bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhancement effect of polyethylene glycol on enzymatic synthesis of cephalexin
Authors: Hyun Chang K. , Choi Joon H. , Kim Jung H. , Ryu Dewey D. Y. 
Published: December 2004

AbstractIn an enzymatic synthesis of cephalexin (CEX) using an acylase from Xanthomonas citri, the effect of polyethylene glycol (PEG) on the synthetic reaction of 7‐amino‐3‐deacetoxycephalosporanic acid (7‐ADCA) and D‐alpha‐phenyl‐glycine methyl ester (PGM) to CEX was investigated. The addition of PEG (MW 300–20,000) increased the yield significantly. This yield enhancement effect tended to increase with the increasing molecular weight of PEG. Addition of PEG to the reaction system did not affect both the CEX and PGM hydrolytic reactions. The PEG added to the reaction medium used in these experiments did not depress the water activity significantly, and the product yield improvement could not be explained by the activity alone. The PEG stabilized the enzyme activity to some extent, but this stabilizing effect was only partially attributable to the yield enhancement of CEX. The enhancing effect of PEG on the synthetic yield increased with the increasing PEG molecular weight or the length of the poly(oxy‐1,2‐ethanediyl) chain, which increases the hydrophobicity of PEG. This finding consequently has led to the conclusion that the PEG structure renders the affinity between enzyme and 7‐ADCA, which is a hydrophobic substrate. The microenvironmental hydrophobicity of PEG and its interaction with the hydrophobic substrate was found to be the main reason for the improvement of the CEX yield. In fact, the Michaelis–Menten kinetic constant for 7‐ADCA, K7‐ADCA in the presence of PEG was smaller than that in the control system (without PEG addition). © 1993 John Wiley & Sons, Inc.
Cell retention culture with an internal filter module: Continuous ethanol fermentation
Authors: Chang Ho Nam , Lee Woo Gi , Kim Beom Soo 
Published: December 2004

AbstractA new internal filter feedback system with a stainless steel filter was introduced and its application for continuous ethanol fermentation was investigated. The filter performance was highly influenced by agitation speed and yeast concentration. Retention coefficient with a filter of 2 μm pore size was found more than 97.5%, and the filter was suitable for yeast separation. Maximum yeast concentration was 157 g/L and the best operable cell concentration was between 90 and 150 g/L. Which was similar to that obtained in the external membrane cell recycle culture. The cell concentration in the fermentor was maintained by manipulation of dilution rate and bleed ratio with the growth rate. The internal filter feedback system was successfully operated for more than 10 days. This study shows that the internal filter feedback system with a stainless steel filter can be used high‐density cell culture and ethanol fermentation. Furthermore, it can be scaled up more easily than the external cell recycle system. © 1993 John Wiley & Sons, Inc.
A simulation model for the continuous production of acetoin and butanediol using Bacillus subtilis with integrated pervaporation separation
Authors: Dettwiler B. , Dunn I. J. , Heinzle E. , Prenosil J. E. 
Published: December 2004

AbstractThe potential for producing acetoin and butanediol with a Bacillus subtilis strain was investigated with continuous culture using molasses as carbon substrate. The steady‐state results were influenced by both oxygen and undetermined limiting compounds. Employing the known metabolic pathways, four overall stoichiometry relations were used with an energetic assumption on the energy requirements for biomass formation to establish a linear relations were used with an energetic assumption on the energy requirements for biomass formation to establish a linear relation between the overall rates, whose parameters were determined by linear regression. This provided a relationship for the product formation rate. The chemostat culture data were described with a growth kinetics model, which included limitation by molasses and oxygen as well as diauxic effects and product inhibition. The biokinetics model was combined with an experimentally verified model for the membrane Pervaporation. From this combined model were determined the influence of the membrane characteristics (enrichment factors and membrane area) and the dilution rate on the performance of the integrated process. Simulations revealed that an increase of the enrichment factor, possible by membrane improvement, would have counteracting influences, owing to decreased product inhibition but with lower biomass concentration. © 1993 Wiley & Sons, Inc.
Enhancement of cloned gene product synthesis via autoselection in recombinant Saccharomyces cerevisiae
Authors: Napp Scott J. , Da Silva Nancy A. 
Published: December 2004

AbstractSaccharomyces cerevisiae autoselection strains with mutations in the ura3, fur1, and urid‐k genes have been obtained through a sequential isolation procedure. This autoselection system is an extension of one described by Loison et al. The mutations effectively block both the pyrimidine biosynthetic and salvage pathways and in combination are lethal to the host. Therefore, a plasmidencoded URA3 gene is essential for cell viability regardless of the growth conditions, and complex (traditionally nonselective) media can be employed without the risk of plasmid loss. The effects of medium enrichment on growth and cloned gene product synthesis were examined in batch culture for two autoselection strains. The plasmid gene product β‐galactosidase was under the control of the yeast GAL1 promoter, and two methods of induction were employed; one strain was induced via temperature shift while the other was induced by galactose addition. Three nutrient media were investigated: a lean selective medium (SD), a richer semidefined medium (SDC), and a rich complex medium (YPD). The results demonstrated the improvements in cloned gene productivity possible when the growth medium is enriched, with up to 10‐fold increases in β‐galactosidase productivity observed. Plasmid instability and mutation reversion were not problems for the autoselection strains, even in uracil‐containing medium. Short‐term plasmid stabilities were approximately 90% in all three media tested. During continuous culture of the autoselection temperature‐sensitive strain, long‐term plasmid stability was excellent and β‐galactosidase expression remained high after more than 25 residence times under inducing conditions. In contrast, both β‐galactosidase specific activity and plasmid stability decreased linearly with time for an analogous nonautoselection strain. The introduced fur1 and uridk mutations were very stable; after more than 50 generations of growth in complex medium, stability values of 99–100% were measured. © 1993 Wiley & Sons, Inc.
Fluid‐mechanical forces in agitated bioreactors reduce the CD13 and CD33 surface protein content of HL60 cells
Authors: Lakhotia Sanjay , Bauer Kenneth D. , Papoutsakis Eleftherios T. 
Published: December 2004

AbstractFlow cytometry was used to examine the effect of hydrodynamic forces in surface aerated stirred tank bioreactors on the quantity of CD13 and CD33 surface proteins of Hl60 (human promyelocytic leukemia) cells. A step increase in agitation of the 2‐L bioreactors from 80 to 400 rpm reduced the apparent growth rate and the average CD13 and CD33 content per HL60 cell. The effects on the two surface proteins were observed within 30‐60 min following the increase in the agitation and preceded observed effects on cell growth by at least 10 h. Upon reduction of the agitation rate back to 80 rpm, the CD13 and CD33 content recovered (in ca. 10 h) for CD13 and ca. 29h for (CD33) to the levels of the control culture whose agitation rate was maintained at 80rpm. The CD13 and CD33 cell content was reduced even at agitation rates (270 rpm) that did not affect cell proliferation. Pluronic F68 (a commonly used shear protectant) had a protective effect on the CD33 content per cell of cultures subjected to hydrodynamic injury but no effect on the CD13 cell content. Possible bioprocessing and physiological implications of these findings are discussed © 1993 Wiley & Sons, Inc.
Diffusion and reaction within porous packing media: A phenomenological model
Authors: Jones Warren L. , Dockery Jack D. , Vogel Curtis R. , Sturman Paul J. 
Published: December 2004

AbstractA phenomenological model has been developed to describe biomass distribution and substrate depletion in porous diatomaceous earth (DE) pellets colonized by Pseudomonas aeruginosa. The essential features of the model are diffusion, attachment and detachment to/from pore walls of the biomass, diffusion of substrate within the pellet, and external mass transfer of both substrate and biomass in the bulk fluid of a packed bed containing the pellets. A bench‐scale reactor filled with DE pellets was inoculated with P. aeruginosa and operated in plug flow without recycle using a feed containing glucose as the limiting nutrient. Steady‐state effluent glucose concentrations were measured at various residence times, and biomass distribution within the pellet was measured at the lowest residence time. In the model, microorganism/substrate kinetics and mass transfer characteristics were predicted from the literature. Only the attachment and detachment parameters were treated as unknowns, and were determined by fitting biomass distribution data within the pellets to the mathematical model. The rate‐limiting step in substrate conversion was determined to be internal mass transfer resistance; external mass transfer resistance and microbial kinetic limitations were found to be nearly negligible. Only the outer 5% of the pellets contributed to substrate conversion. © 1993 Wiley & Sons, Inc.
Determining metabolic sensitivity coefficients directly from experimental data
Authors: Schlosser Paul M. , Holcomb Tyler , Bailey James E. 
Published: December 2004

AbstractThe application of metabolic control theory (MCT), or other methods of determining metabolic sensitivity to the rates of specific cellular processes, such as enzymatic reactions, requires knowledge of the elasticity coefficients (system partial derivatives) for the processes under study. Although rate equations are available in the literature for some enzymatic reactions, there are many reactions and processes for which this is not the case. Although one could perform the experiments necessary to determine the rate equations for a given system, these equations are, in fact, not required for the calculation of sensitivities–only the elasticities (the derivatives) are needed. A more direct and efficient approach would be to compute elasticities directly from experimental data. Errors can analysis and alternative regression techniques are presented which not only allow one to eliminate data components with excessive noise, but also provide guidance as to what additional data may be require for accurate sensitivity analysis. This information indicates which measurements require more accuracy and what additional experiments should be conducted to reduce errors in calculated metabolic sensitivity coefficients. © 1993 Wiley & Sons, Inc.
Separation albumin–PEG: Transmission of PEG through ultrafiltration membranes
Authors: Lentsch Sandrine , Aimar Pierre , Orozco Jose Luis 
Published: December 2004

AbstractTransmission of polyethylene glycol (PEG) through ultrafiltration membranes has been studied under various operating conditions of pressure, crossflow, and concentration, using different membranes cut‐offs and two module designs with the aim of understanding the separation of PEG from BSA. The influence of protein adsorption and fouling of the choice of a membrane has also been considered. Retention depends in general on the molecule to average pore size ratio, as expected, but also on concentration polarization. Accordingly, all operating and design parameters favoring concentration polarization lead to higher transmission. At high fluxes, flexible macromolecules can pass through the membrane, even if the random coil is larger than the apparent average pore. From a process selectivity point of view, the best way to separate PEG from BSA would be to use a membrane totally retaining BSA and to enhance concentration polarization of PEG. Unfortunately, such conditions also increase fouling and concentration polarization by BSA, which limits flux and thus PEG concentration polarization and transmission. Consequences of such conditions on separation efficiency are discussed. © 1993 Wiley & Sons, Inc.
A novel BOD sensor based on bacterial luminescence
Authors: Hyun Chang‐Kee , Tamiya Eiichi , Takeuchi Toshifumi , Karube Isao , Inoue Noriuki 
Published: December 2004

AbstractA reagent‐type BOD sensor with a new principle employing a luminous bacterium, Photobacterium phosphoreum, was developed. The increased intensity of luminescence resulting from the cellular assimilation of organic compounds in wastewater was detected by a photodiode. The BOD response of the bacterial reagent could be obtained within 15 min with ±7% error. The temperature condition for optimal BOD response was 18° to 25°C at pH 7 to 8, indicating that it is possible to measure BOD at room temperature without having to stabilize the temperature of the measuring system. For practical use, two procedures for long‐term preservation of the bacterial reagent, vacuum drying method and freezing method, are suggested. The metabolic characteristics of employed luminous bacteria were investigated by comparing the BOD values for several pure organic substrates estimated by the BOD sensor with conventional 5‐day BOD values. In comparison with the 5‐day measurement for some wastewater samples, BOD values estimated by the sensor showed comparatively good agreement with those measured by the 5‐day method. © 1993 Wiley & Sons, Inc.
Symmetric branching model for the kinetics of mycelial growth
Authors: Viniegra‐González G. , Saucedo‐Castañeda G. , López‐Isunza F. , Favela‐Torres E. 
Published: December 2004

AbstractA mathematical model, linking microscopic to macroscopic parameters of the kinetics of mycelial growth is presented. The model consists of two parts: (a) a microscopic description, based on the assumption that growth of a mycelium can be represented approximately by the growth of a symmetric binary tree, where the branching level (microscopic state variable) is logarithmically related to the number of tips and segments; and (b) a macroscopic description which makes use of the microscopic description in order to define the parameters related to the evolution of biomass (macroscopic state variable) as a function of time. The latter uses a distribution of arrested tips in a population of mycelia, in order to estimate the fraction of non‐growing biomass in terms of a power law function with coefficient, n, of the biomass concentration. The microscopic description explains the fact that the germ tube specific growth rate of Aspergillus nidulans measured in a growth chamber, is about the double the specific growth rate of this organism, when measured in shake flasks. It predicts that the length of the hyphal growth unit of the mycelium of Geotrichum candidum would be approximately the double the germ tube length measured at the time just before the first branching event. It also allows the derivation of useful expressions for predicting macroscopic parameters, such as the maximal specific growth rate, the initial amount of biomass, and the amount of biomass before the branching process starts. Those estimates are done in terms of microscopic quantities, i.e., the amount of germinated spores, the diameters of the spores and hyphae, the average rate of tip extension, and the average internodal segment length. Estimation of coefficient n by fitting the macroscopic description to a growth curve of A. niger gives an indication on the degree of skewness of the distribution of arrested mycelia. Estimated macroscopic parameters are in relative good agreement with measured average segment length. © 1993 John Wiley & Sons, Inc.
Biochemical production capabilities of escherichia coli
Authors: Varma Amit , Boesch Brian W. , Palsson Bernhard O. 
Published: December 2004

AbstractMicrobial metabolism provides at mechanism for the conversion of substrates into useful biochemicals. Utilization of microbes in industrial processes requires a modification of their natural metabolism in order to increase the efficiency of the desired conversion. Redirection of metabolic fluxes forms the basis of the newly defined field of metabolic engineering. In this study we use a flux balance based approach to study the biosynthesis of the 20 amino acids and 4 nucleotides as biochemical products. These amino acids and nucleotides are primary products of biosynthesis as well as important industrial products and precursors for the production of other biochemicals. The biosynthetic reactions of the bacterium Escherichia coli have been formulated into a metabolic network, and growth has been defined as a balanced drain on the metabolite pools corresponding to the cellular composition. Theoretical limits on the conversion of glucose, glycerol, and acetate substrates to biomass as well as the biochemical products have been computed. The substrate that results in the maximal carbon conversion to a particular product is identified. Criteria have been developed to identify metabolic constraints in the optimal solutions. The constraints of stoichiometry, energy, and redox have been determined in the conversions of glucose, glycerol, and acetate substrates into the biochemicals. Flux distributions corresponding to the maximal production of the biochemicals are presented. The goals of metabolic engineering are the optimal redirection of fluxes from generating biomass toward producing the desired biochemical. Optimal biomass generation is shown to decrease in a piecewise linear manner with increasing product formation. In some cases, synergy is observed between biochemical production and growth, leading to an increased overall carbon conversion. Balanced growth and product formation are important in a bioprocess, particularly for nonsecreted products. © 1993 John Wiley & Sons, Inc.
Improved protein synthesis and secretion through medium enrichment in a stable recombinant yeast strain
Authors: Wang Zhengjun , Da Silva Nancy A. 
Published: December 2004

AbstractTwo Saccharomyces cerevisiae strains were employed to investigate the effects of medium enrichment on the expression and secretion of a recombinant protein. One was a stable autoselection strain with mutations in the ura3, fur1, and urid‐k genes. The combination of these three mutations blocks both the pyrimidine nucleotide biosynthetic and salvage pathways and is lethal to the cells. Retention of the plasmid, which carries a URA3 gene, was essential for cell viability. Therefore, all media were selective, allowing cultivation of the strain in complex medium. The second strain was a nonautoselection (control) strain and is isogenic to the first except for the fur1 and urid‐k mutations. The plasmid utilized contains the yeast invertase gene under the control of the MFα1 promoter and leader sequence. The expression and secretion of invertase for the autoselection strain were examined in batch culture for three media: a minimal medium (SD), a semidefined medium (SDC), and a rich complex medium (YPD). Biomass yields and invertase productivity (volumetric activity) increased with the complexity of the medium; total invertase volumetric activity in YPD was 100% higher than in SDC and 180% higher than in SD. Specific activity, however, was lowest in the SDC medium. Secretion efficiency was extremely high in all three media; for the majority of the culture, 80–90% of the invertase was secreted into the periplasmic space and/or culture medium. A glucose pulse at the end of batch culture in YPD facilitated the transport of residual cytoplasmic invertase. For the nonautoselection strain, invertase productivity did not improve as the medium was enriched from SDC to YPD, and plasmid stability in the complex YPD medium dropped from 54% to 34% during one batch fermentation. During long‐term sequential batch culture in YPD, invertase activity decreased by 90% and the plasmid‐containing fraction dropped from 56% to 8.8% over 44 generations of growth. The expression level for the autoselection strain, however, remained high and constant over this time period, and no reversion at the fur1 or urid‐k locus was observed. © 1993 John Wiley & Sons, Inc.
Loss of antibody productivity is highly reproducible in multiple hybridoma subclones
Authors: Merritt Steven E. , Palsson Bernhard O. 
Published: December 2004

AbstractAn immunoglobulin G (IgG2b) producing hybridoma cell line (S3H5/γ2bA2) was cloned and subcloned. Twenty subclones were grown in parallel while being adapted in a stepwise fashion to serum‐free medium. Following adaptation to serum‐free medium, it was found that 16 of the 20 subclones remained at a relatively constant proportion of nonproducing cells. Three of the remaining subclones transiently deviated from this balance but eventually returned toward this population composition. One subclone continued to lose productivity. A population balance was reached at approximately 8% of the population being nonproducers. The loss of antibody productivity was thus highly reproducible. © 1993 John Wiley & Sons, Inc.
Activated sludge process performance using a multistage tower aeration tank
Authors: Shimizu Tatsuo , Kudo Kenzo , Nasu Yoshikazu 
Published: December 2004

AbstractThis study's objective was to clarify both experimentally and theoretically whether a vertical multistage tower aeration tank system is advantageous as compared with a completely mixed system, particularly with respect to purification efficiency, sludge settleability, and excess sludge production. In comparing the two systems: (1) purification efficiency in the multistage tower aeration system with partial fluid mixing with a large Peclet number was higher than in a corresponding completely mixed system for all applied organic loadings; (2) the multistage tower aeration system had some definite advantages with respect to sludge settleability and excess sludge production; (3) the activated sludge system's higher performance with partial fluid mixing was shown quantitatively with the axial dispersion model in conjunction with growth kinetics which involved rapid uptake such as biosorption and subsequent oxidative biodegradation processes of organic substances. © 1993 John Wiley & Sons, Inc.
Production of tPA in recombinant CHO cells under oxygen‐limited conditions
Authors: Lin Andy A. , Kimura Roy , Miller William M. 
Published: December 2004

AbstractAnimal cell bioreactors are often limited by the oxygen supply. The reduction in oxygen consumption per cell that occurs under hypoxic conditions may be exploited as a method for increasing reactor capacity if additional glucose is provided to offset increased glycolytic activity. The effects of oxygen deprivation on recombinant tPA (tissue‐type plasminogen activator) production were investigated using midexponential and slowly growing CHO cells. The specific oxygen consumption rate can be reduced by at least 50% (mild hypoxic conditions) without affecting the cell growth rate, maximum cell concentration, tPA production rate, or tPA quality (as characterized by the tPA‐specific activity and SDS‐PAGE analysis). This suggests that mild‐hypoxic conditions (with sufficient glucose) can be used to double the cell concentration and volumetric tPA production rate (at a constant volumetric oxygen supply rate) without sacrificing product quality. However, anoxic conditions should be avoided. When slowly growing cultures were exposed to anoxia, the tPA production rate decreased by 80% without affecting tPA quality. However, when midexponential cultures were exposed to anoxia, the drop in tPA production was accompanied by a decrease in tPA quality that ranged from a 40% decrease in tPA specific activity to extensive tPA degradation. © 1993 John Wiley & Sons, Inc.