bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow Cytometry and Cell Cycle Kinetics in Continuous and Fed‐Batch Fermentations of Budding Yeast
Authors: Alberghina L. , Ranzi B. M. , Porro D. , Martegani E. 
Published: March 2005

AbstractCell size distributions, obtained either as protein distribution by flow cytometry or as cell volume distribution by a Coulter counter, give relevant information about the growth conditions of populations of budding yeast Saccharomyces cerevisiae. We have previously found a good correlation between these distributions and the growth rate in continuous cultures (Ranzi et al., Biotechnol. Bioeng. 1986, 28, 185–190). We now present determinations of the protein distributions and cell volume distributions during different fed‐batch fermentations performed with a simple on/off controller. Since during the fed‐batch fermentation a true steady state is not obtained, the distributions continuously change with time, but nevertheless we observed a good correlation between the average of both distributions and the actual growth rate. The behavior of the cell size distributions can be interpreted on the basis of a two‐threshold cell cycle model in which both the critical protein content at budding (Ps) and the critical protein content for cell division (Pm) are differently modulated by the growth rate. Additional findings will be presented showing that this model can be used to successfully explain the insurgence and the maintenance of oscillatory states in continuous cultures.
In Vivo NMR Analysis of the Influence of Pyruvate Decarboxylase and Alcohol Dehydrogenase of Zymomonas mobilis on the Anaerobic Metabolism of Escherichia coli
Authors: Ricci Juan C. Diaz , Hitzmann Bernd , Bailey James E. 
Published: March 2005

AbstractPhosphorus‐31 NMR studies of Escherichia coli expressing cloned pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adh) genes from Zymomonas mobilis revealed significant changes in the concentration of intracellular metabolites. The intracellular concentrations of phosphate, sugar phosphates, NAD(H), NTP, NDP, and UDPG of the strain HB101 expressing pdc, adh, or both genes were analyzed at quasi steady state during the anaerobic catabolism of glucose. The evolution of the intracellular pH and extracellular pH during glucose consumption showed a constant value of ΔpH equal to 0.2 pH unit that did not depend on the expression of the Zymomonas genes. The strains expressing PDC only exhibited greatest changes in intracellular composition with significantly decreased inorganic phosphate, NAD(H), NTP, and UDPG and significantly increased sugar phosphates. Analysis of the fermentation products during the NMR experiments provided further information about the physilogical changes observed in the cells. Two plasmid effects on the host metabolism are reported, one induced by the plasmid utilized as control (pUCl9), and the other induced by the expression of the pet operon. In both cases an enhancement of the glucose uptake rate was observed. Although the plasmid carrying adh induces a rapid metabolic inhibition, the expression of pdc does not. The expression of pdc and adh together showed a physiological enhancement that is attributable not to effects on external pH but rather to the effect of the switch in pathways from mixed acid to ethanol fermentation.
Up‐Flow Attached‐Bed Bioreactor for Continuous Ethanol Fermentation
Authors: Chen Hung‐Chang 
Published: March 2005

AbstractEthanol fermentation was carried out in an up‐flow attached‐bed (UFAB) continuous fermentor using different microorganisms, substrates, and attachment supports. When Saccharomyces fragilis was attached to cellulose acetate to ferment deproteinized and concentrated acid whey, ethanol productivity as high as 6.9 g/(L.h), 10 times that of a batch reactor, was obtained in a continuous UFAB bioreactor. When Zymomonas mobilis was attached to vermiculite in a continuous UFAB bioreactor to ferment a 10% glucose feed, ethanol productivity as high as 105.7 g/(L.h) was achieved with a dilution rate of 3.6 h−1 and an ethanol concentration of 29.0 g/L.
Block Copolymer Microdomains: A Novel Medium for Enzymatic Reactions
Authors: Gupte A. , Nagarajan R. , Kilara A. 
Published: March 2005

AbstractBlock copolymers exhibit the phenomenon of microdomain formation in pure states as well as in solutions. The microdomains vest the block copolymer assemblies with the intriguing characteristics of microheterogeneous media. We demonstrate that this microheterogeneity in hydrophobic‐hydrophilic block copolymer systems can be exploited for immobilizing enzymes and to carry out enzymatic reactions. Examples involving cholesterol oxidase and horseradish peroxidase are provided here. The observed changes in the enzymatic activity in block copolymer microdomains from that in the aqueous media are interpreted in terms of the hydrophobicity of the reaction microenvironment. The block copolymer microdomains are simple to generate, well defined, and easily reproducible. Therefore, they hold significant potential as media for enzymatic biosynthetic reactions when the substrates or the reaction products are water insoluble.
Kinetic Model for Substrate Utilization and Methane Production in the Anaerobic Digestion of Organic Feeds
Authors: Barthakur Archana , Bora Munindra , Singh H. Devendra 
Published: March 2005

AbstractA kinetic model for anaerobic digestion of organic substrates is presented. Two complementary kinetic equations, one each for substrate utilization and methane production, are derived. The model equations take into account extracellular hydrolysis of complex substrates and consider the hydrolyzed products as the limiting substrates for cell growth and product formation according to Monod kinetics. The equations are applied to the experimental data on the anaerobic digestion of a variety of feeds reported in the literature with reasonable agreement of the predicted and observed values. When substrate hydrolysis is poor and rate limiting, the equations are reduced to a Contoistype equation. On the other hand, if no hydrolysis of the substrate is involved as in the case of simple and soluble substrate, the equations take the form of a Monod‐type relationship. Thus, the equations represent a generalized kinetic expression for fermentation relating the Monod and Contois equations, which hold good in two extreme cases.
Production and Deactivation of Biosurfactant by Bacillus licheniformis JF‐2
Authors: Lin Sung‐Chyr , Sharma Mukul M. , Georgiou George 
Published: March 2005

AbstractBacillus licheniformis JF‐2 produces a lipopeptide surfactant with excellent interfacial properties (Lin et al., 1990, 1992). An HPLC assay was developed to monitor the concentration of the lipopeptide in the fermentation broth and was employed to determine the effect of the composition of the growth medium on biosurfactant production. A maximum concentration of 110 mg/L lipopeptide was obtained in optimized media with 1.0% (w/v) glucose as the carbon source. The maximum amount of surfactant was obtained in early stationary‐phase cultures, but subsequently decreased rapidly and disappeared completely from the fermentation broth within 8 h. It was shown that the surfactant is chemically stable in the culture supernatant but becomes internalized by stationary‐phase cells. The apparent rate of surfactant internalization was not inhibited by carbonyl cyanide (m‐chlorophenyl) hydrazone (CCCP), an uncoupler of oxidative phosphorylation, suggesting that it is not dependent on the availability of ATP and/or a charged membrane. A variety of physical and chemical treatments failed to release the surfactant from the cells. In minimal media the rate of surfactant internalization could be reduced by optimizing the concentration of phosphate and by increasing the amount of magnesium, whereas the nitrogen source, calcium, and trace salts had no effect. Since a related lipopeptide has been shown to be responsible for DNA transformation competence in certain Bacillus subtilis strains, it is possible that the internalization of the B. licheniformis JF‐2 surfactant may be a developmentally important process related to the ability of the cells to take up extraneous DNA.
Stochastic Simulation of 2μ Multicopy Plasmid Amplification in Yeast
Authors: Shaw Mark R. , Schiek Richard , Wittrup K. Dane 
Published: March 2005

AbstractThe 2μ plasmid of Saccharomyces cerevisiae has been used extensively as a vector for foreign protein expression because of its natural amplification to 60–100 copies per cell. The amplification of the 2μ plasmid occurs through a recombinational mechanism which we have simulated using two free parameters: the FLP recombinase DNA‐binding probability and FLP specific enzymatic activity. Model results indicate that a single plasmid amplifies to 5.5–7 copies on average at maximal FLP concentrations and that amplification is approximately proportional to the probability of FLP attachment but independent of its specific enzymatic activity. Thus, FLP overexpression should lead to maximal plasmid amplification. The model predicts the existence of topologically novel replication intermediates.
Biomass Estimation in Plant Cell Cultures Using an Extended Kalman Filter
Authors: Albiol Joan , Robusté Jordi , Casas Carles , Poch Manel 
Published: March 2005

AbstractUse of carbohydrate concentration measurements linked to a digital filter was studied for biomass estimation in plant cell cultures. Due to the high complexity of the biological system, the strategy followed has been to work with a simple model and to rely on the filter to adapt the values of the model parameters to changes in the system behavior. Results obtained with this approach have shown the method to be efficient for biomass estimation, both in Erlenmeyer flasks and in bioreactors with changing operational conditions.
An Extended Model for Open‐Ended Fluorosensor Probes
Authors: Ladén Gunnar , Niklasson Claes 
Published: March 2005

AbstractMeasurements on pure solutions of NADH (8–800 μM) were made at different path lengths (0–140 mm) with an open‐ended fluorosensor. It was shown that a geometric factor must be included in a model to quantitatively explain the results. A mathematical expression for this factor was found, and parameter estimations were made. It was shown that the often‐used implicit assumption of a completely directed emitted light is not correct, A better fit was obtained by assuming the emitted light to be uniformly distributed in all directions. However, it was necessary to consider the slight divergence of the excitation light beams in the model.
Low‐Temperature Transitions in Fresh and Osmotically Dehydrated Plant Materials
Authors: Anglea Stacey A. , Karathanos Vaios , Karel Marcus 
Published: March 2005

AbstractPhase transitions in several plant materials were studied using differential scanning calorimetry (DSC) and small oscillatory amplitude rheology. The glass transition temperature of the unfrozen phase, recrystallization peak of water, and melting point of ice, in fresh plant materials as well as in samples osmotically dehydrated in 15, 30, and 45% sucrose solutions, were identified using both thermal and mechanical analysis. Mechanical analysis showed that the glass transition temperature of the unfrozen phase was approximately ‐45°C for fresh and osmotically dehydrated plant materials at all concentrations. Thermal analysis showed that the glass transition of the unfrozen phase in osmotically dehydrated potato samples varied depending on the amount of freeze‐concentration achieved.
Characterization of Water Distribution in Cell Pellets Using Nonlabeled Sodium Thiosulfate as an Interstitial Space Marker
Authors: Larroche Christian , Besson Isabelle , Dussap Claude‐Gilles , Bourrust Francois , Gros Jean‐Bernard 
Published: March 2005

AbstractA procedure for determination of the intracellular water content of cells using a single, nonlabeled solute as an interstitial space marker is proposed. Sodium thiosulfate, which can be accurately assayed by a tritrimetric method, is found to be a good compound for this purpose. Cells are recovered both by filtration and centrifugation; the two techniques gave the same value for internal water, i.e., 650 mg of H2O/g of wet matter for Corynebacterium melassecola and 390 mg of H2O/g of wet matter for Penicillium roquefortii spores. The methodology of data handling, based on a regression technique, is also described. It allows one to obtain very reliable results and should be useful for any marker.
Advances in Metabolic Control Analysis
Authors: Liao James C. , Delgado Javier 
Published: March 2005

AbstractA methodology for characterizing metabolic systems using the response, control, and elasticity coefficients has emerged since the early 1970s. This methodology, termed metabolic control analysis, aims to characterize the sensitivity of metabolic responses with respect to changes in enzyme activities or parameters without the use of full mathematical models. It takes advantage of several relationships among the coefficients at the steady state. These relationships facilitate the experimental determination of the coefficients and serve as a consistency test when the coefficients are determined independently. Both the theoretical and experimental aspects of this analysis are reviewed, with an emphasis on recent developments and issues commonly discussed in the literature.
Effect of Chelatants on Gellan Gel Rheological Properties and Setting Temperature for Immobilization of Living Bifidobacteria
Authors: Camelin I. , Lacroix C. , Paquin C. , Prévost H. , Cachon R. , Divies C. 
Published: March 2005

AbstractThe effect of various concentrations of sequestrants (sodium citrate, sodium meta‐phosphate, and BDTA) was studied on gellan gel (1.5–2.5% (w/v)) setting temperature and rheological properties. Addition of EDTA between 0 and 0.8% (w/v) led to a progressive decrease of setting temperature. Citrate and metaphosphate decreased this parameter when added up to 0.4 or 0.6%, depending on gellan gum concentration, eventually resulting in the absence of gel formation at room temperature for the 1.5% gellan solution containing 0.4% citrate. This effect was accompanied by a significant decrease of gel strength and stiffness and might be attributed to the binding of the divalent cations required for chain association during gelation by chelatants. With the aim of lowering the gel setting temperature during the cell entrapment process while maintaining high mechanical properties, a gel made of 2.5% gellan gum and 0.2% sodium citrate was used to entrap Bifidobacterium longum ATCC15707. Ions and pH of the inoculum during the immobilization step influenced the long‐term mechanical stability of the gel beads during continuous fermentation in a stirred tank reactor. High stability as well as high biocatalyst activity was obtained when a washed cell suspension was used as the inoculum. Gellan gel produced by dissolving gellan gum in a sodium citrate solution may be a promising entrapment matrix for temperature‐sensitive cells such as mesophilic lactic acid bacteria and eukaryotic cells.
Fractional Factorial Study of Hybridoma Behavior. 1. Kinetics of Growth and Antibody Production
Authors: Gaertner John G. , Dhurjati Prasad 
Published: March 2005

AbstractA comprehensive approach was taken toward the quantitative study of hybridoma growth and antibody production. A fractional factorial experimental method was used to identify important variables and variable interactions affecting hybridoma behavior. The variables studied include temperature, pH, dissolved oxygen, glucose, glutamine, base medium, serum, lactate, and ammonium. The growth rate was strongly affected by the levels of dissolved oxygen, pH, temperature, and base medium. Interactions between temperature, pH, and dissolved oxygen were important. The optimal pH for growth depends upon the temperature and dissolved oxygen concentration. In general, growth was fastest at low dissolved oxygen levels. The growth rate was very sensitive to low concentrations of base medium, but was relatively insensitive to the serum concentration at levels above 2.5%. Antibody production was stimulated by high concentrations of base medium and serum and inhibited by ammonium and lactate. Antibody production increased linearly with serum concentration. In general, conditions that favored a high growth rate also favored a high specific rate of antibody production. The functional dependencies of antibody production on base medium and ammonium were similar to those for cell growth; however, antibody production and cell growth exhibited different dependencies on serum. Mathematical descriptions of cell growth and antibody production were developed. These experimental results have significant implications for the optimization of hybridoma growth in bioreactors.
A Computer Model for Intracellular pH Regulation in Chinese Hamster Ovary Cells
Authors: Wu P. , Ray N. G. , Shuler M. L. 
Published: March 2005

AbstractA single‐cell model for Chinese hamster ovary (CHO) cells has been extended to study the regulation of intracellular pH. This model provides for the first time a direct mechanistic linkage between intracellular pH control and cellular metabolism. Among the known mechanisms that regulate and disturb pHi, the Na/H antiport, effect of lactate and ammonia, proton leakage, and external pH have been included in the model. The ability of the model to predict both steady‐state and transient pHi has been tested against experimental studies. The “regular model” that has been used to predict cell growth in suspension and batch cultures can predict the steady‐state pHi and the transient response of pHi to an alkaline load well, but it had to be modified in terms of the maximum activity of the Na/H antiport in order to simulate the transient response of pHi to an acid load. The modification indicates the possibility that a cell could activate the Na/H antiport under acute acid load but return to its basal level of Na/H antiport activity under steady‐state conditions, even when the cell interior is under low‐pH conditions (6.7–7.0).
Application of Oxygen Microbubbles for in Situ Biodegradation of p‐Xylene‐Contaminated Groundwater in a Soil Column
Authors: Jenkins Kristen B. , Michelsen Donald L. , Novak John T. 
Published: March 2005

AbstractIn situ biodegradation of p‐xylene was studied in a 7‐cm (2.75‐in.) soil column using oxygen microbubbles to supply the electron acceptor. Pseudomonas putida continuously degraded p‐xylene below detectable limits until the oxygen supply was exhausted. Retention time in the biodegradation zone was approximately 45 min. Vent losses claimed 5–10% of the injected oxygen, with 71–82 % being utilized. The pressure drops resulting from increased biomass showed a slight increase over the first few days followed by a gradual decline, indicating that the biomass will not plug the soil matrix under the conditions of this test. The addition of ferrous iron in the feed and its subsequent oxidation to ferric hydroxide did not affect biodegradation, nor did it cause appreciable soil plugging. In order to precipitate the ferrous iron before it reached the microbubbles, an air‐sparging section was added. This resulted in volatilization of p‐xylene with very little ferrous oxidation until the groundwater reached the oxygen microbubbles.
5‐Aminolevulinic Acid: A Potential Herbicide/Insecticide from Microorganisms
Authors: Sasikala Ch. , Ramana Ch. V. , Rao P. Raghuveer 
Published: March 2005

Abstract5‐Aminolevulinic acid (ALA), an intermediate of the biological tetrapyrrole synthesis, can be used as a photodynamic herbicide/insecticide. Among the various microorganisms capable of its production, anoxygenic phototrophic bacteria produce ALA in considerable amounts, making it worthwhile to work toward commercial exploitation. Knowledge of the biochemical synthesis of ALA and its physiological and genetic regulation in microorganisms can enable the biotechnologist to manipulate them for enhancing ALA production for possible practical applications.
Optimal Experimental Design for Parameter Estimation in Unstructured Growth Models
Authors: Baltes M. , Schneider R. , Sturm C. , Reuss M. 
Published: March 2005

AbstractA method of optimal experimental design for parameter estimation in unstructured growth models is presented. The approach is based on a method suggested by Munack (1991) for application in fed‐batch processes. In a critical analysis of this method, special emphasis is given to the model validity, because unstructured growth models often are not valid under transient conditions. In consequence, a combined object function has been introduced, which considers model validity and the accuracy of the kinetic parameters to be estimated. The application of this method for fed‐batch processes leads to satisfactory results. Investigations of different fed‐batch strategies regarding model validity and the quality of parameter estimation are presented. In addition, an experimental verification has been performed with fermentations of the yeast Trichosporon cutaneum.
Three‐Dimensional Mammalian Cell Growth on Nonwoven Polyester Fabric Disks
Authors: Petti Stacy A. , Lages Ana C. , Sussman Martin V. 
Published: March 2005

AbstractSmall disks of nonwoven polyester fabric (NWPF), similar to Fibra‐Cel carriers, were surface treated with strong acid and used as a high surface area support matrix for in vitro culture of anchorage dependent MRC‐5 cells. The disks can be autoclaved, and require inocula concentrations of only 2–5% of the final cell densities, which have reached 108 cells/mL of disk bed volume. Scanning electron microscopy photographs shown herein reveal that cells grow in a multilayered fashion between the randomly arrayed fibers of the nonwoven fabric, emulating in vivo growth.
Cost Analysis of Ethanol Production from Willow Using Recombinant Escherichia coli
Authors: Sivers Margareta Von , Zacchi Guido , Olsson Lisbeth , Hahn‐Hügerdal Bärbel 
Published: March 2005

AbstractThis study comprises a technical and economic analysis of the production of fuel ethanol by fermentation of a pentose‐rich hydrolysate with recombinant Escherichia coli, strain KO11. Hydrolysate from steam‐pretreated willow was used as raw material in calculations regarding the fermentation. The calculations were based on a feed capacity of 10 metric tons of dry willow per hour to the pretreatment stage, providing 35 metric tons of hydrolysate per hour, consisting of 45 g of sugars/L, to the pentose fermentation plant. A detoxification step was included, since the hydrolysate has been shown to have an inhibitory effect on the E. coli KO11. The technical data used in the calculations were based on a kinetic fermentation model, which was developed from laboratory‐scale experiments in a previous study. The economic analysis predicted an ethanol production cost of 48¢/L in the pentose fermentation plant, indicating potentially good economy. The detoxification cost constitutes 22% of this cost. Sensitivity analyses revealed that if the concentration of sugars in the feed to the fermentation was decreased by 40% to 27 g/L, the ethanol production cost was increased to 54 ¢/L. The production cost was increased to 50 ¢/L ethanol if the cell mass was recirculated to the fermentation stage 5 times instead of 20.