific energy dissipation rate and that the dry biomass per-wet-pellet volume increased with the specific energy dissipation rates. This means that the tensile strength of pellets increased with the increase of specific energy dissipation rate. The assumption of a constant tensile strength, which is often used in literature, is then not valid for the derivation of the relation between pellet size and specific energy dissipation rate. The fraction of free filamentous mycelia in the total biomass appeared to be a function of the specific energy dissipation in stirred bioreactors. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 715-726, 1997.
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  • 2
    Electronic Resource
    Electronic Resource
    Metabolism of halogenated compounds in the white rot fungus Bjerkandera adusta studied by membrane inlet mass spectrometry and tandem mass spectrometry (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 51 (1996), S. 23-32 
    Details
    ISSN: 0006-3592
    Keywords: halogenated compounds ; basidiomycetes ; Bjerkander adusta ; flavors ; membrane inlet mass spectrometry (MIMS) ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Membrane inlet mass spectrometry has been used for the characterization of halogenated organic compounds produced by the fungus Bjerkandera adusta. Using this technique we obtained electron impact-, chemical ionization-, electron capture negative chemical ionization-mass spectra and tandem mass spectra directly from the growth medium. Through this direct analysis of the samples we identified novel bioconversion products and confirmed recently published data on the production of both chlorinated and brominated methoxybenzaldehyde metabolites. Growth profiles of the culture grown on a defined medium showed that the production of secondary metabolites starts after approximately 6 days and reaches maximal concentrations of 25-250 μM after 15-20 days. Although delayed, the production of secondary metabolites paralleled a depletion of glucose from the medium and stopped shortly after all glucose had been consumed. Experiments in which fluoro- and bromo-labeled 4-methoxybenzaldehydes were added to the medium at day 8 showed biotransformation of these compounds into chloro-3-fluoro-4-methoxy-benzaldehyde and chloro-3-bromo-4-methoxybenzaldehyde, respectively. No dichlorinated products were observed, suggesting that halogenation takes place only at the meta position on the 4-methoxybenzaldehydes. These experiments are the first to bring direct evidence of a halogenation mechanism, where the enzymatic attack takes place directly on the 4-methoxybenzaldehyde intermediates. © John Wiley & Sons, Inc.
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  • 3
    Electronic Resource
    Electronic Resource
    Hydrodynamic characteristics and gas-liquid mass transfer in a biofilm airlift suspension reactor (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 60 (1998), S. 627-635 
    Details
    ISSN: 0006-3592
    Keywords: airlift reactor ; biofilm ; hydrodynamics ; mass transfer ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The hydrodynamics and mass transfer, specifically the effects of gas velocity and the presence and type of solids on the gas hold-up and volumetric mass transfer coefficient, were studied on a lab-scale airlift reactor with internal draft tube. Basalt particles and biofilm-coated particles were used as solid phase. Three distinct flow regimes were observed with increasing gas flow rate. The influence of the solid phase on the hydrodynamics was a peculiar characteristic of the regimes. The volumetric mass transfer coefficient was found to decrease with increasing solid loading and particle size. This could be predominantly related to the influence that the solid has on gas hold-up. The ratio between gas hold-up and volumetric mass transfer coefficient was found to be independent of solid loading, size, or density, and it was proven that the presence of solids in airlift reactors lowers the number of gas bubbles without changing their size. To evaluate scale effects, experimental results were compared with theoretical and empirical models proposed for similar systems. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 627-635, 1998.
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  • 4
    Electronic Resource
    Electronic Resource
    Quantification of brewers' yeast flocculation in a stirred tank: Effect of physical parameters on flocculation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 190-200 
    Details
    ISSN: 0006-3592
    Keywords: flocculation ; brewers' yeast ; floc size ; single cells ; light extinction ; sedimentation ; stirred tank ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Quantification of yeast flocculation under defined conditions will help to understand the physical mechanisms of the flocculation process used in beer fermentation. Flocculation was quantified by measuring the size of yeast flocs and the number of single cells. For this purpose, a method to measure floc size and number of single cells in situ was developed. In this way, it was possible to quantify the actual flocculation during fermentation, without influencing flocculation. The effects of three physical parameters, floc strength, fluid shear, and yeast cell concentration, on flocculation during beer fermentation, were examined. Increasing floc strength results in larger flocs and lower numbers of single cells. If the fluid shear is increased, the size of the flocs decreases, and the number of single cells remains constant at approximately 10% of the total cells present. The cell concentration also influences flocculation, a reduction of 50% in cell concentration leads to a decrease of about 25% in floc size. The number of single cells decreases in linear proportion to the cell concentration. This means that, during yeast settling at full scale, the number of single cells decreases. The results of this study are used in a model for yeast flocculation. With respect to full scale fermentation the effect of cell concentration will play an important role, for flocculation and sedimentation will occur simultaneously leading to a quasi steady state between these phenomena. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 190-200, 1997.
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  • 5
    Electronic Resource
    Electronic Resource
    Modeling brewers' yeast flocculation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 330-341 
    Details
    ISSN: 0006-3592
    Keywords: brewers' yeast ; collision theory ; flocculation ; modeling ; surface erosion ; floc splitting ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Flocculation of yeast cells occurs during the fermentation of beer. Partway through the fermentation the cells become flocculent and start to form flocs. If the environmental conditions, such as medium composition and fluid velocities in the tank, are optimal, the flocs will grow in size large enough to settle. After settling of the main part of the yeast the green beer is left, containing only a small amount of yeast necessary for rest conversions during the next process step, the lagering. The physical process of flocculation is a dynamic equilibrium of floc formation and floc breakup resulting in a bimodal size distribution containing single cells and flocs.The floc size distribution and the single cell amount were measured under the different conditions that occur during full scale fermentation. Influences on flocculation such as floc strength, specific power input, and total number of yeast cells in suspension were studied. A flocculation model was developed, and the measured data used for validation. Yeast floc formation can be described with the collision theory assuming a constant collision efficiency. The breakup of flocs appears to occur mainly via two mechanisms, the splitting of flocs and the erosion of yeast cells from the floc surface. The splitting rate determines the average floc size and the erosion rate determines the number of single cells. Regarding the size of the flocs with respect to the scale of turbulence, only the viscous subrange needs to be considered. With the model, the floc size distribution and the number of single cells can be predicted at a certain point during the fermentation. For this, the bond strength between the cells, the fractal dimension of the yeast, the specific power input in the tank and the number of yeast cells that are in suspension in the tank have to be known. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 330-341, 1998.
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  • 6
    Electronic Resource
    Electronic Resource
    Modeling and measurements of fungal growth and morphology in submerged fermentations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 60 (1998), S. 216-229 
    Details
    ISSN: 0006-3592
    Keywords: model ; fungal fermentation ; morphology ; Aspergillus awamori ; agitation intensities ; dissolved oxygen tension ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Generalizing results from fungal fermentations is difficult due to their high sensitivity toward slight variation in starting conditions, poor reproducibility, and difference in strains. In this study a mathematical model is presented in which oxygen transfer, agitation intensity, dissolved oxygen tension, pellet size, formation of mycelia, the fraction of mycelia in the total biomass, carbohydrate source consumption, and biomass growth are taken into account. Two parameters were estimated from simulation, whereas all others are based on measurements or were taken from literature. Experimental data are obtained from the fermentations in both 2 L and 100 L fermentors at various conditions. Comparison of the simulation with experiments shows that the model can fairly well describe the time course of fungal growth (such as biomass and carbohydrate source concentrations) and fungal morphology (such as pellet size and the fraction of pellets in the total biomass). The model predicts that a stronger agitation intensity leads to a smaller pellet size and a lower fraction of pellets in the total biomass. At the same agitation intensity, pellet size is hardly affected by the dissolved oxygen tension, whereas the fraction of mycelia decreases slightly with an increase of the dissolved oxygen tension in the bulk. All of these are in line with observations at the corresponding conditions. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 216-229, 1998.
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of dissolved oxygen tension and mechanical forces on fungal morphology in submerged fermentation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 409-419 
    Details
    ISSN: 0006-3592
    Keywords: fungal morphology ; dissolved oxygen tension ; pellets ; agitation intensity ; stirred vessels ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effects of dissolved oxygen tension and mechanical forces on fungal morphology were both studied in the submerged fermentation of Aspergillus awamori. Pellet size, the hairy length of pellets, and the free filamentous mycelial fraction in the total biomass were found to be a function of the mechanical force intensity and to be independent of the dissolved oxygen tension provided that the dissolved oxygen tension was neither too low (5%) nor too high (330%). When the dissolved oxygen concentration was close to the saturation concentration corresponding to pure oxygen gas, A. awamori formed denser pellets and the free filamentous mycelial fraction was almost zero for a power input of about 1 W/kg. In the case of very low dissolved oxygen tension, the pellets were rather weak and fluffy so that they showed a very different appearance. The amount of biomass per pellet surface area appeared to be affected only by the dissolved oxygen tension and was proportional to the average dissolved oxygen tension to the power of 0.33. From this it was concluded that molecular diffusion was the dominant mechanism for oxygen transfer in the pellets and that convection and turbulent flow in the pellets were negligible in submerged fermentations. The biomass per wet pellet volume increased with the dissolved oxygen tension and decreased with the size of the pellets. This means that the smaller pellets formed under a higher dissolved oxygen tension had a higher intrinsic strength. Correspondingly, the porosity of the pellets was a function of the dissolved oxygen tension and the size of pellets. Within the studied range, the void fraction in the pellets was high and always much more than 50%. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 409-419, 1998.
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of plasma exposure on cultured hepatocytes: Implications for bioartificial liver support (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 51 (1996), S. 100-111 
    Details
    ISSN: 0006-3592
    Keywords: hepatocyte culture ; plasma ; free fatty acids ; bioartificial liver ; oxygen ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In order to examine their potential for use in a bioartificial liver, hepatocytes maintained in a collagen sandwich configuration were cultured for 9 days in heparinized rat plasma. The cells exhibited a progressive accumulation of cytoplasmic lipid droplets which proved to be mainly triglyceride (TG). The rate of TG accumulation correlated with the free fatty acid (FFA) content of the plasma. Removal of FFA and TG from plasma by ether extraction significantly reduced the rate and extent of TG accumulation. A smaller reduction in the rate and extent of TG accumulation was observed when cells were maintained in an oxygen enriched environment. The lipid accumulation suppressed urea synthesis, but clearance of the drug diazepam, although constitutively depressed in plasma, appeared unaffected by the accumulation. The functional and morphological effects of plasma exposure could be fully reversed after at least 6 days of plasma exposure by returning the cells to culture medium.The results indicate that elevated FFA in plasma induces lipid accumulation, which inhibits urea synthesis in cultured hepatocytes. This suggests that estimates of the cell number needed for effective liver support should not be based upon function measurements conducted in culture media. Furthermore, optimization of bioartificial liver support device use may have to be governed by the need to limit the plasma exposure of cultured hepatocytes. However, the highly responsive nature of these cultures and the reversibility of the plasma effects suggest that the collagen sandwich culture system is a promising foundation for the development of an effective bioartificial liver support system. © 1996 John Wiley & Sons, Inc.
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  • 9
    Electronic Resource
    Electronic Resource
    Physiological and chemical gradients in a Pseudomonas putida 54G biofilm degrading toluene in a flat plate vapor phase bioreactor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 361-371 
    Details
    ISSN: 0006-3592
    Keywords: biofilms ; bioremediation ; toluene ; vapor phase bioreactors ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A Pseudomonas putida 54G biofilm was grown on toluene vapor supplied as the sole external carbon and energy source in a flat plate biofilm reactor. Enumerations of cells in the biofilm were made using culture techniques (selective and nonselective for toluene) and microscopic techniques (total and respiring cells), and an analysis of the progression of the state of the culture was made by examination of various fractions of the populations. Long-term exposure to higher levels of toluene produced the following trends: (i) lower fraction of total cells that respired; (ii) lower fraction of culturable cells that also grew on toluene; (iii) higher fraction of respiring cells that could not grow on toluene plates; and (iv) a relatively constant fraction of total cells that could not be cultured on toluene. Respiration rate was determined using oxygen microsensors, and the fraction of the total respiration that was not associated with toluene uptake increased with higher toluene exposure. A combination of cryosectioning and respiration rate data was used to demonstrate that more respiring cells and a higher respiration rate both occurred at the base of the film, suggesting a deterioration in physiological state with continued exposure to toluene. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 361-371, 1997.
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