bluuebunny/crossref_metadata_2025_split huggingface dataset:
The acetone butanol fermentation on glucose and xylose. II. Regulation and kinetics in fed‐batch cultures
Authors: Fond Olivier , Engasser Jean‐Marc , Matta‐El‐Amouri Ghassam , Petitdemange Henri 
Published: December 2004

AbstractThe kinetics in fed‐batch cultures of acetone butanol fermentation by Clostridium acetobutylicum is compared on glucose, xylose, and mixtures of both sugars. The final conversion yield of sugars into solvents always increases with the sugar feeding rate. At low feeding rates, the sugar concentration in the medium becomes limiting, which results in a slower cellular growth, a slower metabolic transition from an acid to a solvent fermentation and, thus, a higher accumulation of acids. It is only at sufficiently high feeding rates that fed‐batch fermentations yield kinetic results comparable to those of batch fermentations. With mixtures of glucose and xylose, because of a maintained low glucose level, both sugars are taken up at the same rate during a first fermentation period. An earlier accumulation of xylose when the fermentation becomes inhibited suggest that xylose utilization is inhibited when the catabolic flux of glucose alone can satisfy the metabolic activity of the cell. Kinetic results with batch and fed‐batch fermentations indicate several important features of the regulation of C. acetobutylicum metabolism: an early inhibition by the produced acids; an initiation of solvent formation between 4 and 6 g/L acetic and butyric acid depending on the metabolic activity of the cell; a metabolic transition from acids to solvents production at a rate closely related to the rate of sugar uptake; during solvent production, a reassimilation of acids above a minimal rate of sugar consumption of 0.2 h−1; a final inhibition of the fermentation at a total butanol and acids concentration of ca. 20 g/L.
Mathematical model of a batch acetone–butanol fermentation
Authors: Votruba J. , Volesky B. , Yerushalmi L. 
Published: December 2004

AbstractA mathematical model for the batch culture of Clostridium acetobutylicum was formulated using experimental data for anaerobic solvent production. The model summarizes biochemical as well as physiological aspects of growth and metabolite synthesis by the production strain. The key fermentation rates are expressed and evaluated with regard to substrate consumption and butanol end‐product inhibitory effects. Parametric sensitivity analysis of the batch process model was carried out, indicating the importance of the key process parameters.
Rate and yield relationships in the production of xanthan gum by batch fermentations using complex and chemically defined growth media
Authors: Pinches Anthony , Pallent Leslie J. 
Published: December 2004

AbstractRate and yield information relating to biomass and product formation and to nitrogen, glucose and oxygen consumption are described for xanthan gum batch fermentations in which both chemically defined (glutamate nitrogen) and complex (peptone nitrogen) media are employed. Simple growth and product models are used for data interpretation. For nitrogen sources, rate and yield parameter estimates are shown to be independent of initial nitrogen concentrations. For stationary phases, specific rates of gum production are shown to be independent of nitrogen source but dependent on initial nitrogen concentration. The latter is modeled empirically and suggests caution in applying simple product models to xanthan gum fermentations.
Sequential substrate utilization and effectiveness factor in fixed biofilms
Authors: Droste R. L. , Kennedy K. J. 
Published: December 2004

AbstractA mathematical model describing the change in effectiveness factor or effective diffusivity for the intermediate substrate in sequential substrate removal reactions in fixed biofilms is developed. Typical results from the numerical solution of the resulting equation are presented. The production of intermediate substrate in the biofilm increases the conversion of primary substrate to ultimate product in all cases, but the increase is not always significant. Using typical data applying to laboratory anaerobic fermentation studies, it is demonstrated that a small but significant change in reaction kinetics and the effectiveness factor exists.
Effects of Hydroxyurea on immobilized and suspended yeast fermentation rates and cell cycle operation
Authors: Doran Pauline M. , Bailey James E. 
Published: December 2004

AbstractHydroxyurea, an inhibitor of DNA synthesis in Saccharomyces cerevisiae, has been applied in order to restrict growth of immobilized cells. For comparison, the influence of hydroxyurea on suspended S. cerevisiae has also been investigated. Recovery from DNA synthesis inhibition, indicated by measurements of cell growth rate, DNA content, and light scatter properties, occurred faster in immobilized cells than in the suspended yeast. Morphogenesis in both populations was arrested by hydroxyurea, and there was an accumulation of single immobilized and suspended cells with large buds. Synthesis of protein and RNA was not adversely affected in either cell type. The specific rate of ethanol production by immobilized cells increased by an average of 24%, while, for the suspended cells, specific ethanol productivity was up to three times higher. Glucose consumption rates for both cell types also increased under the influence of hydroxyurea. Immobilized cell ethanol yields were reduced by ca. 16% in the presence of hydroxyurea; suspended cell yields were lower by an average of 50%. Total polysaccharide content was reduced by 65% for suspended cells and increased 30% for immobilized cells after hydroxyurea treatment. The data evidence disturbance of the yeast cell cycle due to immobilization.
Dynamics and regulation of sucrose phosphorylase formation in Leuconostoc mesenteroides fermentations
Authors: Vandamme E. J. , Van Loo J. , De Laporte A. 
Published: December 2004

AbstractThe production of Leuconostoc mesenteroides sucrose phosphorylase has been studied in 10‐ and 20‐L batch fermentations. A fermentation medium was devised combining rapid growth, high cell yield, and high enzyme levels. Overall fermentation dynamics and enzyme fermentation patterns are elucidated here in detail. Sucrose is phosphorolyzed into fructose and glucose‐1‐phosphate (G‐1‐P) with G‐1‐P preferentially utilized (thus saving ATP). Subsequently, fructose is gradually metabolized and is also converted to mannitol. Invertase activity is absent. Sucrose phosphorylase is formed transitorily with peak levels toward the end of active growth; a sharp decline in enzyme activity occurs upon further fermentation. The moment of cell (enzyme) harvest is thus critical in view of obtaining active cell or enzyme preparations for sucrose phosphorolysis. Microaerophilic and strictly anaerobic fermentations displayed no appreciable difference in sucrose phosphorylase formation profile. The enzyme is intracellularly located. It is constitutively formed in the absence of sucrose, contrary to that of Pseudomonas species; other disaccharide phosphorylases are not formed.
Factors controlling initial and long‐term ATP regeneration catalyzed by immobilized chromatophores
Authors: Larreta‐Garde Veronique , Thomas Daniel 
Published: December 2004

AbstractPhotosynthetic ATP regeneration was measured in open reactors using immobilized Chromatophores from Rhodopseudomonas capsulata. The influence of several factors on both initial and long‐term ADP photophosphorylation was studied. The effect of phosphate salts and of bovine serum albumin on the organelle activity yield was studied. Photophosphorylation was initiated either with ADP or regenerated ATP and the roles of these nucleotides were compared. Different photoreactor configurations were tested for the production of a phosphorylated compound and a flat reactor selected. The presence of inorganic pyrophosphate in the reaction medium was shown to improve the synthesis of ATP 1.4 times. Using the optimal conditions described here, the total G‐6P production was 50‐fold higher than in batch reactors.
Properties and principles of mycelial flow: A tube rheometer system for fermentation fluids
Authors: Björkman Ulf 
Published: December 2004

AbstractA tube rheometer system has been constructed for aseptic study of the rheology and fundamental flow properties of mycelial fermentation fluids. The rheometer consists of a U‐formed tube circuit starting and ending inside the fermentor. The mash is pumped through the tubes with a lobe rotor pump. The flow is measured by an electromagnetic flow meter. Pressure drops have been measured with a system of differential membrane transducers for different flow rates. The rheometer system was tested with Newtonian and non‐Newtonian fluids.
Scaling oxygen mass transfer in agitated fermentors
Authors: Mooyman Johannes G. 
Published: December 2004

AbstractThere are many scaling formulas that predict the oxygen mass transfer coefficient as kL·a = constant·(Hp/V)αVsβ Exponents α and β frequently are scale dependent themselves. A general formula has been derived from the work of Calderbank,1 Miller,2 and Tilton,3 resulting in kL·a = C1 ϕ + C2 log (Pm/V) ϕ where ϕ equals the gas‐holdup fraction and Pm/V equals the effective mechanical power input per unit of volume. This formula is consistent with the formula of Westerterp4 modified by Miller.2 Gas holdup can be predicted in several ways. Gas‐sparged isothermal expansion power input, used for predicting ϕ, demonstrates that scaling can be done by using either superficial air velocity or volume per volume per minute for aeration.The importance of mixing in replenishing oxygen at the boundary layers of microorganisms will be assessed and compared with the kL·a as the oxygen transfer ratelimiting step.
Vortex chamber for in situ recovery of the antibiotic myxovirescin A in continuous cultivation
Authors: Hecht V. , Vorlop J. , Kalbitz H. , Gerth K. , Lehmann J. 
Published: December 2004

AbstractA vortex chamber for continuous adsorption of the antibiotic Myxovirescin A on XAD resins was developed. In this paper the design and use of the vortex chamber in an external bypass of a continuous process is described. Compared with the normal continuous process, the specific production rate of the antibiotic is four to five times higher when the antibiotic is continuously adsorbed. A semicontinuous process could be performed by using two chambers for adsorption and regeneration alternatively.
Application of extended Kalman filter to identification of enzymatic deactivation
Authors: Caminal G. , Lafuente J. , López‐Santín J. , Poch M. , Solà C. 
Published: December 2004

AbstractA recursive estimation scheme, the Extended Kalman Filter (EKF) technique, was applied to study enzymatic deactivation in the enzymatic hydrolysis of pretreated cellulose using a model previously developed by the authors. When no deactivation model was assumed, the results showed no variation with time for all the model parameters except for the maximum rate of cellobiose‐to‐glucose conversion (r′m).The r′m variation occurred in two zones with a grace period. A new model of enzymatic hydrolysis of pretreated cellulose deactivation was proposed and validated showing better behavior than the old deactivation model. This approach allows one to study enzyme deactivation without additional experiments and within operational conditions.
Acetate addition to an immobilized yeast column of ethanol production
Authors: Vega J. L. , Clausen E. C. , Gaddy J. L. 
Published: December 2004

AbstractAcetate, a by‐product of ethanol fermentation by Saccharomyces cerevisiae, has been shown to inhibit cell growth if present in high concentrations. Consequently, acetate has been considered undesirable in systems where the production rate depends upon steady‐state growth. Acetate, however, may be desirable in some systems since it increases the specific rate of ethanol production by increasing the maintenance requirements of yeast. In immobilized cell reactors using the crosslinking method, steady state is not achieved and cell overgrowth is a problem. This article presents the results of a study aimed at taking advantage of the use of acetate, both to reduce cell overgrowth and to increase productivity. Various concentrations of acetate were added to batch and plug flow systems, while monitoring the effects on cell growth and ethanol production. The productivity was increased by as much as 50% in an immobilized cell reactor (ICR), while cell growth was greatly reduced.
Biological denitrification of drinking water using autotrophic organisms with H2 in a fluidized‐bed biofilm reactor
Authors: Kurt M. , Dunn I. J. , Bourne J. R. 
Published: December 2004

AbstractBiological denitrification of drinking water was studied in a fluidized sand bed reactor using a mixed culture. Hydrogen gas was used as the reaction partner. The reaction kinetics were calculated with a double Monod saturation function. The Ks value for hydrogen was below 0.1% of saturation. No appreciable biofilm diffusion effects were detected. Reactor performance was a function of the culture's past history. Batch experiments always exhibited an accumulation of NO2−, but continuous experiments with a sufficiently long residence time always resulted in complete nitrogen removal. Rates of up to 23 mg N/L h, 25 mg N/g DW h, and 7.9 mg H2/L h were achieved. Residence times of 4.5 h would be required for complete denitrification of water containing 25 mg NO3−–N/L or approximately 1 h for every 5 mg/L.
Transient response of encapsulated enzymes in hollow‐fiber reactor
Authors: Trujillo Edward M. 
Published: December 2004

AbstractA mathematical model for the transient response of encapsulated enzymes is developed showing the effects of the outer boundary layer, the encapsulating membrane, the partition coefficient, and diffusion with reaction within the encapsulating medium. The model incorporates both first‐order kinetics and Michaelis–Menten kinetics for the reaction rate. Using typical hollow‐fiber or microcapsule parameters, the model shows that (a) the partition coefficient affects the overall rate only when the rate‐limiting step is diffusion through the membrane, (b) the transient overall effectiveness factor rises sharply with time and approaches an asymptotic value for most situations, and (c) the first‐order approximation to Michaelis–Menten kinetics is not valid when the initial outside bulk concentration is higher than the Michaelis constant and the overall rate is reaction limited. The model is compared with experimental data using uricase in a hollow‐fiber enzyme reactor configuration. Batch assay and CSTUER (continuous‐stirred ultrafiltration enzyme reactor) studies were conducted on the free enzyme to provide some of the parameters used in the model. The CSTUER data fit the case of substrate inhibition kinetics with the apparent Michaelis constant approaching zero. The hollow‐fiber reactor was conducted with uricase dissolved in both a buffer solution and a concentrated hemoglobin solution. Diffusivities of the solute were measured in both solutions as was the osmotic pressure of the hemoglobin solution. While experimental data for uricase in buffer solution could easily be matched by the model, that in the concentrated hemoglobin solution could not.
Effects of inoculum size on ethanol inhibition modeling and other fermentation parameters
Authors: Vega J. L. , Navarro A. R. , Clausen E. C. , Gaddy J. L. 
Published: December 2004

AbstractThe effects of inoculum size on the kinetics of ethanol fermentation are not well defined in the literature. The purpose of this article is to examine the influence of the initial cell concentration on the modeling of ethanol inhibition. Experimental results show that increasing the inoculum level decreases the severity of ethanol inhibition. The effect of cell concentration can be related to the different inhibitory effects of autogeneously produced versus extracellularly added ethanol. On this basis, it is concluded that the extracellular ethanol concentration in the fermentation media is not the only variable to account for product inhibition modeling. Other fermentation parameters, such as yields and maintenance coefficients, are presented at different levels of initial cell concentration.
Examination of substrate and product inhibition kinetics on the production of ethanol by suspended and immobilized cell reactors
Authors: Daugulis Andrew J. , Swaine Donald E. 
Published: December 2004

AbstractKinetic expressions for the fermentative production of relatively high concentrations [12% (w/v)] of ethanol have been examined. Several expressions which account for both substrate and product inhibition have been formulated, and have been applied to suspended cell and immobilized cell reactors. Experimental data have been used to validate the kinetic expressions used, and the impact of combined inhibition on optimal reactor configuration has been assessed. The process implications of combined substrate and product inhibition for suspended and immobilized cell systems have been discussed.
On the dynamic order of structured Escherichia coli growth models
Authors: Palsson Bernhard O. , Joshi Abhay 
Published: December 2004

AbstractReliable dynamic descriptions of cellular growth are important for many practical applications including bioreactor design and control. A chemically structured growth model of Escherichia coli has been formulated and herein we focus on finding the essential dynamic order of the metabolic part of this model. Standard linear analysis is applied and the main finding is that the model contains three essential modes of motion over the time scale of growth. The doubling time is successfully predicted from an unstable growth motion and the metabolite composition of the three modes of motion suggests that only a three pool metabolic model is necessary. The three pools correspond to important groups of macromolecules; protein, nucleic acids and cell wall constituents.
Production of toluene cis‐glycol by Pseudomonas putida in glucose feb‐batch culture
Authors: Jenkins Richard O. , Stephens Gillian M. , Dalton Howard 
Published: December 2004

AbstractToluene was oxidized by a mutant strain of Pseudomonas putida (strain NG1) to toluene Cis‐Glycol (TCG). Product was accumulated in fed‐batch cultures to concentrations (18–24 g/L) higher than hitherto achieved. In vitro activities of toluene dioxygenase from P. Putida NG1 were fivefold lower than that from the toluene‐grown wild‐type organism, whereas comparable activities of both catechol 2,3‐ and catechol 1,2‐oxygenase were obtained; irreversible inhibition of toluene dioxygenase activity by TCG was shown in vitro. Ammonia deprivation during the production phase limited the growth of revertant organisms but had little effect on either the duration (25h) of the process or the final concentration of TCG achieved. The rate of glucose utilization decreased throughout the biotransformation and cell death accompanied the cessation of TCG accumulation in cultures. These changes were a consequence of TCG formation and a cooperative toxic effect was demonstrated for toluene and TCG. Adenylate energy charge values decreased from ca. 0.8 to 0.2 over the course of the biotransformation but were maintained above 0.5 in the absence of TCG. Similarly, cellular AMP levels increased dramatically during biotransformation, presumably as a consequence of RNA degradation, but were maintained at low levels in the absence of TCG. The results suggest that TCG is the mediate of a gradual deterioration in the state of the culture which leads to a loss of both in vivo and in vitro toluence dioxygenase activity and a marked decrease in culture viability.
Determining pore size distribution in wet cellulose by measuring solute exclusion using a differential refractometer
Authors: Lin J. K. , Ladisch M. R. , Patterson J. A. , Noller C. H. 
Published: December 2004

AbstractSolute exclusion was used to determine the pore volume and micropore size distribution of wet cellulosic materials. Glucose, cellobiose, and polyethylene glycol (PEG) (8 to 130 Å in diameter) were used as molecular probes. Four replicates of cellulosic samples, with each sample being analyzed 4 to 8 times, gave the concentrations of each molecular probe before and after contact with cellulose. Sugar concentrations were determined by the DNS method and PEG concentrations by a differential refractometer. Deviations arising from sample‐to‐sample variability result in variations of solute uptake from which the pore size distribution was determined. The need for replicate samples and a statistical approach to data analysis is indicated. Consequently, the data were fitted to an empirical logistic model function based on the minimum of the residual sum of squares using the finite‐difference, Levenberg‐Marquardt algorithm. A smooth increasing function resulted. We report experimental methodology employing a differential refractometer, common in many laboratories having a liquid chromato‐graph instrument, combined with statistical treatment of the data. This method may also find application in determining pore size distribution in wet, hydrophilic polymers used in some types of membranes, chromatographic supports, and gel‐type resins.
Performance of tapered column packed‐bed bioreactor for ethanol production
Authors: Hamamci Haluk , Ryu Dewey D. Y. 
Published: December 2004

AbstractA tapered column type of bioreactor system packed with immobilized Saccharomyces cerevisiae was used to study the bioreactor performance as a function of design and operating variables. The performance of tapered column bioreactor system was found to be better than that of the conventional cylindrical column reactor system for the ethanol fermentation. The new bioreactor design alleviated problems associated with carbon dioxide evolution and provided a significantly better flow pattern for both liquid and gas phases in the bioreactor without local channelling. A mathematical simulation model, which takes into account of the axial convection and dispersion, interphase mass transfer, and apparent kinetic design parameters, was developed. The effect of radial concentration gradients on the bioreactor performance was found to be insignificant. For the reactor system studied, the maximum ethanol productivity obtained was 60 g ethanol/L gel/h, and the maximum glucose assimilation rate was 140 g glucose/L gel/h. One of the most important findings from this study was that the apparent kinetic parameters change at the glucose concentration of 2 g/L This change was found to be due to the changes in yeast physiology and metabolism. The values of V and V decreased from 0.8 to 0.39 g ethanol/g cell/h and from 97mM to 11mM, respectively. The substrate inhibition constant was estimated as 0.76M and the product inhibition constant was determined as 113 g ethanol/L The degree of product inhibition showed practically a linear relationship with an increasing ethanol concentration. Based on the hydro‐dynamic analysis of the bioreactor system, it was found that the Peclet number, NPe was not a strong function of the flow velocity at low flow rates through the bioreactor system, but its value decreased somewhat at an interstitial velocity greater than 0.03 cm/s. The tapered column bioreactor system showed a much better flow pattern of gas and liquid phases within the reactor, thereby providing a more homogeneous distribution of gas–liquid–solid phases in the reactor without any phase separation.