bluuebunny/crossref_metadata_2025_split huggingface dataset:
Production of ethanol by Clostridium thermosaccharolyticum: II. A quantitative model describing product distributions
Authors: Mistry Firoz R. , Cooney Charles L. 
Published: December 2004

AbstractThe study of the continuous culture of Clostridium thermosaccharolyticum on xylose showed multiple steady states and hysteresis. A quantitative model based on the biochemistry and physiology of xylose fermentation by C. thermosaccharolyticum was developed. The objective in developing this model was to bring together the observations both of this study and of other researchers on the fermentation of xylose. The model equations were written based on the metabolic pathway for xylose utilization by C. thermosaccharolyticum and the requirement that the carbon, ATP, and NADH within the cell be balanced. Given the specific growth rate μ and the specific xylose utilization rate qs, a set of product distributions (ethanol, acetate, and lactate) satisfying these balances was obtained. This set was plotted on a triangular plot and named the permitted region. The product distributions within this permitted region were shown to be affected by the environmental parameters such as iron concentration and hydrogen partial pressure. The model predicted trends in product distribution which correlate with experimentally observed phenomena. The model was also used to analyze the continuous‐culture data from our experimental work.
Membrane filtration affinity purification (MFAP) of dehydrogenases using cibacron blue
Authors: Ling T. G. I. , Mattiasson B. 
Published: December 2004

AbstractThe method for purification of biomolecules by a combination of affinity interactions and membrane filtration for separation of unwanted material has been found to be of interest for large‐scale work. This study examines the suitability of silica nanoparticles as carriers in the process. Alcohol dehydrogenase and lactate dehydrogenases were chosen as target molecules to be purified. The binding capacity was found to be comparative to what is obtained for high‐performance liquid chromatography (HPLC) packing material. Both binding and desorption of the enzymes were found to be effective. The limiting factor of the process was the filtration flow rate.
Cell counting and carbon utilization velocities via microbial calorimetry
Authors: Boe Irwin , Lovrien Rex 
Published: December 2004

AbstractBacteria rapidly metabolize sugars and produce heat accordingly (Escherichia coli, aerobic conditions, 25°C). Two kinds of heat output are gotten: (1) from excess cells and limiting carbon, 2 × 109 to 5 × 109 cells, 5‐50 nanomole glucose; (2) from limited cells and excess carbon, 0. 1 × 109‐1 × 109 bacteria and 200‐600 nmol glucose. The thermograms from heat conduction calorimetry under the first conditions measure velocities of sugar uptake and initial metabolic throughput in 1‐6‐min time spans before a growth cycle possibly can occur. Under the second conditions with limited cells, power output plateaus to a steady state proportional to cell biomass and number of cells. In order to evaluate the calorimetric means for measuring number of cells, six independent means including spectrophotometry (turbidity) were compared: microkjeldahl nitrogen, biuret protein, dry weight, microscopy direct counting in Petroff‐Hausser chambers, and viable colony counting. Using turbidity as a central standard, all methods including calorimetry under the second set of conditions agree within ±18% of one another. Spectrophotometry is the most rapid method but is seriously interfered with by pigments that absorb and foreign particles that also scatter. Calorimetry requires 10‐30 min but measures cell numbers in opaque samples impossible for optical means.
Oxygen transfer rates in a mammalian cell culture bioreactor equipped with a cell‐lift impeller
Authors: Johnson M. , André G. , Chavarie C. , Archambault J. 
Published: December 2004

AbstractMeasurements of kLa were carried out in 1. 5‐ and 5‐L New Brunswick Scientific CelliGen® bioreactors. The measured kLa in water were identical for both vessel sizes operated in similar condition. The mass transfer rate increased with temperature, mixing speed, and aeration rate, with this last parameter being the most significant. Surface aeration alone gave kLa values of 0. 4 to 1. 6 h−1. A 25% decrease in kLa was observed above an aeration rate of 1. 6 vvm. This was caused by the particular foam breaker of the CelliGen bioreactor. Measurements of kLa using a mammalian cell culture medium supplemented with 5% fetal calf serum (FCS) have confirmed the negative effect of the foam breaker on kLa The measured value in this medium was 1. 2 h−1 for all aeration rates, more than 60% of which was attributed to surface aeration.
Reasons for the apparent difference in the effects of produced and added ethanol on culture viability during rapid fermentation by Saccharomyces cerevisiae
Authors: Dasari G. , Worth M. A. , Connor M. A. , Pamment N. B. 
Published: December 2004

AbstractBy feeding ethanol at various high rates to low cell density cultures of Saccharomyces cerevisiae it was shown that the sharp fall in viability when ethanol is produced during rapid fermentations is in part a direct consequence of the high rate of change of extracellular ethanol concentration. Nevertheless, the fall in viability in high cell density rapid fermentations which produced 98 g L−1 ethanol in 3 h considerably exceeded that of control low cell density cultures to which ethanol was added at the same rate. This difference was shown to be not due to intracellular ethanol accumulation or to differences in glucose concentration between the cultures. The concentrations of a range of potentially toxic fatty acids, higher alcohols, and esters were measured during rapid fermentations, but when added at these concentrations to control cultures in the presence of ethanol they had no significant toxic effect. However, when rapid fermentations were conducted in rich medium containing 80 g L−1 yeast extract, the apparent difference in toxicity of produced and added ethanol virtually disappeared. Magnesium was shown to be the component of yeast extract primarily responsible for this effect. The high rate of fall of viability when ethanol is rapidly produced is suggested to be partly due to the inability of the cells to adapt quickly enough to the rising ethanol concentration and partly to an increased demand for magnesium at higher ethanol concentrations which cannot be met in Mg‐unsupplemented high cell density fermentations.
Enzyme loading in a solid support with nonuniform pore size distribution
Authors: Chiang C. L. , Wu T. C. , Wang Y. J. 
Published: December 2004

AbstractThe concept of pore size distribution is incorporated into the Clark model of enzyme immobilization in the present study. This refined model predicted that in the case of small harmonic pore radius with the same surface area and porosity of the support, more enzyme could be loaded in a support with nonuniform pores than that with uniform pores. In comparing the enzyme loading efficiency of the support with two different pore size distributions, the one with Gaussian distribution had the greater amount of enzyme immobilized than the other one with Rajagopalan's distribution. Furthermore, more enzyme could be loaded in a support with wider Gaussian pore size distribution than that with narrower distribution. The immobilized enzyme profile in the solid support with pore size distribution displayed a stepwise pattern which differed appreciably from the sigmoidal profile predicted for the support with uniform pore size. This stepwise enzyme distribution profile became sigmoidal with decreasing hT or increasing k. The new model could be used for designing protocols for an enzyme immobilization process.
New method of immobilization of microbial cells by capture on the surface of insoluble pyridinium‐type resin
Authors: Kawabata Nariyoshi , Nishimura Sadaki , Yoshimura Tohru 
Published: December 2004

AbstractA new method for the immobilization of microbial cells has been developed. Whole cells of Escherichia coli with aspartase activity were immobilized by capture on the surface of cross‐linked poly(N‐benzyl‐4‐vinylpyridinium bromide) containing styrene (BVPS resin), an insoluble pyridinium‐type resin. When a suspension of the bacterial cells in buffer solution was passed through a glass column containing beads of BVPS resin, the cells were captured on the resin surface and formed an immobilized cell system. A fixed‐bed column reactor containing 300 mg of the bacterial cells immobilized by capture on 10 g of BVPS resin beads was used for the preparation of L‐aspartic acid from ammonium fumarate. Continuous operation of tne bioreactor produced L‐aspartic acid in a quantitative yield when the influent substrate concentration was 0.1M and the flow rate was 0.41–0.83 bed volumes per hour at pH 7.4–7.7 at 30°C.
Elucidation of the cytoplasmic and vacuolar components in the inorganic phosphate region in the 31P NMR spectrum of yeast
Authors: Shanks Jacqueline Vanni , Bailey James E. 
Published: December 2004

AbstractSubcellular compartments, such as the vacuole in yeast, play important roles in cell metabolism and in cell response to external conditions. Concentrations of inorganic phosphate and pH values of the vacuole and cytoplasm were determined for anaerobic Saccharomyces cerevisiae cells based upon 31P NMR spectroscopy. A new approach allows the determination of these values for the vacuole in cases when the resonance for inorganic phosphate in the cytoplasm overlaps with the resonance for inorganic phosphate in the vacuole. The intracellular inorganic phosphate resonance was first decomposed into two components by computer analysis. The assignments of the components were determined from in vivo correlations of Pi chemical shift and the chemical shifts of the cytoplasmic sugar phosphates, and the pH dependency of the resonance of pyrophosphate and the terminal phosphate of poly‐phosphate (PP1) which reside in the vacuole. An in vivo correlation relating PP1 and P chemical shifts was established from numerous evaluations of intracellular compositions for several strains of S. cerevisiae. This correlation will aid future analysis of 31P NMR spectra of yeast and will extend NMR studies of compartmentation to cellular suspensions in phosphate‐containing medium. Application of this method shows that both vacuolar and extracellular Pi were phosphate reserves during glycolysis in anaerobic S. cerevisiae. Net transport of inorganic phosphate across the vacuolar membrane was not correlated with the pH gradient across the membrane.
Production of L‐phenylacetyl carbinol by immobilized yeast cells: II. Semicontinuous fermentation
Authors: Mahmoud Wafaa M. , El‐Sayed Abdel‐Halim M. M. , Coughlin Robert W. 
Published: December 2004

AbstractThe cyclic, semicontinuous production of L‐phenylacetyl carbinol (L‐PAC) from a benzaldehyde substrate by Saccharomyces cerevisiae ATCC 834 immobilized in calcium alginate beads was substantially enhanced to about 4.5 g/L in a second cycle by reactivation in fresh medium for 24 h, following an earlier 24‐h period of production from substrate. Intermittent feeding of benzaldehyde was employed (four doses in 3 h). In subsequent similar cycles, however, the production returned to that produced in the first cycle, viz. L‐PAC concentration of 2–3 g/L in the medium. Production of L‐PAC was also increased by adaptation of the cells over 200 h of exposure to the benzaldehyde substrate (compared to wild‐type cells) and by continuous (as compared to intermittent) feeding of the substrate. A liter as great as 10 g/L was obtained with wild‐type cells by continuous feeding of benzaldehyde over 6 h. Immobilization not only protected the cells from toxic effects of substrate but also permitted them to be used during 7 cycles of semicontinuous operation over more than 200 h.
Calorimetric control of fed‐batch fermentations
Authors: Randolph T. W. , Marison I. W. , Martens D. E. , von Stockar U. 
Published: December 2004

AbstractMeasurements of the heat produced by Saccharomyces cerevisiae CBS 426 were used in conjunction with elemental and enthalpic balances to control fed‐batch fermentations. A proportional control using the ratio of carbon dioxide evolution rate to heat production resulted in high biomass yields and minimal ethanol production. For the special case where the carbon source contains no nitrogen, biomass production estimated from heat measurements agreed well with measured values. When the controller gain was set below the maximum specific cellular growth rate, stable control was achieved, even in response to large upsets in feed concentrations.
Population dynamics of a recombinant culture in a chemostat under prolonged cultivation
Authors: Weber Allison E. , San Ka‐Yiu 
Published: December 2004

AbstractThe dynamics of a chemostat culture of Escherichia coli K12 harboring plasmid pBR322 under prolonged cultivation with a nonselective complex medium were studied. The ability of the culture to form colonies on plates supplemented with different ampicillin concentrations was monitored. It was observed that almost all cells sampled were able to grow on a high concentration of ampicillin at the beginning of the experiment. However, a subpopulation which formed colonies on intermediate‐concentration (500–1000 mg/L) plates, but not on a high‐concentration (2000 mg/L) plate, was detected just before the appearance of the plasmid‐free cells. As time progressed, the percentage of this subpopulation increased, reached a maximum, then decreased toward the end of experiment. At this time the culture was dominated by a subpopulation which could not form colonies on the 100 mg/L ampicillin plates. These results indicate that three major processes may occur in the chemostat: a gradual shift of the higher plasmid copy number population toward a relatively lower copy number population; the complete shedding of the plasmid due to faulty segregation of plasmids during cell division; and growth competition among the subpopulations. A previously derived model is extended to account for all subpopulations. The model agrees qualitatively with the experimental results.
Cell growth and death rates as factors in the long‐term performance, modeling, and design of immobilized cell reactors
Authors: Dale M. C. , Chen C. , Okos M. R. 
Published: December 2004

AbstractThe viable fraction of immobilized cells in a bioreactor may be critical in predicting long‐term or steady‐state reactor performance. The assumption of near 100% viable cells in a bioreactor may not be valid for portions of immobilized cell reactors (ICRs) characterized by conditions resulting in appreciable death rates. A mathematical model of an adsorbed cell type ICR is presented in which a steady‐state viable cell fraction is predicted, based on the assumptions of no cell accumulation in the reactor and a random loss of cells from the reactor. Data on cell death rates, cell growth rates, and productivity rates as functions of temperature, substrate, and ethanol concentration for the lactose utilizing yeast K. fragillis were incorporated into this model. The steady‐state reactor viable cell fraction as predicted by this model is a strong function of both temperature and ethanol concentration. For example, a stable 20% viable fraction of the immobilized cells is predicted in ICR locations experiencing continuous conditions of either 30 g/L ethanol at 40°C, or 95 g/L ethanol at 25°C. Steady‐state ICR “plug flow” concentration profiles and column productivities are predicted at three operating temperatures, 20, 30, and 40°C using two different models for ethanol inhibition of productivity. These profiles suggest that the reactor operating temperature should be low if higher outlet ethanol concentrations are desired. Three reactor design strategies are presented to maximize the viable cell fraction and improve long‐term ethanol productivity in ICR's: (1) reducing outlet ethanol concentrations, (2) rotating segments of an ICR between high and low ethanol environments, and (3) simultaneous removal of the ethanol produced from the reactor as it is formed.
Modeling of enzyme‐potentiometric sensors involving acid‐ or base‐forming reactions
Authors: Ogundiran Sunday O. , Varanasi Sasidhar , Ruckenstein Eli 
Published: December 2004

AbstractEnzyme‐potentiometric sensors in which the chemical conversion of the analyte leads to the formation of an acid and/or a base can often display complex response characteristics. In these sensors, the, electrochemically monitored species is usually the H+ ion (pH‐based sensors). However, in some cases the conjugate‐ion of the H+ (or OH−) ion of the acid (or base) produced‐can also be monitored—a specific example being the urease–NH4+ sensor. The response of both types of sensors is strongly affected by: (1) the degree of dissociation of the products and their transport properties in the enzymic film, (2) the amounts of pH‐buffers present in the test solution, (3) the test solution's pH, and (4) the diffusion coefficients of the various species. In this article, a previously developed theoretical model for pH‐based sensors—in which the differences in diffusivities of the various species were ignored—is generalized to accommodate for such differences, and extended to the latter of the above two types of sensors. It is shown that when the sensor operates under analyte diffusion‐controlled conditions, the response of either type of sensor can be predicted by a simple algebraic equation which is independent of the actual kinetics of the enzymic reaction.
Influence of dilution rate and induction of cloned gene expression in continuous fermentations of recombinant yeast
Authors: Da Silva Nancy Anderson , Bailey James E. 
Published: December 2004

AbstractThe effects of growth rate on cloned gene product synthesis in recombinant Saccharomyces cerevisiae have been studied in continuous culture. The plasmid employed contains a yeast GAL10‐CYC1 hybrid promoter directing expression of the E. coli lacZ gene. β‐Galactosidase production was therefore controlled by the yeast galactose regulatory circuit, and the induction process and its effects were studied at the various dilution rates. At all dilution rates plasmid stability decreased with induction of lacZ gene expression. In some instances, two induced “steady states” were observed, the first 10–15 residence times after induction and the second after 40–50 residence times. The second induced steady state was characterized by greater biomass concentration and lower β‐galactosidase specific activity relative to the first induced “steady‐state.” β‐Galactosidase specific activity and biomass concentration increased as dilution rate was reduced, and despite lower flow rate and plasmid stability, overall productivity (activity/L/hr) was substantially higher at low dilution rate. Important factors influencing all of the trends were the glucose and galactose (inducer) concentrations in the vessel and inducer metabolism.
A novel magnetic silica support for use in chromatographic and enzymatic bioprocessing
Authors: Goetz Victor , Remaud Magali , Graves David J. 
Published: December 2004

AbstractA limited number of support matrices have so far been developed for use in magnetically stabilized fluidized bed (MSFB) applications. We have developed a versatile magnetic silica support which can be derivatized readily for both adsorption chromatography and enzyme immobilization by well‐known techniques. A magnetic pellicular bead is prepared by electrostatically depositing alternating layers of colloidal silica and cationic polymer onto macroscopic nickel core particles. The polymer is then burned out and the silica partially sintered to yield a porous shell with 5–80 m2/g of surface area. This magnetic composite was tested as a support for immobilizing invertase. Sucrose was continuously converted to its component monosaccharides with nearly constant activity over the first 8 days and retention of 50% of initial activity after 25 days.
Strategies for reducing solvent toxicity in extractive fermentations
Authors: Yabannavar V. M. , Wang D. I. C. 
Published: December 2004

AbstractThe toxicity of an Alamine 336/oleyl‐alcohol extraction system on Lactobacillus delbrueckii was investigated. It was shown that the solvent affected the cells through the water‐soluble portion and the immiscible portion of the solvent. While immobilization significantly protected the cells from the immiscible solvent phase, the water‐soluble part of the solvent still caused toxicity to the microorganisms due to diffusion of the solvent into the matrix. Adding soybean oil to the κ‐carrageenan matrix could trap the diffusing solvent molecules, and therefore reduce the toxic effect from the water soluble portion of the solvent. The protective ability of soybean oil was quantified through mathematical modeling and experimentation.
High‐concentration cultivation of Lactococcus cremoris in a cell‐recycle reactor
Authors: Bibal Bernard , Vayssier Yves , Goma Gérard , Pareilleux Alain 
Published: December 2004

AbstractHigh‐cell concentration cultivation of Lactococcus cremoris, a homofermentative lactic acid producer, in a cell‐recycle fermentor is described. Cross‐flow filtration allowing continuous removal of the inhibitory metabollte, the influence of dilution rate on growth was investigated in total or partial cell‐recycle cultures. The dependence of growth characteristics on operating conditions was identified and quantified using lactose as the carbon source. Growth kinetics could be described by both lactate removal efficiency and nutrient availability. Based on physiological observations, biomass and lactic acid productivities were predicted in partial cell‐recycle cultures.
Characterization of immobilized cell growth rates using autoradiography
Authors: Stewart Philip S. , Karel Steven F. , Robertson Channing R. 
Published: December 2004

AbstractThe growth of immobilized Escherichia coli was analyzed by pulse‐chase radioisotope labeling of the cell mass with 35SO42− and subsequent liquid emulsion autoradiography of thin cross sections of the cell aggregate. Bacteria were retained in a planar aggregate on a microporous membrane and grown anaerobically on a phosphate‐buffered medium with glucose as the sole carbon and energy source. A mathematical model of immobilized cell growth and convection was used to predict the distribution of label in the cell mass and permit information about both the magnitude and variation in the intrinsic growth rate to be extracted. Growing zone dimensions ranging from 4 to 48 μm and growth rates from 0.28 to 0.5 h−1 were found. Data collected at low glucose concentrations were consistent with a zero‐order description of intrinsic growth kinetics. At high glucose concentrations, conditions under which the system was subject to significant pH inhibition, the data were best described by the prediction of a first‐order kinetic model. When coupled with a suitable analytical framework, the combination of radioisotope labeling and autoradiography provides a general method for characterizing immobilized cell growth rates.