bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Hydroxyurea on immobilized and suspended yeast fermentation rates and cell cycle operation
Authors: Doran Pauline M. , Bailey James E.
Published: December 2004

Hydroxyurea, 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

The 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

Photosynthetic 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

A 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

There 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

A 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

A 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

Acetate, 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

Biological 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

A 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

The 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

Kinetic 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

Reliable 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

Toluene 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

Solute 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

A 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.
A new immobilized cell system with protection against toxic solvents
Authors: Tanaka Hideo , Harada Satoru , Kurosawa Hiroshi , Yajima Mizuo
Published: December 2004

A new immobilized cell system providing protection against toxic solvents was investigated so that normal fermentations could be carried out in a medium containing toxic solvents. The system consists of immobilized growing cells in Ca‐alginate gel beads to which vegetable oils, which are inexpensive absorbents of solvents, had been added. The ethanol fermentation of Saccharomyces cerevisiae ATCC 26603 was used as a model fermentation to study the protection afforded by the system against solvent toxicities. The fermentation was inhibited by solvents such as 2‐octanol, benzene, toluene, and phenol. Ethanol production of one batch was not finished even after 35 h using immobilized growing yeast cells in conventional Ca‐alginate gel beads in an ethanol production medium (5% glucose) containing 0.1% 2‐octanol, which is used as a solvent for liquid‐liquid extraction and is one of the most toxic solvents in our experiments. With the new immobilized growing cell system using vegetable oils, however, four repeated batch fermentations were completed in 35 h. Castor oil provided even more protection than soy bean, olive, and tung oils, and it was possible to complete six repeated batches in 35 h. The immobilized cell system with vegetable oils also provided protection against other toxic solvents such as benzene and toluene. A possible mechanism for the protective function of the new immobilized cell system is discussed.
Immobilization of activated sludge by PVA–boric acid method
Authors: Hashimoto Susumu , Furukawa Kenji
Published: December 2004

A new method (polyvinyl alcohol–boric acid method) for an inexpensive and effective immobilization of activated sludge was developed. Using activated sludge immobilized by this PVA–boric acid method, synthetic waste‐water was treated at a high loading rate of 0.5–2.35 kg TOC/m3 day. Total organic carbon and total nitrogen were removed at efficiencies of 93 and 30–40%, respectively. The kinetic constants Y and b for this immobilized activated‐sludge process were determined to be 0.594g mixed liquor suspended solids (MLSS)/g TOC and 0.0219 day−1, respectively. The cost calculation of chemicals required for the immobilization of activated sludge by this PVA–boric acid method was proved to be extremely inexpensive for the immobilization of activated sludge.
Inexpensive, rapid procedure for bulk purification of cellulase‐free β‐1,4‐D‐xylanase of high specific activity
Authors: Tan Larry U. L. , Yu Ernest K. C. , Louis‐Seize Gerald W. , Saddler John N.
Published: December 2004

A process has been developed for the bulk purification of cellulase‐free β‐1,4‐D‐xylanase from the fungus Trichoderma harzianum E58. The process involved the primary step of ultrafiltering the culture filtrate via a 10,000‐molecular‐weight cut‐off membrane to separate the cellulase (retentate) and xylanase (permeate) fractions. The cellulase component was concentrated by 40‐ to 60‐fold, resulting in an enzyme complex that could effectively hydrolyze high concentrations of cellulose and xylan to glucose and xylose. The xylanase was concentrated and solvent exchanged by adsorption to a cationic exchanger, SP‐ZetaPrep 250, followed by elution with a pH change in the buffer to give a purified and concentrated xylanase complex dissolved in a low‐salt buffer. The resultant xylanase system was pure by the criteria of sodium dodecyl sulfate polyacrylamide electrophoresis, had a very high specific activity of 2400 IU/mg protein, was virtually free of filter paper activity, and had a ratio of contaminating filter paper activity of 2 × 10−6 (0.009% endoglucanase activity). Approximately 3.3 g protein, which contained in excess of 7 × 106 IU xylanase activity, was obtained from 17 L original culture filtrate. The process scheme was designed to facilitate scale‐up to an industrial level of production.
Dynamic analysis of irreversible adsorption of protein on porous polymer resins as studied by pulse injection method
Authors: Nakamura Katsunori , Hirai Youhei , Kitano Hiromi , Ise Norio
Published: December 2004

Irreversible adsorption of bovine serum albumin onto porous polymer resins is examined by a pulse injection method. The experimental results are theoretically analyzed by a model based on the assumption that there exist three kinds of binding sites with different binding rates, which are considered to exist in the vicinity of the outer periphery surface, the inner surface of macropore, and the micropore, or center part, of particles. The three kinds of adsorption rates are also evaluated by a batch method and are nearly equal to the corresponding kinetic parameters by this method. The amount of BSA bound irreversibly to the resins is independent of the protein concentration and the flow rate examined, which suggests that protein molecules penetrate into pores of resins and occupy almost all the effective binding sites in the resins. The total amount of bound BSA shows a pH dependence with a maximum near the isoelectric point of BSA, and the amount of BSA bound at the slowest rate is most largely influenced by pH.
Lipase‐catalyzed ester exchange reactions in organic media with controlled humidity
Authors: Goderis H. L. , Ampe G. , Feyten M. P. , Fouwé B. L. , Guffens W. M. , Van Cauwenbergh S. M. , Tobback P. P.
Published: December 2004

Immobilized lipase activity is studied in organic solvent systems of controlled water content under the influence of a variety of reaction parameters, such as temperature, relative humidity, substrate concentrations, and type of fatty acid used. Control of the amount of water in the reaction system was found to be a valuable tool for the orientation of the reaction process and for the determination of the final reaction products. The properties of the immobilized lipase were studied using the interesterification of triolein and palmitic acid as the model system.
Gibberellic acid by solid state fermentation: Consistent and improved yields
Authors: Kumar P. K. R. , Lonsane B. K.
Published: December 2004

Five strains each of Gibberella fujikuroi and Fusarium monoliforme were screened to select G. fujikuroi P‐3, a strain capable of giving consistent production of gibberellic acid (GA3) by solid state fermentation (SSF). The comparative production of GA3 by SSF and submerged fermentation (SmF) indicated better productivity with the former technique. The accumulation of GA3 was 1.626 times higher in the case of SSF. On the basis of available carbohydrates in the media, the percent conversions were 0.096 and 0.156 in SmF and SSF, respectively. The use of coarse wheat bran of the particle size of 0.3–0.4 cm resulted in an increase of 2.5 times in the yield of GA3. The enrichment of commercial wheat bran with soluble starch gave enhanced accumulation to an extent of 3.5 times. The relation between GA3 production and cell growth in SSF was similar to that encountered in SmF. The consistent and improved yields to a tune of 1.22 g GA3 per kilogram dry moldy bran (DMB) establish the potential and feasibility of SSF for the production of GA3 by G. fujikuroi P‐3. On preliminary cost analysis, a net savings of about 60% and 50% on fermentation medium cost and the expenditure on down‐stream processing, respectively, as compared to the presently employed SmF technique was evident.
Cell cycle analysis of plasmid‐containing Escherichia coli HB101 populations with flow cytometry
Authors: Seo Jin‐Ho , Bailey James E.
Published: December 2004

The relationship between cell mass and cell number dynamics for bacteria such as Escherichia coli depends on the cell cycle parameters C and D. Effects of plasmid copy number on these cell cycle parameters have been studied for Escherichia coli HB101 containing pMB1 plasmids propagated at different copy numbers ranging from 12 to 122. Determination of cell cycle and cell size parameters was accomplished using flow cytometry data on single‐cell light scattering and DNA content frequency functions in conjunction with a mathematical model of cell population statistics. Two independent methods for estimating C and D intervals based on flow cytometry were developed and applied with essentially identical results. The presence of plasmids decreases the C and D periods, mean cell sizes, and initiation masses for chromosome replication by 14, 24, 38, and 18%, respectively, relative to corresponding values for plasmid‐free host cells. Plasmid copy number has a negligible influence on these parameters, suggesting that host‐plasmid inter actions which determine these properties are centered on the single plasmid selected for replication according to the random selection model established for ColE1‐type plasmids.
Reaction rate calculations for cosubstrates diffusing into catalyst layer from opposite sides
Authors: Karel Steven F. , Robertson Charming R.
Published: December 2004

The effects of diffusion on a reaction taking place in a permeable catalyst are examined theoretically for the case where the reaction has two substrates supplied from opposite sides of a catalytic slab. The solutions of the reaction–diffusion equation for combinations of zeroth‐and first‐order kinetics are given in terms of an effectiveness factor and a parameter describing the position in the layer where the reaction occurs. In these terms, the results vary only weakly with reaction order. The use of the exact solutions for a reaction that is zeroth order in both sub strates is proposed as a general rule for estimating the reaction rate and the reaction position.
Ionic binding of biologically active proteins on cross‐linked acrylic macromolecular supports
Authors: Maxim Steliana , Flondor Aurelia , Carpov Adrian
Published: December 2004

The immobilization process of some biologically active proteins on acrylic ion exchange supports was studied. The cross‐linking and swelling coefficient, as well as the molecular weight of the enzyme, were proved to influence the immobilization process. The kinetic data indicate mainly a binding process controlled by diffusion. The uptake coefficient values of different proteins ranged between 35.0 and 98.0%. The laboratory experiments per formed with some of the obtained enzymic preparation certify the preservation of the catalytic activity following the immobilization process.
The modeling and analysis of the elution stage of biospecific adsorption in fixed beds
Authors: Arve B. H. , Liapis A. I.
Published: December 2004

A mathematical model that describes the dynamic behavior of the elution stage of biospecific adsorption (affinity chromatography) in a fixed bed is developed and solved. Both non‐selective and selective elution methods are considered. The results show that the duration of the elution stage for a given bed length decreases as the value of the Porath parameter for elution increases. The concentrating effect of the elution stage on the adsorbate of interest increases as the bed length and the value of the Porath parameter for elution increase. It is shown that it is inappropriate to assume that the eluent is infinitely fast distributed within the pores of the particles, and an interesting result involving a local maximum in the effluent concentration of the selective eluent is obtained when the direction of flow in the elution stage is the same as in the adsorption and wash stages and the bed length is large. When the direction of flow during elution is opposite (as compared to being the same) to that employed in the adsorption and wash stages, a shorter total elution time is obtained. The advantage gained with a reversed flow increases as the bed length decreases.
Calorimetric investigation of aerobic fermentations
Authors: Birou Bernard , Marison Ian W. , Stockar Urs Von
Published: December 2004

A modified bench scale calorimeter has been employed to determine the heat generated by various microbial strains growing on a range of different substrates, covering degrees of reduction from 3 to 6.13. The results are analyzed, and interpreted in the light of coupled enthalpy and elemental balances. The heat released by the microbial cultures has been found to correlate linearly with other process variables, such as biomass generation and oxygen uptake. The ratio between the heat generated and the biomass formed, the so‐called “heat yield” (YQ/x), has been shown both on theoretical and experimental grounds to increase with increasing degree of reduction of the substrate and to decrease with increasing biomass yield. The two effects could be combined into a simple model which permits the amount of heat released per unit of biomass formed to be predicted from the degree of reduction of the substrate as the only independent variable. The ratio between the heat generated and the oxygen taken up was constant at 440 kJ (mol O2)−1 throughout all experiments as expected from theoretical considerations for strongly aerobic processes.
Noninferior periodic operation of the metabolite producing biological reactor
Authors: Hasegawa Sachiyuki , Matsubara Masakazu , Shimizu Kazuyuki
Published: December 2004

The optimal periodic operation of the biological reactor in which the metabolites belonging to Type I or II in Gaden's classification are produced was investigated from the viewpoint of the multiobjective programming problem. In addition to the productivity of the desired product, its concentration and the conversion of the substrate which have a large influence on the performance of the separation process following the fermentation process were adopted as the objective functions. The growth of cells was assumed to be inhibited both by the substrate and the product, and the Luedeking‐Piret model was employed for the specific production rate. The optimal periodic operation was determined by use of the optimization method due to Miele. It was clarified that the noninferior set for the periodic operation was generally composed of the repeated batch portion and the repeated fed‐batch one.
Single‐step unimolecular non‐first‐order enzyme deactivation kinetics
Authors: Sadana Ajit , Henley James P.
Published: December 2004

A two‐parameter deactivation model is proposed to describe the kinetics of activity stabilization for some enzymes. The single‐step unimolecular mechanism exhibits non‐first‐order deactivation kinetics since the final enzyme state, E1 is not completely inactivated. The usefulness of the model is demonstrated by applying it to the inactivation of different enzymes. The influence of the concentration of active ester, ionic strength, and pH on the model parameters is examined during the inactivation of electric eel acetylcholinesterase.25 In general, inactivators would decrease the level of activity stabilization, α1, and increase the first‐order inactivation rate constant, k1. The effect of protecting agents would be to increase α1 and to decrease k1.
Quantification of the degree of acclimation of a mixed culture to an industrial landfill leachate
Authors: Evans Patrick J. , Ahlert Robert C.
Published: December 2004

Quantification of the degree of acclimation of a mixed culture is demonstrated. An industrial landfill leachate was used as a model mixed substrate. The biodegradable fraction, the specific rate of substrate uptake, and the apparent reaction order were measured. The method of acclimation did not appear to affect the biodegradable fraction. The apparent reaction order is shown to be related to the difference between the rates of uptake of the various leachate components. This difference is defined as the differential in the rate. The effects of a supple mental carbon source and different inocula were investigated. Addition of glucose tends to diminish the differential but also decreases the specific rate of substrate uptake. The outcome of an acclimation procedure is dependent on the quality of the inoculum; however, a poor inoculum does not preclude an acclimation that yields a superior culture. A normalized rate coefficient is shown to have merit as an indicator of the degree of acclimation. Two microorganisms were isolated, Acinetobacter calcoaceticus var. Iwoffi and Moraxella sp., that could grow axenically with the leachate as their sole source of carbon. Comparisons are made between pure and mixed cultures with regard to biodegradable fraction, specific rate of substrate uptake, and apparent reaction order.
Enzymatic synthesis of L‐cysteine
Authors: Hsiao Humg‐Yu , Wei Tena
Published: December 2004

O‐Acetylserine sulfhydrase in the form of a crude extract from Salmonella typhimurium LT2 was used for the production of L‐cysteine from L‐O‐acetylserine and sodium hydrosulfide at pH 7.0 and 25°C. The two substrates have quite different pH stability relationships. O‐Acetylserine readily rearranges to N‐acetylserine and the rate of this O → N acyl transfer reaction increases at higher pH, temperature, and concentration of O‐acetylserine. On the other hand, sodium hydrosulfide is more soluble at a higher pH. A stirred‐tank bioreactor with a continuous substrate feed was employed to overcome this problem. The O‐acetylserine feed was stored at its saturation level (2.05M) at pH 5.0, and the sodium hydrosulfide feed was dissolved at 2.05–2.3M without pH adjustment (pH ≥ 11.5). Both substrates were simultaneously introduced into the bioreactor. The performance of the bioreactor was optimized by employing an automatic feedback control system to regulate the concentration of O‐acetylserine in the bioreactor. This feedback control system was based on the fact that as the bioconversion proceeds, protons are produced along with cysteine. A pH controller thus detected the decrease in pH and activated the substrate pumps. After mixing in the bioreactor, these two substrate solutions behaved as a base due to the high alkalinity of sodium hydrosulfide. Thus, substrate infusion started when the pH was lower than the set point, i.e., the reaction pH, and stopped when the pH was raised higher than the set point. The amount of substrate introduced was determined by the alkalinity of the mixture of the two substrates, which in turn was controlled by the concentration of sodium hydrosulfide. After optimizing the sodium hydrosulfide concentration and the substrate feed rate, the bioconversion gave a productivity of 3.6 g L‐cysteine/h/g dry cell weight S. typhimurium, an L‐cysteine titer of 83 g/L and a molar yield based on O‐acetylserine of 94%.
Theoretical and experimental studies on the influence of ultrasound on immobilized enzymes
Authors: Schmidt Peter , Rosenfeld Eike , Millner Rudolf , Czerner Regina , Schellenberger Alfred
Published: December 2004

Experimental investigations on α‐amylase and glucoamylase bound to porous polystyrene show that the activity of immobilized enzymes can be raised in the presence of an ultrasonic field. The maximum activity increase in a flow cuvette at 7.6 MHz and a sound intensity of 5 kW/m2 amounts to more than 200% under the given experimental conditions. A mathematical model based on the differential equation for the interior and exterior substrate transport is set up and solved numerically. From the theoretical considerations and the experiments it is evident that the mechanism of the ultrasonic effect can be explained in terms of a reduction of the unstirred diffusion layer around the matrix particles.
Modeling dynamic experiments on the anaerobic degradation of molasses wastewater
Authors: Denac M. , Miguel A. , Dunn I. J.
Published: December 2004

The kinetics of anaerobic degradation of a molasses wastewater were measured under constant pH conditions in a laboratory scale packed bed reactor. In continuous and batch experiments the formation and degradation rates of the organic acids (butyric, propionic and acetic) have been followed. The influence of hydrogen gas on the acid degradation rates has been measured and, contrary to the literature and the thermo‐dynamic calculations, no inhibition was detected, biofilm diffusional effects may be the reason. Two dynamic simulation models were tested, a heterogeneous model, which considered the biofilm diffusion–reaction phenomena and a quasihomogeneous model with the same kinetics. Except for hydrogen, the diffusion effects were found to be negligible. Otherwise both models gave essentially the same results and the time profiles of acids, hydrogen, carbon dioxide and methane agreed relatively well with dynamic startup experiments. Batch experiments showed the acid concentrations to be highly sensitive to the initial molasses concentration. This aspect was not included in the model but is being investigated further.
Revised enzyme synthesis rate expression in cybernetic models of bacterial growth
Authors: Turner Brian G. , Ramkrishna Doraiswami
Published: December 2004

A revised enzyme synthesis rate expression for cybernetic models of bacterial growth is presented. The rate expression, which is comprised of inducible and constitutive contributions, provides for a basal enzyme level that is necessary to predict certain types of commonly observed continuous culture transients. The response of a continuous culture to a step change in feed stream composition is simulated using both the old and new formulations, and the ramifications for the “matching‐law” formulation are discussed.
Limitation of growth rate by two complementary nutrients: Some elementary but neglected considerations
Authors: Baltzis Basil C. , Fredrickson A. G.
Published: December 2004

Experimental data in the literature show that the yield of biomass from a particular nutrient when that nutrient limits growth rate is often significantly different than the yield from the nutrient when some complementary nutrient limits growth rate. This article explores some possible consequences for bioreactor dynamics of dependence of yield coefficients on the identity of the nutrient that limits growth rate.
Theoretical study of tryptophan operon: Application in microbial technology
Authors: Sinha Somdatta
Published: December 2004

A model for the tryptophan operon is formulated based on the genetic and biophysical data available on the structure of the operon and the nature of interactions between the represser and its ligands. Studies have been done, on wild‐type, superrepressing, and loose‐binding strains to identify conditions at which the stability of the system changes (i.e., evolves to a stable synthesis or periodic synthesis with increasing amplitude). Also, the factors that increase the yield of tryptophan are studied and predictions made, based on the results, for obtaining overproducing strains of tryptophan that can be used for the industrial production of this useful amino acid.
Effect of pH on growth of mixed cultures in batch reactor
Authors: Lallai A. , Mura G. , Miliddi R. , Mastinu C.
Published: December 2004

This work has studied the effect of pH on specific growth rate μ, yield factor Y, and specific substrate consumption rate U for two mixed microbial populations (sludge A and B) in a batch reactor with a limiting substrate (phenol). The mathematical analysis of μ and U as a function of pH has been applied not only to the results of the present work but also to other published data. On the basis of the results obtained, the following remarks can be made: (a) The effect of pH on bacterial activity differed for the two sludges; (b) variations in pH of one unit more or less than optimum pH can give rise to appreciable variations in μ and U; and (c) with regard to the mixed populations used in this study, the μ or U and pH data for the range investigated can be suitably described by a parabolic relation.
A segregated model of recombinant multicopy plasmid propagation
Authors: Wittrup K. D. , Bailey J. E.
Published: December 2004

A segregated model of multicopy plasmid propagation has been formulated which incorporates plasmid replication and partition functions, as well as the effect of plasmid presence on host growth rate. Growth of plasmid‐free cells in selective medium is explicitly analyzed. The model parameters can be determined from experimentally measurable quantities. Propagation of a recombinant multicopy plasmid in the yeast Saccharomyces cerevisiae is analyzed using this model.
Elucidation of enzyme control mechanisms using macroscopic measurements in a mixed substrate fermentation system
Authors: Pih Norman , De Bernardez Eliana , Dhurjati Prasad
Published: December 2004

The objective of this work was to relate macroscopically measurable on‐line fermentation parameters such as dissolved oxygen, off‐gas oxygen and carbon dioxide, and cell mass, to the controlled production of key intracellular enzymes under carbon limited conditions. Both batch and perturbed batch aerobic fermentations were performed using two different strains of Escherichia coli, with glucose and lactose as the sole carbon sources. The two strains differed from each other only in the lac operon region of their genome. The parent strain, E. coli 3000, was inducible for the enzyme β‐galactosidase. The other strain, E. coli 3300, was a constitutive mutant in the production of β‐galactosidase. In all experiments, off‐line assays of sugars and β‐galactosidase activity were performed. It was observed that there is a clear relationship between the macroscopic on‐line measurements, dissolved oxygen tension, carbon dioxide evolution rate and oxygen uptake rate, and the microscopic control phenomena of catabolite repression, catabolite inhibition, and inducer repression.
Hydrolysis of beet pulp polysaccharides by extracts of solid‐state cultures of Pencicillium capsulatum
Authors: Considine P. J. , O'Rorke A. , Hackett T. J. , Coughlan M. P.
Published: December 2004

Extracts of solid‐state cultures of Penicillium capsulatum grown on beet pulp exhibit cellulolytic, hemicellulolytic, and pectinolytic activities. Such extracts catalyzed extensive solubilization of untreated beet pulp. The effects of pH, temperature, and endproducts on the saccharification process were investigated.
Synthesis and characterization of a water‐soluble affinity polymer for trypsin purification
Authors: Luong J. H. T. , Male K. B. , Nguyen A. L.
Published: December 2004

A specific ligand bound polymer has been synthesized for the purpose of purification and stabilization of trypsin, an easily autodigestible enzyme. The affinity polymer was formed by copolymerizing N‐acryloyl‐m‐aminobenzamidine, a strong trypsin inhibitor, and acrylamide in the absence of oxygen. Kinetic studies on the trypsin inhibition revealed that there was a strong binding between this enzyme and the polymer and the mechanism was of a competitive manner with an inhibition constant of 0.6 × 10−3M. Such an affinity polymer was also very effective in preventing trypsin from auto‐digestion at 4°C.

Based on this finding and the principle of cross flow filtration, a new process has been developed for purification of trypsin from a solution containing chymotrypsin. The experimental data indicated that trypsin was bound to the polymer (MW > 105) and remained in the retentate while unbound chymotrypsin was collected in the filtrate. This purification process has a capability of recovering 98% pure trypsin at 90% yield.
MPS: An artificially intelligent software system for the analysis and synthesis of metabolic pathways
Authors: Seressiotis Alex , Bailey James E.
Published: December 2004

The concepts of artificial intelligence have been applied for the development of a software system for metabolic pathway synthesis (MPS). An easily expandable data base system for storing enzyme and substance descriptions is used by a search algorithm for the identification of possible ways to interconvert carbon‐carrying metabolites. A versatile screening capability permits the user to identify all pathways which contain or exclude any combination of enzymes, substrates, and/or products. Information provided by MPS can be used to predict on a qualitative basis the effects of adding or deleting enzymatic activities to or from the cellular environment, to classify pathways with respect to cellular objectives, and to extract information about metabolic regulation. MPS can be used subsequently to aid the identification of appropriate genotypes or genetic modifications that will redirect metabolism towards amplified production of desirable bioproducts. Two examples illustrating the capabilities of MPS are presented. In the first example, which considers the conversion of glucose 6‐phosphate to pyruvate, MPS synthesized the classical catabolic pathways (EMP, pentose phosphate and ED) along with possible variations. A route for the biosynthesis of L‐alanine that does not incorporate the enzyme alanine aminotransferase was revealed by MPS during synthesis of alternative pathways which produce L‐alanine from pyruvate.