bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved penicillin amidase production using a genetically engineered mutant of Escherichia coli ATCC 11105
Authors: Robas N. , Zouheiry H. , Branlant G. , Branlant C. 
Published: December 2004

AbstractPenicillin G amidase (PGA) is a key enzyme for the industrial production of penicillin G derivatives used in therapeutics. Escherichia coli ATCC 11105 is the more commonly used strain for PGA production. To improve enzyme yield, we constructed various recombinant E. coli HB101 and ATCC 11105 strains. For each strain, PGA production was determined for various concentrations of glucose and phenylacetic and (PAA) in the medium. The E. coli strain, G271, was identified as the best performer (800 U NIPAB/L). This strain was obtained as follows: an E. coli ATCC 11105 mutant (E. coli G133) was first selected based on a low negative effect of glucose on PGA production. This mutant was then transformed with a pBR322 derivative containing the PGA gene. Various experiments were made to try to understand the reason for the high productivity of E. coli G271. The host strain, E. coli G133, was found to be mutated in one (or more) gene(s) whose product(s) act(s) in trans on the PGA gene expression. Its growth is not inhibited by high glucose concentration in the medium. Interestingly, whereas glucose still exerts some negative effect on the PGA production by E. coli G133, PGA production by its transformant (E. coli G271) is stimulated by glucose. The reason for this stimulation is discussed. Transformation of E. coli G133 with a pBR322 derivative containing the Hindlll fragment of the PGA gene, showed that the performance of E. coli G271 depends both upon the host strain properties and the plasmid structure. Study of the production by the less efficient E. coli HB101 derivatives brought some light on the mechanism of regulation of the PGA gene. © 1993 John Wiley & Sons, Inc.
Intensification of mass transfer in aqueous two‐phase systems
Authors: Save Sanjiv V. , Pangarkar Vishwas G. , Kumar S. Vasanth 
Published: December 2004

AbstractA novel technique which intensifies conventional aqueous two‐phase extraction by conversion of dispersed phase into colloidal gas aphrons (CGAs) has been developed for extraction of an enzyme. In the present work, amyloglucosidase (1,4‐α‐D‐glucan glucohydrolase) was extracted using a polyethylene glycol‐sodium sulfate‐water system. The lighter phase, i.e., polyethylene glycol (PEG) rich phase, was converted into CGAs which were then dispersed into a salt rich phase. The effect of type of surfactant and its concentration, dispersed phase velocity, phase composition, and type of sparger on the dispersed phase mass transfer coefficient was investigated. The results suggests 9–16 times higher values of mass transfer coefficient compared to spray column. The multiorifice sparger at concentrations of 0.33 g/L of cetyl trimethyl ammonium chloride yielded best results. © 1993 John Wiley & Sons, Inc.
Cell–cell adhesion and aggregation: Influence on the growth behavior of CHO cells
Authors: Renner W. A. , Jordan M. , Eppenberger H. M. , Leist C. 
Published: December 2004

AbstractThe influence of cell‐cell adhesion on the growth behavior of Chinese hamster ovary (CHO) cells in suspension culture was investigated. CHO cells form aggregates under suboptimal growth conditions. Clusters are formed around decaying and dead cells. The deoxyribonucleic acid (DNA) released from these cells was found to mediate the cells was found to mediate the cell‐cell adhesion. Cluster formation dramatically influenced the growth behavior of the cells. First, cells within aggregates showed a strongly reduced specific proliferation rate, and second, shear forces exerted on large aggregates caused a considerable higher specific death rate than those exerted on single cells. These factors led to a reduction of the specific growth rate up to 50%. This decrease could be avoided by addition of DNase 1 to the medium. It is shown that the separate determination of the specific proliferation and death rates is not feasible with state‐of‐the‐art methods. To achieve a more profound and precise description of the growth pattern of animal cells, we propose an extended Monod model and describe the relevant methods. © 1993 John Wiley & Sons, Inc.
Evaluation of a hepatocyte‐entrapment hollow fiber bioreactor: A potential bioartificial liver
Authors: Nyberg Scott L. , Shatford Russel A. , Peshwa Madhusudan V. , White James G. , Cerra Frank B. , Hu Wei‐Shou 
Published: December 2004

AbstractWe have developed a hepatocyte entrapment hollow fiber bioreactor for potential use as a bioartificial liver. Hepatocytes were entrapped in collagen gel inside the lumen of the hollow fibers. Medium was perfused through the intraluminal region after contraction of the hepatocyte‐entrapment gel. Another medium stream, comparable to the patient's blood during clinical application, passed through the extracapillary space. Viability of hepatocytes remained high after 5 days as judged by the rate of oxygen uptake and viability staining. Urea and albumin synthetic activities were also sustained. Transmission electron microscopic examination demonstrated normal ultrastructural integrity of hepatocytes in such a bioreactor. With its sort‐term, extracorporeal support of acute liver failure, the current bioreactor warrants further investigation. © 1993 John Wiley & Sons, Inc.
Immobilization of lipase for effective interesterification of fats and oils in organic solvent
Authors: Cho Sang‐Woo , Rhee Joon Shick 
Published: December 2004

AbstractIn order to investigate quantitatively the interesterification reaction, triolein and stearic acid were used as substrates and eight commercially available lipases were tested for their suitability for the reaction. Three fungal lipase preparations were found to be suitable. The hydrolytic activity of the commercial lipases was tested with olive oil, and it 2was noted that there was no correlation between their hydrolytic and interesterification activities. Among the lipases tested, Mucor miehei lipase was chosen for further study because of it high protein content and its relatively high hydrolytic and interesterification activities, both of which are required for effective interesterification. The effect of water activity of the interesterification reaction was investigated. interesterification activity was shown to be maximum at the water activity of 0.25. As the water activity of the lipase increased, hydrolysis of triglyceride was accelerated. At zero water activity, high conversion was achieved, although interesterification activity was relatively lower than that at the water activity of 0.25. A new and simple immobilization method was developed in order to render hydrophobicity to the lipase and hence to improve the interesterification activity of the lipase. The lipase was immobilized covalently with glutaraldehyde or with six alkyl chains as spacers onto Florisil (magnesium silicate, a inorganic matrix). Interesterification activity of the immobilized lipase with the hydrophobic spacers were increased against that of re lipase. The increase of activity was up to 8‐fold that of the original activity of free lipase when the spacer was 7‐aminoheptanoic acids. Relatively high stability of the immobilized lipase was shown in a continuous packed bed column reactor with a half‐life of 97 days. © 1993 John Wiley & Sons, Inc.
Reverse micelles in protein separation: The use of silica for the back‐transfer process
Authors: Leser Martin E. , Mrkoci Kristina , Luisi Pier Luigi 
Published: December 2004

AbstractIn order to use reverse micellar solutions successfully for the separation of proteins, good methods are needed to recover the biomolecules into an aqueous environment after solubilization into organic micellar media. Usually the recovery is accomplished by equilibrating the protein‐loaded reverse micellar solution with a water phase containing an appropriate salt (back‐transfer). In this article we describe an alternative “back extraction” procedure which is based on the addition of silica to the protein‐containing reverse micellar solution. In this way, the water is stripped from the reverse micellar solution. [i.e., bis(2‐ethylhexyl) sodium sulfosuccinate (AOT)/isooctane/water] and the proteins adsorb to the silica particles. The adsorption process is shown to be practically quantitative. The subsequent recovery of the proteins form the silica into an aqueous solution turns out to be most efficient at alkaline pH (pH 8); 60–80 of the total protein (α‐chymotrypsin or trypsin) could be recovered. The specific enzyme activity at the end of the whole cycle can be as high as 80−100%. The procedure is applied also for the back extraction from micellar solutions in which, instead of AOT, a biocompatible surfactant such as a synthetic short‐chain lecithin was used. It is shown that the recovery of a α‐chymotrypsin and trypsin is also achievable under these conditions in quite good yield and under good maintenance of the enzyme's catalytic activity. © 1993 John Wiley & Sons, Inc.
Fuzzy control of ethanol concentration its application to maximum glutathione production in yeast fed‐batch culture
Authors: Alfafara Catalino G. , Miura Keigo , Shimizu Hiroshi , Shioya Suteaki , Suga Ken‐ichi , Suzuki Kazuyuki 
Published: December 2004

AbstractA fuzzy logic controller (FLC) for the control of ethanol concentration was developed and utilized to realize the maximum production of glutathione (GSH) in yeast fedbatch culture. A conventional fuzzy controller, which uses the control error and its rate of change in the premise part of the linguistic rules, worked well when the initial error of ethanol concentration was small. However, when the initial error was large, controller overreaction resulted in an overshoot.An improved fuzzy controller was obtained to avoid controller overreaction by diagnostic determination of “glucose emergency states” (i.e., glucose accumulation or deficiency), and then appropriate emergency control action was obtained by the use of weight coefficients and modification of linguistic rules to decrease the overreaction of the controller when the fermentation was in the emergency state. The improved fuzzy controller was able to control a constant ethanol concentration under conditions of large initial error.The improved fuzzy control system was used in the GSH production phase of the optimal operation to indirectly control the specific growth rate μ to its critical value μc. In the GSH production phase of the fed‐batch culture, the optimal solution was to control μ to μc in order to maintain a maximum specific GSH production rate. The value of μc also coincided with the critical specific growth rate at which no ethanol formation occurs. Therefore, the control of μ to μc could be done indirectly by maintaining a constant ethanol concentration, that is, zero net ethanol formation, through proper manipulation of the glucose feed rate. Maximum production of GSH was realized using the developed FLC; maximum production was a consequence of the substrate feeding strategy and cysteine addition, and the FLC was a simple way to realize the strategy. © 1993 John Wiley & Sons, Inc.
Continuous measurement of microbial heat production in laboratory fermentors
Authors: van Kleeff B. H. A. , Kuenen J. G. , Heijnen J. J. 
Published: December 2004

AbstractThe possibility of continuously measuring the heat produced by microorganisms in an ordinary laboratory fermentor was studies. An inventory of the heat flows influencing the temperature of the culture was made. The magnitude and standard deviation in these heat flows were studied from theoretical and practical viewpoints. Calibration procedures were tested, and a model describing the heat flows in steady state and during dynamic conditions was made. Microbial heat production could be calculated accurately with the help of this model, appropriate temperature measurements, and equipment properties measured during the calibration procedures. It was found that the measurement of heat production could be done with an accuracy similar to that in the O2 uptake measurement. © 1993 John Wiley & Sons, Inc.
Dynamics of transcriptional and translational processes in hepatocytes cultured in a collagen sandwich
Authors: Dunn James C. Y. , Tompkins Ronald G. , Yarmush Martin L. 
Published: December 2004

AbstractA mathematical model which simulates the dynamic behavior of the hepatocytes cultured in a collagen sandwich is presented. Using several independently determined experimental parameters (e.g., albumin gene nuclear runoff activity, the level of albumin mRNA, and the albumin secretion rate), we have used this model to calculate the in vivo albumin gene transcriptional rate (0.27 molecules per second per hepatocyte), the half‐life of albumin mRNA (3.3 days) in cultured hepatocytes, and the albumin polypeptide elongation rate (10 amino acids per second). In addition, the characteristic time constants for the transient increases in transcription (5 days) and in translation (10 days) were also obtained. These bestfit parameters were used to predict the rate of albumin secretion in rescued hepatocytes. © 1993 John Wiley & Sons, Inc.
Factors affecting the performance of crossflow filtration of yeast cell suspension
Authors: Tanaka Takaaki , Kamimura Ryoji , Itoh Kazutaka , Nakanishi Kazuhiro , Matsuno Ryuichi 
Published: December 2004

AbstractFactors affecting the performance of crossflow filtration were investigated with a thin‐channel module and yeast cells. In crossflow filtration of Saccharomyces cerevisiae cells cultivated with YPD medium (Yeast extract, polypeptone, and dextrose) and suspended in saline, a steady state was attained within several minutes when the cell concentration was low and the circulation flow rate was high. The steady‐state flux and the change in flux during the initial unsteady state were explained well by conventional filtration theory, with the amount of cake deposited and the mean specific resistance to the cake measured in a dead‐end filtration apparatus used in calculation. When the circulation flow rate was lower than a critical value, a part of the channel of the crossflow filtration module was plugged with cell cake, and thus the steady‐state flux was low. In crossflow filtration of suspensions of commercially available baker's yeast, the flux gradually decreased, and the flux after 8 h of filtration was lower than the value calculated by filtration theory. Fine particles contaminating the baker's yeast was responsible for the decrease. A similar phenomenon was responsible for the decrease. A similar phenomenon was observed in crossflow filtration of a broth of S. cerevisiae cells cultivated in molasses medium, which also contains such particles, had no effect of the permeation flux during crossflow filtration. © 1993 John Wiley & Sons, Inc.
Effect of oxygen fluctuations on recombinant Escherichia coli fermentation
Authors: Namdev Pradyumna K. , Irwin Nancy , Thompson B. G. , Gray Murray R. 
Published: December 2004

AbstractEscherichia coli DH5α, carrying the pUC19 plasmid for the lacZ fragment of β‐galactosidase and ampicillin resistance, was grown in a batch fermentor under conditions of fluctuating oxygen supply. A Monte Carlo method was used to control the on/off supply of air to simulate circulation of cells in a large fermentor. Rapid changes in oxygen supply reduced the rates of oxygen uptake the carbon dioxide release and prolonged the active second growth phase in batch culture, compared to growth with continuous aeration. Amplification of the plasmid was observed during the stationary phase when air supplied continuously, but not during the Monte Carlo experiments. © 1993 John Wiley & Sons, Inc.
A Simple genetically structured model of trp repressor–operator interactions
Authors: Koh Boon Tong , Yap Miranda G. S. 
Published: December 2004

AbstractA genetically structured mathematical model of the trp operon based on known molecular interactions of aporepressor, corepressor, and inducer is proposed. The model simulates, both qualitatively and quantitatively, the influence of these regulatory species on the extent of repression and expression of cloned gene products. It shows that at low aporepressor concentration, full repression is not possible even with high tryptophan levels, resulting in leaky expression. Calculations based on the model enabled predictions of optimum levels of aporepressor and tryptophan for effective repression and, concurrently, the β‐indoleacrylic acid concentrations required for induction for both low and high plasmid copy number clones. Using the model we attempted to provide explanations for seemingly anomalous and sometimes contradictory observations by researchers when working with the trp promoter. © 1993 John Wiley & Sons, Inc.
A Simple morphologically structured model describing the growth of filamentous microorganisms
Authors: Nielsen Jens 
Published: December 2004

AbstractBased on the reported mechanisms for filamentous growth, a simple morphologically structured growth model is set up. The model may describe the growth of filamentous microorganisms both on a solid medium and in a submerged culture. For description of a submerged culture the model is combined with a simple population model, which is derived from a balance for the distribution function for the hyphal elements. The model is compared with experimental data for three species of filamentous microorganisms: Geotrichum candidum, Streptomyces hygroscopicus, and Penicillium chrysogenum. © 1993 John Wiley & Sons, Inc.
Diffusivity of Cu2+ in calcium alginate gel beads
Authors: Chen Dong , Lewandowski Zbigniew , Roe Frank , Surapaneni Prasad 
Published: December 2004

AbstractA linear absorption model (LAM) is used to describe the process of metal binding to spherically shaped biopolymers particles. The LAM was solved using a numerical algorithm which calculates diffusivities of metal ion in biopolymer gels. It assumes attainment of rapid metal‐biopolymer binding equilibrium accompanied by rate limiting diffusion of the metal ions through the gel. The model was tested using batch experiments in which copper (Cu2+) binding with calcium alginate beads was investigated. Biopolymer density in the beads was varied between 2% and 5%. The diffusion coefficient of Cu2+ calculated from the LAM ranged from 1.19 × 10−9 to 1.48 × 10−9 m2 s−1 (average 1.31 ± 0.21 × 10−9 m2 s−1), independent of biopolymer density. The LAM has theoretical advantages over the shrinking core model (shell progressive model). The latter calculated an unreasonable exponential increase in the diffusion coefficient as density of alginate polymer in the bead increased. © 1993 John Wiley & Sons, Inc.
Recombinant trypsin production in high cell density fed‐batch cultures in Escherichia coli
Authors: Yee L. , Blanch H. W. 
Published: December 2004

AbstractFed‐batch techniques were employed to obtain high cell density cultures (92–100 g DCW/L) of Escherichia coli strain X90 producing a recombinant serine protease, rat anionic trypsin, secreted to the periplasm. The specific growth rate was controlled to minimize growth‐inhibiting acetate formation by utilizing an exponential feeding profile determined from mass balance equation. The volumetric yield of recombinant rat anionic trypsin was 56 mg/L, and the final cell density was 92 g DCW/L when the culture was induced in the late logarithmic phase. However, when the culture was induced in the early logarithmic phase, the volumetric yield was 13 mg/L and the final cell density was 14 g DCW/L. Thus, the induction timing is shown to have a significant effect on the final cell density as well as the overall volumetric yield of the recombinant protease. © 1993 Wiley & Sons, Inc.
Population and biomass kinetics in fed‐batch cultures of Daucus carota L. somatic embryos
Authors: Huang Li‐Chung , Chi Chung‐Ming , Vits Hugo , Staba E. John , Cooke Todd J. , Hu Wei‐Shou 
Published: December 2004

AbstractThe population dynamics of developing somatic embryos of carrot (Daucur carota L.) was investigated in batch and fed‐batch cultures using modified Murashige and Skoog medium. These substrate limitations coincided not only with stoppage of biomass increase, but also with the increase in total concentration of embryos as well as the advancement of the embryo into a more mature stage. Both glucose and ammonium were depleted from the culture. Restoring either glucose, or ammonium and nitrate, as to approximately initial concentrations in fed‐batch experiments, did not result in a significant increase of the total normal embryo concentration. On the other hand, medium replacement led to increase in biomass concentration, total embryo number, and improved embryo maturity. The addition of a mixture of glucose, ammonium, and nitrate to the spent medium resulted in variable increases in biomass and embryo number, but always less than those resulting from media replacement. Although the total number of embryos was higher after medium replacement, the fraction of embryos reaching torpedo stage was still only 50%. The need for a better means of population characterization for further kinetic studies is discussed. © 1993 Wiley & Sons, Inc.
Stability of bilirubin oxidase in organic solvent media: A comparative study on two low‐water systems
Authors: Skrika‐Alexopoulos Eleftheria , Muir Jacqueline , Freedman Robert B 
Published: December 2004

AbstractThe storage stability of bilirubin oxidase was studied in water‐in‐oil CTAB microemulsions with a chloroformrich continuous organic phase. The kinetics of the inactivation process were best described by a double exponential equation. Approximately half of enzymatic activity was lost during a “fast” phase with a half life of ca. 50 min, whereas the remaining activity was lost much more slowly (half life ca. 1000 min). Rates of inactivation were not affected significantly by variation of either solvent composition or concentration of water droplets, but inactivation was more rapid when droplet size was very small. Steady‐state enzyme kinetics were studied at various stages in the inactivation process, and it was shown that inactivation occurred without change in the Km of the enzyme for bilirubin. Stability was also studied in a liquid/solid two‐phase system; it was found that the inactivation process in this system; it was found that the inactivation process in this system was best described by a single exponential term. The rate was similar to the “fast” phase rate observed in the water‐in‐oil microemulsion system. Inactivation of the enzyme slow. Addition of the surfactant CTAB to the aqueous environment increased the rate of inactivation to levels comparable to those of the “slow” phase observed in water‐in‐oil microemulsions. © 1993 Wiley & Sons, Inc.