bluuebunny/crossref_metadata_2025_split huggingface dataset:
Purification of two immunologically distinct endoglucanases without affinity for microcrystalline cellulose from Cellulomonas sp. ATCC 21399
Authors: Poulsen O. M. , Petersen L. W. 
Published: May 2005

AbstractTwo endoglucanases (endoglucanase B and endoglucanase C) without affinity for cellulose were purified from the culture broth of Cellulomonas sp. ATCC 21399 using gelfiltration and ion exchange chromatography. Fused rocket immunoelectrophoresis was used to select the fractions with the highest content of endoglucanase and lowest content of contaminating proteins. The endoglucanases were purified to immunological homogeneity. In addition both endoglucanases were homogeneous when analyzed by sodium dodecyl sulfate—polyacrylamide gel electrophoresis (molecular weights of endoglucanase B and endoglucanase C were 67000 and 25000, respectively). Endoglucanase B was homogeneous when studied by isoelectric focusing showing one protein band at pl 4.3. Both endoglucanases lacked activity against microcrystalline cellulose (Avicel) and showed similar endo action on carboxymethylcellulose (CMC). Endoglucanase B had a high specific activity against CMC, H3PO4‐swollen Avicel and xylan, but showed no activity against galactomannan. In contrast, endoglucanase C showed activity against both CMC, xylan, and galactomannan all being polysaccharide substrates linked with β‐1‐4‐D‐glucoside bonds. The specific activity of endoglucanase C against H3PO4‐swollen Avicel was low.
Adaptive predictive control of a multistage fermentation process
Authors: Vigié P. , Goma G. , Renaud P. Y. , Chamilothoris G. , Dahhou B. , Pourciel J. B. 
Published: May 2005

AbstractTheoretical and experimental studies concerning the application of modern adaptive techniques for the control of continuous alcoholic fermentation of glucose by a yeast strain conducted in a multistage reactor are reported. The practical control objective was the regulation of the substrate concentration in the process effluent. Mathematical expressions for the control scheme are given, with the underlying control engineering argumentation. Suitable feeding of sugar for stage 2 was controlled to minimize the effluent sugar concentration.
Optimal temperature control for a structured model of plant cell culture
Authors: Bailey C. M. , Nicholson H. 
Published: May 2005

AbstractThis article calculates optimal open‐loop temperature trajectories that maximize the average rate of product synthesis of a plant cell culture. It uses a previously published five‐state mathematical model which describes the growth and product synthesis of a batch plant cell suspension culture of Catharanthus roseus under temperature control. The optimal open‐loop temperatures maximize the final product concentration for predefined fermentation periods. A single switch in temperature is shown by computer simulation to be near optimal, with a 22% increase in final product yield over that obtained at the optimal constant temperature. Examination of the achieved final product yield as a function of fermentation period allows this period also to be chosen optimally. This time is reduced from 16 days in the constant temperature case to 12 days in the switched temperature case.
Effect of operating parameters on specific production rate of a cloned‐gene product and performance of recombinant fermentation process
Authors: Park Sunghoon , Ryu Dewey D. Y. 
Published: May 2005

AbstractA two‐stage continuous system in combination with a temperature‐sensitive expression system were used as model systems to maximize the productivity of a cloned gene and minimize the problem associated with the plasmid instability for a high‐expression recombinant. In order to optimize the two‐stage fermentation process, the effects of such operational variables as temperature and dilution rate on productivity of cloned gene were studied using the model systems and a recombinant, Escherichia coli K12 ΔH1 Δtrp/pPLc23trp A1. When the expression of cloned gene is induced by raising the operating temperature above 38°C, a significant decrease in the colony‐forming‐units (CFU) of the plasmid‐harboring cell was observed, and the decrease was related to the product concentration. In order to describe this phenomenon, a new kinetic parameter related to the metabolic stress (metabolic stress factor) was introduced. It is defined as the ratio of the rate of change of pheno‐type from colony‐forming to non‐colony‐forming cells to the product accumulation per unit cell mass. At a fixed temperature of 40°C, the varying dilution rate D in the range of 0.35‐0.90 h−1 did not affect the metabolic stress factor significantly. At a fixed dilution rate of D = 0.35 h−1, this factor remained practically constant up to 41°C but increased rapidly beyond 41°C. The effects of temperature and dilution rate in the second stage on the specific production rate were also studied while maintaining the apparent specific growth rate (μ) of the second stage constant at or near μ = 0.26 h−1. Under a constant dilution rate, D2 = 0.35 h−1, the maximum specific production rate obtained was about qp, max = 38 units TrpA/mg cell/h at 41°C. At a constant temperature, T2 = 40°C, specific production rate increased with decreasing dilution rate with in the dilution rate range of D2 = 0.35‐0.90 h−1. Based on the results of our study, the optimal operating conditions found were dilution rate D2 = 0.35 h−1 and operating temperature T2 = 41°C at the apparent specific growth rate of 0.26 h−1. Under the optimal operating conditions, about threefold increase in productivity was achieved compared to the best batch culture result. In addition, the fermentation period could be extended for more than 100 h.
Cultivation of plant cells in a stirred vessel: Effect of impeller design
Authors: Hooker Brian S. , Lee James M. , An Gynheung 
Published: May 2005

AbstractSuspension cultures of Nicotiana tabacum were grown in a batch fermentor using different agitation systems. The effects of the impeller type, size, and agitation speed on the productivity of cell mass and secondary metabolites (phenolics) have been investigated. The use of a large, flat‐bladed impeller (diameter 7.6 cm; width 14.0 cm) improved culture growth significantly over systems using a regular, flat‐bladed impeller (diameter 5.6 cm; width 1.5 cm). An impeller of the same dimensions as the 14.0‐cm‐wide, large, flat‐bladed impeller with sail cloth blades yielded a higher maximum growth rate in the exponential phase but resulted in a longer lag phase. Overall (intracellular and extracellular) phenolics concentration showed a direct relationship to culture growth rate whereas extracellular concentrations were a function of agitation conditions. Power consumption and flow pattern studies were also completed to further characterize the different impellers tested.
On‐line optimization of biotechnological processes: I. Application to open algal pond
Authors: Guterman H. , Ben‐Yaakov S. 
Published: May 2005

AbstractA new on‐line optimization and control procedure applicable to biotechnological systems for which a precise mathematical model is unavailable has been developed and tested. The proposed approach is based on an online search for optimum operating conditions by an automatic system using a modified simplex algorithm to which several features have been added to permit real time operation. The simplex algorithm is the upper level of a hierarchical software package in which the other levels are cost evaluation, control, data acquisition, and signal processing. The optimization method was tested in a laboratory minipond for the cultivation of Spirulina platensis. The controlled parameters were light intensity, optical density, pH, and temperature. The proposed optimization method can be applied to other biological processes provided that the pertinent variables can be measured and controlled and the cost function can be defined mathematically.
Approximation of continuous fermentation by semicontinuous cultures
Authors: Westgate Paul J. , Emery Alden H. 
Published: May 2005

AbstractSemicontinuous fermentations, in which a fraction of a culture is replaced with fresh media at regular intervals, have been previously used as a means of approximating continuous growth. In most cases deviations from continuous operation were erroneously estimated using Fencl's model, which is only valid when the specific growth rate is independent of the substrate concentration. An approach to modeling Semicontinuous growth that incorporates the same kinetics followed in batch and continuous growth was developed and tested for Monod's expression for the specific growth rate. A dimensionless form of the model was used to simulate Semicontinuous fermentations for comparison to continuous growth. Differences between Semicontinuous and continuous growth were found to depend on three dimensionless variables: feed concentration, replacement rate, and time between replacements. For given values of the dimensionless feed concentration and time between replacements, a range of dimensionless replacement rates can be determined over which semi‐continuous cultures are approximately continuous.
A thermodynamic model to predict Phanerochaete chrysosporium INA‐12 adhesion to various solid carriers in relation to lignin peroxidase production
Authors: Asther Marcel , Bellon‐Fontaine Marie‐Noëlle , Capdevila Cécile , Corrieu Georges 
Published: May 2005

AbstractA thermodynamic model was used in this study to predict the adhesion of Phanerochaete chrysosporium INA‐12 as conidiospores or mycelium to various solid carriers. Theoretical predictions were closely reflected by experimental results. Amount of immobilized mycelium was higher for hydrophobic (polypropylene and polyurethane) than for hydrophilic carrier (stainless steel and grey). Lignin peroxidase production was stimulated in the same way. However, better results were obtained with polyurethane than with polypropylene and with grey than with stainless steel. These results were attributed to roughness effects of solid surfaces. Surface morphology characterization showed that the surface roughness parameter RA was higher for polyurethane and grey as compared to polypropylene and stainless steel, respectively. On the other hand, polyurethane is not simply rugous; it has an intraparticle porosity as well as a higher total surface area as compared to polypropylene.
Mathematical modeling of a single‐cell enzyme assay
Authors: Wittrup K. Dane , Bailey James E. 
Published: May 2005

AbstractA quantitative assay of β‐galactosidase activity in single cells of Saccharomyces cerevisiae has been developed using a fluorogenic substrate and flow cytometry [reported in Wittrup & Bailey, Cytometry, 9,394 (1988)]. The β‐galactosidase activity is expressed in yeast from the Escherichia coli lacZ gene under the control of the yeast GAL10 promoter, and is used as a marker for multicopy plasmid content. A nonfluorescent fluorogenic substrate is enzymatically cleaved by intracellular β‐galactosidase to form a fluorescent product. The accumulation of fluorescent product in single cells was found to depend on bulk substrate concentration and single‐cell enzyme activity in a fashion that could not be described by a Michaelis–Menten kinetic rate form. It has been demonstrated that diffusion limitation rather than enzyme activity can determine the level of single‐cell fluorescence under certain assay conditions, and a mathematical model has; been formulated which accounts for substrate and product diffusion. Guided by the mathematical model, the assay conditions were modified to allow measurement of single‐cell enzyme activity rather than diffusion rates.
Propagation of an amplifiable recombinant plasmid in Saccharomyces cerevisiae: flow cytometry studies and segregated modeling
Authors: Wittrup K. Dane , Bailey James E. , Ratzkin Barry , Patel Avantika 
Published: May 2005

AbstractEfficient expression of a foreign protein product by the yeastSaccharomyces cerevisiaerequires a stable recombinant vector present at a high number of copies per cell. A conditional centromere yeast plasmid was constructed which can be amplified to high copy number by a process of unequal partitioning at cell division, followed by selection for increased copy number. However, in the absence of selection pressure for plasmid amplification, copy number rapidly drops from 25 plasmids/cell to 6 plasmids/cell in less than 10 generations of growth. Copy number subsequently decreases from 6 plasmids/cell to 2 plasmids/cell over a span of 50 generations. A combination of flow cytometric measurement of copy number distributions and segregated mathematical modeling were applied to test the predictions of a conceptual model of conditional centromereplasmid propagation. Measured distributions of plasmid content displayed a significant subpopulation of cells with a copy number of 4–6, evenin a population whose mean copy number was 13.5. This type of copy number distribution was reproduced by a mathematical model which assumes that amaximum of 4‐6 centromere plasmids per cell can be stably partitionedat cell division. The model also reproduces the observed biphasic kinetics of plasmid number instability. The agreement between simulation and experimental results provides support for the proposed model and demonstrates the utility of the flow cytometry/segregated modeling approach for the study of multicopy recombinant vector propagation.
Oxygen transfer enhancement in aqueous/perfluorocarbon fermentation systems: II. theoretical analysis
Authors: Junker Beth H. , Wang Daniel I. C. , Hatton T. Alan 
Published: May 2005

AbstractTwo theoretical approaches were examined to quantify observed experimental oxygen transfer enhancements in aqueous/perfluorocarbon (pfc) fermentation systems. Steady‐state macroscopic balance results indicated that enhancements in the presence of reaction were a function of the gas bubble‐to‐droplet diameter ratio for pfc‐in‐water dispersions, but primarily a function of only the droplet diameter for water‐in‐pfc dispersions. The problem of unsteady‐state diffusion into a semi‐infinite composite medium was employed to predict enhancements in the absence of reaction based on the relative permeabilities of the perfluorocarbon and water phases. Since potential enhancements exceeded actual enhancements in the presence of an oxygen consuming reaction for water‐in‐pfc dispersions, the use of less expensive, lower oxygenpermeable oil phases is recommended in practice.
Critical assessment of the steady‐state Na2SO3 feeding method for kla measurement in fermentors
Authors: Linek V. , Beneš P. , Sinkule J. 
Published: May 2005

AbstractImportant aspects of kla measurement in agitated aerated vessels are briefly characterized from the standpoint of reliability of the measured data. It seems that most of the kla data, based on a number of variants of the steady‐state and dynamic methods in noncoalescent liquids, do not have a clear physical meaning, because they are affected by the differences between the actual driving force and the driving force assumed by the model used for its evaluation. A reliability test is given for the Na2SO3 feeding steady‐state method (FSM), by comparing the results of air and pure oxygen absorption in a noncoalescent liquid (0.5M Na2SO4 solution) with the results obtained by the independent pressure step dynamic method (RDM). The RDM is one of a few variants of the dynamic method which gives correct kla data unaffected by nonideal mixing of the gas phase in the reactor. It was found that the FSM yields correct kla values only when pure oxygen is used for absorption. When air is absorbed, the FSM gives kla values in the region of kla > 0.1 s−1 substantially (to 55%) lower than those for pure oxygen absorption.
Esterification reactions of lipase in reverse micelles
Authors: Hayes Douglas G. , Gulari Erdogan 
Published: May 2005

AbstractThe activities of lipase from Candida cylindracea and Rhizopus delemar have been investigated in water/AOT/iso‐octane reverse micellar media through the use of two esterification reactions: fatty acid‐alcohol esterification and glyceride synthesis. Such media promotes the occurrence of these two lipase‐catalyzed reactions due to its low water content. The effect of various parameters on the activity of lipase from C. cylindracea in reverse micelles was determined and compared to results where alternate media were employed. It was observed that the structure of the media, as dictated by the type and concentration of the substrates and products and by the water/AOT ratio, w0, had a strong impact on enzyme activity. Strong deactivation of both typase types occurred in reverse micelles, especially in the absence of substrates and for w0 values greater than 3.0. Glyceride synthesis was realized with lipase from R. delemar, but not with that from C. cylindracea; the temperature and concentration of substrates and water strongly dictated the reaction rate and the percent conversion.
Inhibition of Trichoderma reesei cellulase by sugars and solvents
Authors: Holtzapple Mark , Cognata Mona , Shu Yuancai , Hendrickson Christie 
Published: May 2005

AbstractInhibition of Trichoderma reesei cellulase by sugars (glucose, δ‐gluconolactone, and cellobiose) and solvents (ethanol, butanol, and acetone) was studied using cellulose azure. Glucose, cellobiose, ethanol, and butanol were noncompetitive inhibitors, δ‐gluconolactone was a mixed inhibitor, and acetone was a noncompetitive activator. Converting cellobiose to glucose reduces the effective inhibitor binding constant by 6 times and converting cellobiose to ethanol reduces it by 16 times.
Prediction of the profiles of the elution bands of proteins in preparative liquid chromatography
Authors: Katti Anita , Huang Jun‐Xiong , Guiochon Georges 
Published: May 2005

AbstractA semiequilibrium model of chromatography has been developed to account for the elution profile of high concentration bands. The use of this model requires the prior determination of the equilibrium isotherms of the studied compounds in the chromatographic phase system. The model is applied here to a study of the isocratic elution bands of chicken albumin and conalbumin on a weak anion exchanger in aqueous buffered solutions. Satisfactory agreement is observed between the experimental elution profiles of large‐sample‐size bands of chicken albumin and conalbumin.
Chitin/chitosan transformation by thermo‐mechano‐chemical treatment including characterization by enzymatic depolymerization
Authors: Pelletier A. , Lemire I. , Sygusch J. , Chornet E. , Overend R. P. 
Published: May 2005

AbstractChitosan, the deacetylated derivative of chitin, was until recently produced by hydrolysis in 50% (w/v) NaOH. Application of thermo‐mechano‐chemical technology to chitin deacetylation was evaluated as an alternative method of chitosan production. This process consists of a cascade reactor unit operating under reduced alkaline conditions of 10% (w/v) NaOH. Prior mercerization of chitin at 4°C for 24 h was required for high deacetylation yields. Sudden decompression of the aqueous alkaline suspension of mercerized chitin resulted in near complete deacetylation of chitin. Reactor residence time was 90 s at 230°C prior to decompression. The chitosan produced was characterized by elemental analysis, 13C–NMR and enzymatic depolymerization. Enzymatic determination of the degree of acetylation of chitin/chitosan mixtures was also investigated. Relative chitinase and/or chitosanase digestibilities were shown to be strongly dependent on chitin deacetylation. Based on enzymatic digestibilities, the alkaline aqueous high shear process does not appear to produce significant secondary products. Correlation of chitosanase digestibility with percentage of deacetylation provides a simple biological assay to study chitosan composition.
Partitioning of host and recombinant cells in aqueous two‐phase polymer systems
Authors: LaMarca Concetta , Lenhoff Abraham M. , Dhurjati Prasad 
Published: May 2005

AbstractThe separation of host and recombinant Escherichia coli bacterial cells has been studied using the surface‐sensitive technique of partitioning in aqueous two‐phase polymer systems. Experiments were designed to probe charge‐and hydrophobicity‐related property differences of antibiotic‐resistant recombinant cells and their antibiotic‐sensitive hosts. Differential partitioning was observed in both charge‐sensitive and non‐charge‐sensitive phase systems for three host–recombinant cell systems, but the non‐charge‐related effects appear to have a greater impact on partitioning behavior. This result suggests that plasmid‐encoded products related to antibiotic resistance modify the surface hydrophobicity of the E. coli bacterial cell and that these differences can be exploited for cell separation.
Effect of cell growth rate on the performance of a two‐stage continuous culture system in a recombinant Escherichia coli fermentation
Authors: Park Sunghoon , Ryu Dewey D. Y. , Kim Jeong Yoon 
Published: May 2005

AbstractAs part of the process optimization of a two‐stage continuous culture system, the effect of growth rate μ on the performance of the second stage (production stage) was studied in a recombinant Escherichia coli K12 (ΔH1Δtrp/pPLc23trpA1). Important parameters considered were specific gene expression rate, plasmid content, and plasmid stability, all of which were closely related to the cell growth rate and the production rate of the cloned gene product (trpα). When operating conditions were maintained constant (T1 = 35°C, D1 = 0.9 h−1, T2 = 40°C, and D2 = 0.7 h−1) and μ was varied, plasmid content in the second stage showed its maximum at μ = 0.4 h−1 and decreased thereafter. Specific gene expression rate linearly increased with increasing μ, while plasmid stability decreased. Optimum cell growth rate giving the maximum value in overall productivity was observed at around μ = 0.4 h−1. The contribution or role of the three parameters, specific gene expression rate, plasmid content, and plasmid stability in exhibiting the maximum productivity at the optimal μ is discussed.
Trypsin purification by affinity binding to small unilamellar liposomes
Authors: Powers Johnny D. , Kilpatrick Peter K. , Carbonell Ruben G. 
Published: May 2005

AbstractA novel protein purification process using affinity‐ligand‐modified liposomes and membrane ultrafiltration is described. The feasibility of the process was tested using trypsin as the model protein and p‐aminobenzamidine (PAB) as the affinity ligand for trypsin. The affinity liposomes were prepared by covalently attaching PAB to the surface of small unilamellar liposomes via the hydrophilic spacer arm diglycolic acid. The liposomes were comprised of dimyristoyl phosphatidyl choline, cholesterol, and dimyristoyl phosphatidyl ethanolamine to which the diglycolic acid was attached. The equilibrium binding constant between trypsin and immobilized PAB was shown to be dependent on the PAB density of the liposome surface. Bound trypsin was eluted from the liposomes by the trypsin inhibitor benzamidine. Trypsin was purified from a trypsin/chymotrypsin mixture and from one of its naturally occurring sources, porcine pancreatic extract. A recovery yield from the crude mixture of 68% was obtained with a trypsin purity of 98%. The affinity‐modified liposomes were stable in the complex mixture and retained their trypsin binding capacity after multiple adsorption/elution cycles over a 30‐day period.