摘要:

AbstractEleven experimental investigation of diffusion in gels containing immobilized cells are reviewed. The experimental data, which quantitatively express the diffusion coefficient as a function of the cell concentration, are compared with a number of well‐known equations developed for mass transfer in heterogeneous media. Based on this comparison, a procedure for the theoretical prediction of effective diffusion coefficients in cell‐containing gels is recommen

ISSN:0006-3592    

DOI:10.1002/bit.260380502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractEnergy balance calculations were performed for different physiological states during batch growth ofSaccharomyces cerevisiaewith glucose as carbon and energy source. For the different physiological states, energy recoveries close to one were obtained, which permitted a continuous control that the constantly changing growth process was quantified accurately. During the respiro‐fermantative phase of growth, during which glucose served as the carbon and energy source, a low‐heat‐yield value (ΔQx) of −8.6 kJ/g dry biomass formed was obtained. This low‐heat‐yield value was due to the mainly fermentative metabolism during the middle of this phase of growth. After a transition phase, the ethanol produced during the respiro‐fermentative growth was respired. During this respiratory phase, the heat yield values increased markedly, resulting in a lowest value of −42.7 kJ/g. The low‐heat‐yield values of the respiro‐fermentative growth is not a reflection of the most efficient metabolism ofS. cerevisiae. On the contrary, during the middle of this phase, 74% of the energy input was dissipated as ethanol, 6% was dissipated as heat, and the energy conserved as biomass was just 13%, while during the early respiratory phase, 69% of the energy input was dissipated as heat, and 22% of the energy input was conserved as biomass. By mathematical modeling and direct monitoring on‐line of the rate of heat production, continuous calculations of (1) glucose consumption, and (3) biomass production were performed, and were shown to correlate closely with measured values for the continuously

ISSN:0006-3592    

DOI:10.1002/bit.260380503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe report the development of new class of discrete models that can accurately describe the contact‐inhibited proliferation of anchorage‐dependent cells. The models are based on cellular automata, and they quantitatively account for contact inhibition phenomena occurring during all stages of the proliferation process: (a) the initial stage of “exponential” growth of cells without contact inhibition; (b) the second stage where cell colonies form and grow with few colony mergings; and (c) the final stage where proliferation rates are dominated by colony merging events. Model prediction are presented and analyzed to study the complicated dynamics of large cell populations and determine how the initial spatial cell distribution, the seeding density, and the geometry of the growth surface affect the observed proliferation rates. Finally, we present a model variant that can simulate contact‐inhibited proliferation of asynchronous cell populations with arbitrary cell cycle–time distribution. The latter model can also compute the percentage of cells that are in a specific phase of their division cycle at a

ISSN:0006-3592    

DOI:10.1002/bit.260380504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThis study establishes that the cellular automata models developed in an earlier article capture the essential features of the proliferation process for anchorage‐dependent contact‐inhibited cells. Model predictions are in excellent agreement with experimental data obtained with bovine pulmonary artery endothelial cells. The models are particularly suitable for predictive purposes since they have no adjustable parameters. All model parameters can be easily obtained from a priori measurements. Our studies also show that proliferation rates are very sensitive to the spatial distributions of seed cells. The adverse effects of seeding heterogeneities become more pronounced as a cell population approaches confluency and they should be accounted for in experimental studies attempting to assess the response of cells to external stim

ISSN:0006-3592    

DOI:10.1002/bit.260380505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe ΔH f0unit weight of a complex substance such as a biological macromolecule is almost always obtained by means of combustion analysis. In theory, this can also be done by summing the ΔH f0values for the monomers comprising the macromolecule plus the enthalpic energies involved in their polymerization. The enthalpy of formation of one unit‐carbon formula weight of driedEscherichia coliK‐12 cells was determined by summing the values of the enthalpies of formation of the quantities of monomers in the major classes of macromolecules substances comprising the cellular biomass and the enthalpic energies involved in their polymerizations. To this value was added the enthalpy of formation of the cellular ions in their aqueous standard states, per unit‐carbon formula weight of cellular substance and the enthalpy change with respect to the ionization of the protein amino acid side chains. If it is assumed that the cellular fabric is insoluble and that the ions are soluble, the sum of the enthalpies of formation of all the cellular components should closely approximate the enthalpy of formation of one unit‐carbon formula weight equivalent of living cells. Using this value, a calculation of the enthalpy change accompanying anabolism shows this latter to be effectively zero, indicating that the heat of growth (anabolism plus catabolism) is equal to that calculated for catabolism alone. This conclusion is in accord with those of several investigators who have used manometry or direc

ISSN:0006-3592    

DOI:10.1002/bit.260380506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe capacities of yeast wild‐type and mutants strains known to lack specific ADH isoenzymes to produceL‐phenylacetyl carbinol (PAC) and benzyl alcohol in biotransformation trials were also investigated. Pyruvate decarboxylase activity, responsible for PAC formation and ADH activity, which can participate in reduction of benzaldehyde to benzyl alcohol, was also determined in each strain. In addition, the capacity of each strain to produce ethanol was investigated. Mutant strains lacking all of the isoenzymes, ADH‐I, ADH‐II, and ADH‐III, still exhibited some ADH activity and were capable of production of benzyl alcohol an

ISSN:0006-3592    

DOI:10.1002/bit.260380507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractBed fluidization offers the possibility of gaining the advantages of fixed‐film biological processes without the disadvantage of pore clogging. However, the biofilm detachment rate, due to hydrodynamics and particle‐to‐particle attrition, is very poorly understood for fluidized‐bed biofilm processes. In this work, a two‐phase fluidized‐bed biofilm was operated under a constant surface loading (0.09 mg total organic carbon/cm2day) and with a range of bed height (H), fluid velocities (U), and support‐particle concentrations (Cp). Direct measurements were made for the specific biofilm loss rate coefficient (bs)and the total biofilm accumulation (XfLf). A hydrodynamic model allowed independent determination of the biofilm density (Xf), biofilm thickness (Lf), liquid shear stress (τ), and Reynolds number (Re). Multiple regression analysis of the results showed that increased particle‐to‐particle attrition, proportional toCpand increased turbulence, described by Re, caused the biofilms to be denser and thinner. The specific detachment rate coefficient (bs) increased asCpand Re increased. Almost all of the 6, values were larger than predicted by a previous model derived for smooth biofilms on a nonfluidized surface. Therefore, the turbulence and attrition of bed fluidization appear to be dominant det

ISSN:0006-3592    

DOI:10.1002/bit.260380508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractGlycerol‐fatty acid esterification has been conducted with lipase fromR. delemarin water/AOT/isooctane reverse micellar media, with the major product being 1‐monoglyceride, a useful food‐emulsifier. 1,3‐diglyceride was also synthesized, but to a much lesser extent. For a given set of initial conditions, the reaction productivity, measured in terms of the initial product formation rate,V0, and the final or equilibrium concentration of product, is optimal for a particular concentration of each surfactant, fatty acid, glycerol, and water. Many of these optimal values correlate well with a “critical” region on the phase diagram. Also, results indicate lipase‐catalyzed esterification stops due to the achievement of kinetic equilibrium expect for a few cases where enzyme deactivation is severe. Dynamic light scattering was employed to examine the influence of water, glycerol, and fatty acid on micellar and interfacial structure. Results from this technique indicate enzyme kinetic are linked to interfacial phenomena and the presence of substrates at the inter

ISSN:0006-3592    

DOI:10.1002/bit.260380509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAn integrated solvent (ABE) fermentation and product removal process was investigated. A stable solvent productivity of 3.5 g/L h was achieved by using cells ofClostridium acetobutylicumimmobilized onto a packed bed of bonechar, coupled with continuous product removal by pervaporation. Using a concentrated feed solution containing lactose at 130g/L, a lactose value of 97.9% was observed. The integrated fermentation and product removal system, with recycling of the treated fermentor effluent containing only low amount of solvents (/but lactose and acids), leads to only low acid losses. Therefore, most of the acids are converted to solvents, and this results in a high solvent yield of 0.39 g solvents/g lactose utilized. The pervaporation system provided a high product removal rate even at low solvent concentrations. A solvent membrane flux of 7.1 g/m2h with a selectivity of 5 was achieved during these investigations. The system proved to be very reliable.

ISSN:0006-3592    

DOI:10.1002/bit.260380510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractUltrafiltration of high‐purity grade bovine serum albumin has been carried out under various temperature between 5 and 30°C and at various cross‐flow velocities, pressures, and concentrations with the aim of studying protein denaturation and its consequences on the process. Three different pump heads have been tested. Denaturation of proteins in solution has been monitored by laser light scattering and size exclusion chromatography. The rate of protein denaturation increases with temperature, cross‐flow, and time. It is observed that membrane fouling is different whether denaturation has occurred or not. Under high‐concentration polarization, denaturation can occur in the boundary layer if the wall concentration exceeds 400 g/L. It is shown how the residence time, operating temperature, and pressure play an important part in membrane fouling. This can provide guidelines for process design and

ISSN:0006-3592    

DOI:10.1002/bit.260380511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY