bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal substrate feeding policy for a fed batch fermentation with substrate and product inhibition kinetics
Authors: Hong J.
Published: May 2005

The optimal substrate feeding policy for the fed batch fermentation which is governed by product and substrate inhibited kinetics is presented. The conjunction point between nonsingular and singular arcs and the feeding policy along the singular arc are derived analytically in terms of the concentrations of substrate and product and the liquid volume. Thus, it is possible to determine the feeding rate by monitoring the state variables (i.e., closed loop control). As a specific example, an optimization study of the fed batch fermentation for ethanol production by Saccharomyces cerevisiae is presented. It is shown that the optimal feeding patterns are heavily dependent upon the initial conditions. The point selectivity provides the guideline for predicting the optimal feeding patterns and explaining the results of rigorous mathematical analysis.
Kinetic model of hydrocortisone 1‐en‐dehydrogenation by Arthrobacter globiformis
Authors: Gachok V. P. , Grytsay V. I. , Arinbasarova A. Yu. , Medentsev A. G. , Koshcheyenko K. A. , Akimenko V. K.
Published: May 2005

A kinetic model of the hydrocortisone‐to‐prednisolone transformation by Arthrobacter globiformis is constructed using the experimental data obtained in studies of this process. Besides adequately describing experimental data, the model allows one to determine the relation between hydrocortisone oxidation and the level of endogenous substrates in bacterial cells, and the relation between the saturating concentration of hydrocortisone in the enzymic system of bacteria and the content of endogenous substrates in their cells, as well as the regulation of the transmembrane potential and the activation by the uncouplers.
Combined rapid‐steam hydrolysis and organosolv pretreatment of mixed southern hardwoods
Authors: Rughani Jagdish , McGinnis Gary D.
Published: May 2005

Various types of pretreatments are used for biomass conversion of woods. The major objective of most pre treatments is to increase the susceptibility of cellulose and lignocellulose material to acid and enzymatic hydrolysis. In this study, southern mixed hardwoods were pretreated by combined rapid steam hydrolysis (RASH) and organosolv methods. It was found that the major factor in the pretreatment was the RASH temperatures. The organosolv temperature had only a minor effect on the reactivity of the final product. The enzymatic rate studies indicated that the RASH process helps in increasing the accessibility of cellulose to enzymatic hydrolysis and increased the amount of soluble lignin While the organosolv process only removed solubilized lignin. Another effect of the combined treatment was the decreasing of the enzymatic rate relative to a single RASH pretreatment. All hemicellulose is lost during these pretreatments. Three alcohols (methanol, ethanol, and butanol) were studied using a combined RASH organosolv process. At lower temperatures there were small differences between the alcohols; however, at higher temperatures all alcohols were equally effective. At longer RASH times, the percentage of glucose in the final product, as well as the amount of solubilized lignin, increased. However, the longer RASH times led to a decrease in enzymatic rates, Organosolv residence time studies of 15, 30, and 45 minutes displayed little effect on the product. Various wood‐to‐solvent ratios and water‐to‐alcohol ratios had very little effect on the yield of products. The stability of RASH treated material be fore organosolv process was studied under various storage conditions. The storage conditions had no apparent effect on the product.
General theory of determining intraparticle active immobilized enzyme distribution and rate parameters
Authors: Hossain Md. M. , Do D. D.
Published: May 2005

A general theory is presented in this article for determining the intrinsic rate constants for the main reaction and deactivation reaction, the effective diffusivity of the substrate, and the active enzyme distribution within porous solid supports from deactivation study of a continuous stirred‐basket reactor (CSBR). For the parallel deactivation five reaction kinetics are considered: (a) Michaelis–Menten, (b) substrate inhibition, (c) product inhibition (competitive), (d) product inhibition (anticompetitive), and (e) zero‐order kinetics. The experimental results of the system of hydrogen‐peroxide‐immobilized catalase on controlled‐pore glass particles are analyzed to demonstrate the application of the theory developed for parallel deactivation of active immobilized enzyme (IME). For series deactivation only first‐order kinetics is treated, and a numerical procedure is proposed to deter mine the rate parameters and the internal active enzyme distribution. The experimental data of the system of glucose‐immobilized glucose oxidase on silica‐alumina and controlled‐pore glass particles are used to verify the theory.
Plasmid stability and α‐amylase production in batch and continuous cultures of Bacillus subtilis TN106[pAT5]
Authors: Wei Daniel , Parulekar Satish J. , Stark Benjamin C. , Weigand William A.
Published: May 2005

Cell growth and enzyme (α‐amylase) production characteristics of Bacillus subtilis TN106 containing the recombinant plasmid pAT5 are investigated in batch and continuous cultures using a defined medium with glucose as the limiting nutrient. The batch culture studies demonstrate that the recombinant plasmid, reported earlier1 to be stably maintained in the host, suffers from segregational and structural instabilities. The structural instability of this strain occurred during culture storage and can be eliminated in bioreactor experiments by using a modified inoculum preparation procedure. Such elimination allows an unbiased investigation of segregational instability via continuous culture studies. Such studies conducted with this fast growing microorganism, in the absence of antibiotic selection pressure, indicate a very efficient glucose utilization (very low residual glucose concentrations) over a wide range of dilution rates (0.16 h−1 – 0.94 h−1). The nearly time–invariant and low residual glucose concentrations at each such dilution rate enable convenient estimation of growth parameters of the host and recombinant cells and frequency of segregational instability from transients in the resulting mixed cultures. The specific α‐amylase activity exhibits an inverse relationship to the specific growth rate of recombinant cells. The growth of recombinant cells is not affected by the presence of antibiotic (kanamycin). The growth advantage of host cells over recombinant cells diminishes with increasing dilution rate.
Effects of reactant heterogeneity and mixing on catabolite repression in cultures of Saccharomyces cerevisiae
Authors: Fowler J. D. , Dunlop E. H.
Published: May 2005

An experimental study was conducted into the effect of reactant heterogeneity on glucose‐fed continuous cultures of S. cerevisiae, The heterogeneity was altered by varying mixing intensity in the nutrient entry region within a static mixing device. Experimental results confirm simulation predictions based upon a simple growth model, showing that mixing in the entry region can govern macroscopic culture behavior. Specifically, at high dilution rates, the biomass concentration was reduced by mixing patterns that increased the size of regions where glucose exceeded the threshold for catabolite repression. Because the size of such repressive regions is not uniquely determined by reactant segregation, the authors argue that in biological systems (and others involving a threshold response) an alternative measure of mixing quality should be used. Conclusions are drawn concerning the simulation of biological reactors for design purposes, and the importance of nutrient delivery systems to reactor performance.
Membranes and bioreactors: A technical challenge in biotechnology
Authors: Belfort Georges
Published: May 2005

Integrating the properties of synthetic membranes with biological catalysts such as cells and enzymes forms the basis of an exciting new technology called membrane bioreactors. The impetus behind this marriage comes from the recent spectacular advances in recombinant DMA and cell fusion technologies and the need to develop competitive bioprocessing schemes to produce complex and active biological molecules. The advantages and limitations of using membrane bioreactors for entrapping whole cells and enzymes are reviewed. Various membrane configurations such as microcapsules, hollow fibers, and flat sheets are compared. Several different entrapped membrane bioreactors, including single, laminated and microporous, for the conversion of optically active enantiomers are described. As with new and exciting technologies, the future of membrane bioreactors in biotechnology will depend on their ability to produce desired molecules at competitive costs.
FIA for on‐line monitoring of important lactic acid fermentation variables
Authors: Nielsen J. , Nikolajsen K. , Villadsen J.
Published: May 2005

An automated system with semi on‐line monitoring of glucose, lactic acid, protein, and optical density during lactic acid fermentations, is set up to study the dynamics of lactic acid bacteria. The analyzers for glucose, lactic acid, and protein are based on flow injection analysis (FIA). The system consists of a laboratory fermentor with a continuous withdrawal system and an analysis system where glucose, lactic acid, and protein concentration are measured together with the optical density of the fermentor sample. The system is controlled by a personal computer.

The system response is fast, and it yields a large number of reliable and precise analytical data, whoch is of great importance for mathematical model building. Some premliminary results are shown.
Oscillations in continuous cultures of microorganisms: Criteria of utility of mathematical models
Authors: Ivanitskaya J. G. , Petrikevich S. B. , Bazykin A. D.
Published: May 2005

This article proposes a new approach to the modeling of continuous cultures of microorganisms based on the concept of universality classes. Instead of analysis of concrete sets of equations, vast classes including models with identical qualitative features should be studied. The class of models of the second order is the simplest one, and it is analyzed in order to demonstrate the mathematical methods used. The authors have shown that the simplest model usually used for the description of continuous cultures is sensitive to even slight modifications. The modified model changes its properties and gives rise to a class of models that are applicable to the description of damped and nondamped oscillations of biomass and substrate concentrations in a fermenter. Irrespective of the mode of the initial model modification, the oscillations have a number of common features. These features can be used as the criteria of utility of this class of models for simulation of culture behavior. Two models of the class in question (with nonzero maintenance coefficient and nonconstant yield) are analyzed using these criteria.
Kinetics of acetate, propionate and butyrate removal in the treatment of a semi‐synthetic landfill leachate on anaerobic filter
Authors: Gourdon R. , Comel C. , Vermande P. , Véron J.
Published: May 2005

The kinetics of acetate, propionate, and butyrate removal was studied in conditions of leachate treatment in a plug flow anaerobic fixed‐film reactor made of a sequence of seven perfectly mixed compartments. An original experimental procedure was followed under sequential feeding conditions so as to maintain the Bacteriol biomass in a quasi‐steady state all along the study. With an appropriate computer program based on the least squares method, the apparent kinetic parameters of VFA removal were calculated within concentration ranges below the levels of salt inhibition. The models proposed are based on simple theoretical considerations. For acetate and n‐butyrate removal, the best fits were given by the Michaelis‐Menten equation with respectively: V = 0.49 ± 0.06 g CH3 COOH g−1 biomass h−1and 0.18 ± 0.02 g n‐CH3CH2CH2COOH g−1 biomass h−1 and: Ks = 21.2 ± 0.9 g CH3COOH L−1 liquid phase and 8.2 ± 0.9 g n‐CH3CH2CH2COOH L−1 liquid phase, Iso‐butyrate was produced during n‐butyrate catabolism and the apparent removal rate of (n + iso)‐butyrate considered as a whole was also described by the Michaelis‐Menten equation with V = 0.14 ± 0.02 g(n + iso)‐butyrate g−1 biomass h−1 and Ks = 9.0 ± 1.2 g (n + iso) butyrate L−1 liquid phase. On the other hand in the case of propionate, the best fit was obtained with a first‐order equation with Kspec = (0.88 ± 0.05) 10−2 L liquid phase g−1 biomass h−1. These constants were subsequently used to predict the removal of mixtures of the three major VFAs under study, at various feed concentrations. Three sets of concentrations were tested, and the experimental data were compared to the simulations. This study, together with other experimental observations previously reported, tends to show that under sequential feeding conditions the classical assumption of butyrate β‐oxidation should be rejected. Butyrate seems to be anaerobically decarboxylated, but propionate thus formed inside the biofilm is degraded as soon as its formation proceeds. It was therefore considered that butyrate degradation produces, through propionate intermediate, 1 mole acetate per mole butyrate removed. When propionate or butyrate concentrations were high, the same phenomenon was noted, to a much lower extent, for the degradation of acetate formed inside the biofilm.
Production of human immune interferon by recombinant mammalian cells cultivated on microcarriers
Authors: Smiley A. L. , Hu W‐S. , Wang D. I. C.
Published: May 2005

Recombinant Chinese hamster ovary (rCHO) cells were cultivated on microcarriers for the production of human immune (Gamma) interferon. The effect of basal medium, serum, and microcarrier concentration on interferon production was investigated. The specific interferon productivity in the post‐confluent stage was similar to that in the growth stage. Control of the pH results in a significant improvement in the volumetric interferon production. The volumetric production rate of interferon by these rCHO cells did not decrease after one month of cultivation on microcarriers.
The heat generated by yeast cultures with a mixed metabolism in the transition between respiration and fermentation
Authors: von Stockar U. , Birou B.
Published: May 2005

The heat generated by both batch and continuous cultures of the yeast K. fragilis was studied using a modified Bench Scale Calorimeter. Batch cultures were used to measure the heat dissipation rates and the heat yields during fully aerobic and completely anaerobic growth, whereas continuous cultures enabled, in addition, a quantitative study of heat dissipation rates during growth on mixed metabolism. In this case, the extent of fermentation versus respiration could be specified and controlled by varying the degree of oxygen limitation. The heat dissipated per unit biomass formed was highest for fully respirative catabolism and fell continuously to a much lower value typical of anaerobic cultures as the catabolism was shifted increasingly to the fermentative mode. The heat generated per mole of oxygen taken up stayed quite close to the fully aerobic value of 506 kJ mol−1 even when a sizable fraction of the substrate available to catabolism was fermented. If the fraction of respiration in the metabolism is lowered beyond a certain threshold, the ratio of the heat generation to oxygen consumption starts to increase dramatically and finally tends to infinity for fully anaerobic growth. All experimental results were quantitatively analyzed and explained on the basis of a simple model which formally describes the cultures in terms of two parallel “chemical” reactions. In simple cases such as the one presented here, the model enables calculation of the whole stoichiometry of the culture from a single measured heat yield.
A simulation study of a continuous two‐phase dry digestion system
Authors: Mata‐Alvarez Joan
Published: May 2005

In this article a two‐phase system for the continuous digestion of wastes with a high solid content is simulated. The studied parameters are: (1) Recirculation from the methanizer to the hydrolyzer, (2) methanizer/hydrolyzer volume ratio, and (3) hydraulic retention time in the hydrolyzer (HRT). Results show that the recirculation ratio is an important operational factor with a large influence on the biodegradation yield, especially at low HRT. Optimum levels of this parameter are established. Some runs of the program have been carried out to test the stability of the system. This has proved to be very stable, especially at low recirculation ratios. The results also show that volume ratio does not appreciably affect the performance of the system, provided it is over a critical value, dictated by the allowable methanizer load.
NADH and flavin fluorescence responses of starved yeast cultures to substrate additions
Authors: Siano S. A. , Mutharasan R.
Published: May 2005

Model experiments were performed with starved yeast (Saccharomyces cerevisiae) cultures in a batch reactor in order to develop a better understanding of NAD(P)H and flavin culture fluorescence. Fluorescence was monitored during aerobic–anaerobic–aerobic transitions and ethanol and glucose substrate addition experiments. Interpretations of the fluorescence responses obtained are provided, with consideration given to redox compartmentation and the formation of ethanol shortly after a glucose addition. An analytical spectrofluorophotometer was interfaced to a personal computer and adapted to measure fluorescence in a bioreactor. This was achieved by the use of quartz fiber‐optic waveguides to convert the right‐angle cuvette geometry of the analytical spectrofluorophotometer to an open‐ended fluorescence probe geometry, resulting in a flexible culture fluorescence apparatus. Features of the apparatus include variable excitation and emission wavelengths, allowing for detection of NAD(P)H or flavin fluorescence, as well as small slit widths, a variable sampling rate, excitation and emission scanning capabilities, and good sensitivity.
Kinetics of the hydrolysis of di‐ and trisaccharides with Aspergillus niger glucoamylases I and II
Authors: Meagher Michael M. , Reilly Peter J.
Published: May 2005

Near‐homogeneous forms of glucoamylases I and II, previously purified from an industrial Aspergillus niger preparation, were used to hydrolyze a number of di‐ and trisaccharides linked by α‐D‐glucosidic bonds. Maximum rates and Michaelis constants were obtained at various temperatures and pH values with glucoamylase I for the disaccharides β,α‐trehalose, kojibiose, nigerose, maltose, and isomaltose and the trisaccharides panose and iso‐maltotriose, and with glucoamylase II for maltose, maltotriose, and isomaltotriose. Maximum rates were highest and energies of activation were lowest for maltose, maltotriose, and panose, the only three substrates containing α‐D‐(1, 4)‐glucosidic bonds. Michaelis constants were lowest and standard heats of binding were most negative for maltose and maltotriose. The variation of maximum rates and Michaelis constants with varying pH values suggested that two carboxyl groups were involved in substrate binding.
A mathematical description of recombinant yeast
Authors: Coppella Steven J. , Dhurjati Prasad
Published: May 2005

A model was formulated to examine specific experimental data of growth and heterologous product formation with recombinant Saccharomyces cerevisiae while incorporating available literature. The model simulated dry cell weight, glucose, ethanol, dissolved oxygen, human Epidermal Growth Factor (hEGF) production, fraction of recombinant cells, oxygen uptake rate, and carbon dioxide production rate for batch, fed batch, and hollow fiber bioreactor configurations. Nineteen differential equations, 24 analytical equations, and 48 parameters were required. Due to the lack of detailed studies needed for the ADH‐II and the TCA enzyme pool, 8 of the 48 parameters were adjustable. Simulation results are presented for verification of the model which successfully described the observed phenomena for the fermentations of S. cerevisiae strain AB103. 1 pYαEF‐25. Also presented is a statistical analysis of the model's fit and model parameter sensitivity.
Vancomycin partitioning in aqueous two‐phase systems: Effects of pH, salts, and an affinity ligand
Authors: Lee Cheng‐Kang , Sandler Stanley I.
Published: May 2005

The partitioning of vancomycin in polyethylene glycol (PEG)‐dextran and PEG‐phosphate aqueous two‐phase systems was studied at different pHs, at varying concentrations of neutral salts, and with an affinity ligand attached to methoxy polyethylene glycol (MPEG). Vancomycin is found to partition preferentially into the PEG‐rich top phase, and its partition coefficient increases nearly exponentially with the addition of water structure‐making salts, such as sodium sulfate and sodium chloride, but is independent of sodium phosphate concentration. In the PEG‐dextran system the vancomycin partition coefficient increases 3‐fold in acidic and neutral solutions, while in the PEG‐phosphate system it increases about 30‐fold on the addition of the same amount of sodium chloride (1. 5 mol/kg). In basic solution, above its isoelectric point, the vancomycin partition coefficient increases slightly with NaCI concentration in the PEG‐dextran system. We also examined the use of the dipeptide D‐ala‐D‐ala as an affinity ligand on MPEG to extract vancomycin into the PEG‐rich phase. The vancomycin partition coefficient increased almost 7‐fold upon adding the MPEG‐ligand in an amount equal to approximately 3% of the total PEG in the system. Finally, fractionation of the polydisperse phase‐forming polymers in the two‐phase PEG‐dextran system was observed. The effect of this polymer fractionation on the partition coefficient of vancomycin is discussed.
Effects of temperature on cell growth and xanthan production in batch cultures of Xanthomonas campestris
Authors: Shu Chin‐Hang , Yang Shang‐Tian
Published: May 2005

Batch xanthan fermentations by Xanthomonas campestris NRRL B‐1459 at various temperatures ranging between 22°C and 35°C were studied. At 24°C or lower, xanthan formation lagged significantly behind cell growth, resembling typical secondary metabolism. However, at 27°C and higher, xanthan biosynthesis followed cell growth from the beginning of the exponential phase and continued into the stationary phase. Cell growth at 35°C was very slow; the specific growth rate was near zero. The specific growth rate had a maximum value of 0.26 h−1 at temperatures between 27°C and 31°C. Cell yield decreased from 0.53 g/g glucose at 22°C to 0.28 g/g glucose at 33°C, whereas xanthan yield increased from 54% at 22°C to 90% at 33°C. The specific xanthan formation rate also increased with increasing temperature. The pyruvate content of xanthan produced at various temperatures ranged between 1.9% and 4.5%, with the maximum occurring between 27°C and 30°C. These results suggest that the optimal temperatures for cell growth are between 24°C and 27°C, whereas those for xanthan formation are between 30°C and 33°C. For single‐stage batch fermentation, the optimal temperature for xanthan fermentation is thus dependent on the design criteria (i. e., fermentation rate, xanthan yield, and gum qualities). However, a two‐stage fermentation process with temperature shift‐up from 27°C to 32°C is suggested to optimize both cell growth and xanthan formation, respectively, at each stage, and thus to improve overall xanthan fermentation.
An ESR study of spin‐labeled silk fibroin membranes and spin‐labeled glucose oxidase immobilized in silk fibroin membranes
Authors: Asakura Tetsuo , Yoshimizu Hiroaki , Kakizaki Mitsuhiro
Published: May 2005

This article describes the characteristics of silk fibroin membranes and glucose oxidase, immobilized in membranes as determined by a variety of physical methods, mainly the spin‐label electron spin resonance (ESR) method. The properties of membranes insolubilized by different methods, i. e., immersion in 80% methanol aqueous solution, uniaxially drawing by placing on a stretcher, and hydration by placing in a desiccator of 96% relative humidity (RH) for 17 h, are compared. The results are also analyzed in relation to ESR spectra of spin‐labeled immobilized glucose oxidase and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy as a model of the substrate. It is concluded that the heterogeneous structures of the swollen membranes in water differ locally among membranes insolubilized by different methods, but the immobilized state of the enzyme in such membranes is mostly similar. This is correlated to the fact that the thermal or pH stabilities are essentially same among glucose‐oxidase‐immobilized silk fibroin membranes insolubilized by different methods.
Protease immobilization onto polyacrolein microspheres
Authors: Hayashi Toshio , Ikada Yoshito
Published: May 2005

Water‐insoluble proteases were prepared by immobilizing papain and chymotrypsin onto the surface of polyacrolein microspheres with and without oligoglycines as spacer. The activity of immobilized proteases was found to be still high toward small ester substrates, but very low toward casein, a high‐molecular‐weight substrate. The relative activity of the immobilized proteases without spacer decreased gradually with the decreasing surface concentration of the immobilized proteases on the microspheres. On the contrary, the immobilized proteases with oligoglycine spacers gave an almost constant activity for the substrate hydrolysis within the surface concentration region studied and gave a much higher relative activity than those without any spacer. With the longer spacer, the immobilized enzymes showed a higher activity toward casein hydrolysis, whereas there was an optimum length for the spacer when hydrolysis was carried out toward the low‐molecular‐weight substrate. The thermal stability of the immobilized proteases was higher than that of the respective native proteases. The initial enzymatic activity of the immobilized proteases maintained almost unchanged without any elimination and inactivation of proteases, when the batch enzyme reaction was performed repeatedly, indicating the excellent durability.
Microbial control of the production of hydrogen sulfide by sulfate‐reducing bacteria
Authors: Montgomery Anne D. , Mclnerney Michael J. , Sublette Kerry L.
Published: May 2005

A sulfide‐resistant ctrain of Thiobacillus denitrificans, strain F, prevented the accumulation of sulfide by Desulfovibrio desulfuricans when both organisms were grown in liquid medium or in Berea sandstone cores. The wild‐type strain of T. denitrificans did not prevent the accumulation of sulfide produced by D. desulfuricans. Strain F also prevented the accumulation of sulfide by a mixed population of sulfate‐reducing bacteria enriched from an oil field brine. Fermentation balances showed that strain F stoichiometrically oxidized the sulfide produced by D. desulfuricans and the oil field brine enrichment to sulfate. These data suggest that strain F would be effective in controlling sulfide production in oil reservoirs and other environments.
Development of bioreactors for the culture of surface immobilized plant cells
Authors: Archambault J. , Volesky B. , Kurz W. G. W.
Published: May 2005

The scaleup of the technique of plant cell surface immobilization was performed successfully in specifically designed laboratory size bioreactors. The immobilizing matrix was formed into a vertically wound spiral providing for a high immobilizing area‐to‐volume ratio (0.8–1.2 cm−1). A modified airlift and a mechanically stirred vessel delivered a best bioreactor performance characterized by low biomass frothing and highly efficient plant cell attachment and retention (≥96%). The growth of Catharanthus roseus cells investigated in these bioreactors was found not to be mass transfer limited. It required mild mixing and aeration levels (kLa ∼ 10–15 h−1). The biomass formation pattern of surface immobilized plant cells generally exhibited a linear growth phase followed by a stationary phase characterized by the presence of residual carbohydrates in the medium, contrary to suspension cultures. This behavior was found to depend on the plant cell type and/or line cultured, as well as on the inoculum age. The space restriction and unidirectional growth of the SIPC biofilm combined with the limited availability of essential intracellular nutrients rapidly accumulated from the medium by the stationary phase inoculated plant cells all likely contributed to the culture behavior.
Simple constrained‐optimization view of acetate overflow in E. coli
Authors: Majewski R. A. , Domach M. M.
Published: May 2005

The production of acetate by aerobically growing E. coli is examined. The problem is formulated in terms of a flow network that has as its objective maximal ATP synthesis. It is found that when loads are imposed and flux constraints exist either at the level of NADH turnover rate or the activity of a key Krebs cycle enzyme, switching to acetate overflow is predicted. Moreover, the result found for the latter constraint can be shown to be formally equivalent to a correlation experimentally determined for the specific rate of acetate production by E. coli K‐12.
On performing experimental studies on transient states of continuous‐flow methanogenic reactors
Authors: DeLorme Allan J. , Kapuscinski Richard B.
Published: May 2005

One approach to exploring the behavior of microbial cultures during transient conditions of unbalanced growth is to experimentally observe continuous‐flow biological reactors which have been subjected to perturbations in the influent flowrate and/or concentration of growth‐limiting substrate. Proper interpretation of such experiments requires that appropriate account be taken of reaction stoichiometry, the distribution and abundance of microbial populations within the reactor, and the nonideality of mixing and flow distribution in the reactor. These aspects of proper experimental design are particularly critical when the system of interest involves methanogenic consortia and is not a completely‐mixed, suspended‐growth reactor.
Production of emulsan in a fermentation process using soybean oil (SBO) in a carbon–nitrogen coordinated feed
Authors: Shabtai Yossef , Wang Daniel I. C.
Published: May 2005

A fermentation process for the microbial production of an amphipatic lipopolysaccharide, emulsan, has been established using a triglyceride carbon source in a coordinated carbon–nitrogen feed strategy. The polysaccharide was produced by the Acinetobacter strain at a productivity of about 0.5 g emulsan/L h while utilizing only the fatty acids (FA) portion of the triglycerides or free fatty acids that were fed into the medium.

A useful correlation between the utilization of the fatty acids and the consumption of the nitrogen was found and employed for the practical feed strategy using an appropriate CN ratio (7.7 g C/g N) of the soybeanoil (SBO) (carbon source) to the ammonium hydroxide base (nitrogen source). Either the pH control or the supervising computer system could accomplish the adequate balanced feed in to the fermentor. Lipolysis slowdown was overcome by switching from a triglyceride carbon source to a free fatty acids one. A yield of about 0.2 g emulsan/g fatty acids was obtained and a final concentration of over 20 g/L was reached. The polymeric product was found to be partially associated with the cell‐oil complexes in the fermentation broth unless the oily carbon source was efficiently exhausted. A fedbatch fermentation that employed a shift of the carbon source feed from triglycerides to free fatty acids appeared to be an appropriate and feasible way of producing the polymer.
Heat transfer simulation in solid substrate fermentation
Authors: Saucedo‐Castañeda G. , Gutiérrez‐Rojas M. , Bacquet G. , Raimbault M. , Viniegra‐González G.
Published: May 2005

A mathematical model was developed and tested to simulate the generation and transfer of heat in solid substrate fermentation (SSF). The experimental studies were realized in a 1‐L static bioreactor packed with cassava wet meal and inoculated with Aspergillus niger. A simplified pseudohomogeneous monodimensional dynamic model was used for the energy balance. Kinetic equations taking into account biomass formation (logistic), sugar consumption (with maintenance), and carbon dioxide formation were used. Model verification was achieved by comparison of calculated and experimental temperatures. Heat transfer was evaluated by the estimation of Biot and Peclet heat dimensionless numbers 5–10 and 2550–2750, respectively. It was shown that conduction through the fermentation fixed bed was the main heat transfer resistance. This model intends to reach a better understanding of transport phenomena in SSF, a fact which could be used to evaluate various alternatives for temperature control of SSF, i.e., changing air flow rates and increasing water content. Dimensionless numbers could be used as scale‐up criteria of large fermentors, since in those ratios are described the operating conditions, geometry, and size of the bioreactor. It could lead to improved solid reactor systems. The model can be used as a basis for automatic control of SSF for the production of valuable metabolites in static fermentors.
A mathematical model for the growth of mycelial fungi in submerged culture
Authors: Aynsley M. , Ward A. C. , Wright A. R.
Published: May 2005

A new kinetic model is developed which provides a simple quantitative description of the growth of mycelial organisms. The main concept of this model is that the fungal hypha can be regarded as a form of self‐extending tubular reactor. Nutrients are absorbed along the length of the “reactor,” converted into cell envelope precursors and transported forward to the growth tip where they become consumed in the process of extension; Michaelis–Menten kinetics are assumed to operate at this point. The model is capable of predicting changes in the rates of hyphal extension, branching, and fragmentation during mycelial growth in submerged culture and consequently variations in the hyphal growth unit. Simulation studies using the model are presented and the results are evaluated with reference to data from an industrial‐type fed‐batch penicillin fermentation.
Analysis of pBR322 replication kinetics and its dependency on growth rate
Authors: Kim Byung Gee , Shuler M. L.
Published: May 2005

Accurate estimates of plasmid copy number in a cell are a prerequisite for predicting plasmid stability and protein production. A refined version of a structured model for the pBR322 plasmid replication mechanism is described. The model is capable of accurately predicting pBR322 plasmid copy number in Escherichia coli B/r for a wide range of growth rates. The refinements include better estimates of promoter strength, the degradation rate of RNA species, binding constant of RNAI–RNAII reaction, and dependency of promoter strength on growth rate. The predictions of the model are verified by recent experimental observations but differ from some previous reports. This model can also be used to predict the binding constant of the RNAI–RNAII reaction of ColE1 type plasmids. At 37°C, the binding constant is estimated to be 77 ± 11 × 10−13 mL/molecule‐h for pBR322.
Product deactivation in recombinant Streptomyces
Authors: Gardner Alan R. , Cadman T. W.
Published: May 2005

The production of tyrosinase by Streptomyces antibioticus (p1J7O2) was investigated as a model system for recombinant protein production by Streptomyces. Product deactivation was found to have a severe effect on the levels of tyrosinase obtained. Tyrosinase deactivation was detected during all phases of batch cultures, with higher specific deactivation rates observed during the stationary phase. The specific deactivation rate exhibited an Arrhenius dependence on temperature, with approximately a twofold increase in the deactivation rate between 25°C and 30°C. The effect of deactivation on the determination of tyrosinase production kinetics is discussed. A strategy was implemented to increase tyrosinase productivity by enriching the growth medium and reducing the culture temperature during the period of maximum tyrosinase production. This strategy resulted in a shorter culture time and a 2.5‐fold increase in tyrosinase activity compared to a culture grown at 25°C using a standard growth medium.
Involvement of a cell size control mechanism in the induction and maintenance of oscillations in continuous cultures of budding yeast
Authors: Martegani Enzo , Porro Danilo , Ranzi Bianca Maria , Alberghina Lilia
Published: May 2005

Spontaneous oscillations occur in glucose‐limited continuous cultures of Saccharomyces cerevisiae under aerobic conditions. The oscillatory behavior is detectable as a periodic change of many bioparameters such as dissolved oxygen, ethanol production, biomass concentration, as well as cellular content of storage carbohydrates and is associated to a marked synchronization of the yeast population. These oscillations may be related to a periodic accumulation of ethanol produced by yeast in the culture medium.

The addition of ethanol to oscillating yeast cultures supports this hypothesis: indeed, no effect was observed if ethanol was added when already present in the medium, while a marked phase oscillation shift was obtained when ethanol was added at any other time. Moreover, the addition of ethanol to a nonoscillating culture triggers new oscillations. An accurate analysis performed at the level of nonoscillating yeast populations perturbed by addition of ethanol showed that both the growth rate and the protein content required for cell division increased in the presence of mixed substrate (i.e., ethanol plus limiting glucose). A marked synchronization of the yeast population occurred when the added ethanol was exhausted and the culture resumed growth only on limiting glucose. A decrease of protein content required for cell division was also apparent. These experimental findings support a new model for spontaneous oscillations in yeast cultures in which the alternative growth on limiting glucose and limiting glucose plus ethanol modifies the critical protein content required for cell division.
Enhanced shikonin production from Lithospermum erythrorhizon by in situ extraction and calcium alginate immobilization
Authors: Kim Dong Jin , Chang Ho Nam
Published: May 2005

Plant cell cultures of Lithospermum erythrorhizon were carried out to produce shikonin by in situ extraction and cell immobilization in calcium alginate bead in shake flask cultures. In situ product extraction and cell immobilization enhanced shikonin production and facilitated product recovery. In situ extraction by n‐hexadecane and cell immobilization by calcium alginate gave higher specific shikonin productivities of 7.4 and 2.5 times, respectively, than those from the cultures of free cells without extraction. Simultaneous use of both techniques increased specific and volumetric productivities of shikonin 25‐ and 15‐fold, respectively. In calcium alginate immobilized cell cultures, n‐hexadecane addition at an early stage (before 15 days) was effective for shikonin production, and solvent addition after 15 days of the culture significantly reduced shikonin production. Higher numbers of plant cell immobilized bead inoculation did not increase shikonin production and sucrose consumption. Most of the produced shikonin was dissolved in the solvent layer.
Theoretical development and performance evaluation for extractive fermentation using multiple extractants
Authors: Shi Zhongping , Shimizu Kazuyuki , Iijima Shinji , Morisue Toshiya , Kobayashi Takeshi
Published: May 2005

Mathematical formulation was made for the performance evaluation of extractive fermentation using multiple solvents. Two types of solvent‐supplying strategies were considered. One is to add multiple solvents simultaneously and the product is removed at one time. Another is to add them one by one consecutively. Computer simulation was made for batch, fed‐batch, and repeated fed‐batch operation of acetone–butanol fermentation to show the power of the approach. The result shows that the significant performance improvement in terms of the productivity and the product concentration is expected when two extractants such as oleyl alcohol and benzyl benzoate are used as compared with the case of using only one solvent.
Transient shear stresses on a suspension cell in turbulence
Authors: Cherry Robert S. , Kwon Kei‐Young
Published: May 2005

A model flow field representative of Kolmogorov eddies in turbulence is proposed, and its two parameters are expressed in terms of the known bioreactor variables ε, the rate of turbulent power dissipation, and ν, the fluid kinematic viscosity. The trajectory through this flow field of a small sphere representing a cell is determined, and from that the time‐varying local shear rate can be found. This allows calculation of the shear stress at any point on the sphere's surface as it rotates in and moves through the model eddy. The maximum shear stress imposed on the cell by the surrounding turbulence has a range of 0.5–5 dyn/cm2, and can be estimated by 5.33ρ(εν)1/2. The shear stress has two major frequency components with ranges of 1–4 and 20–80 s−1; the higher frequency component is estimated by 0.678(ε/ν)1/2. The rotation of the direction of the shear stress vector at each point on the cell's surface is also discussed. Two ways in which external stresses might affect cell growth are proposed.
Optimization of a pellicular biocatalyst for penicillin G production by Penicillium chrysogenum
Authors: Flanagan William P. , Klei Herbert E. , Sundstrom Donald W. , Lawton Carl W.
Published: May 2005

A previously developed immobilization technique involving latex coatings on solid particulate supports was investigated further for penicillin G production by Penicillium chrysogenum. Several modifications were found to decrease the germination lag time, including a higher spore concentration, a thinner latex layer, an increased latex porosity, and a decreased drying time. This approach enabled the development of immobilized mycelial pellets within 2–3 days from the onset of biocatalyst preparation and incubation.

A continuous immobilized‐cell airlift bioreactor produced penicillin G in a series of runs in which the production phase lasted up to 30 days. The productivity of this system was 3–6 times greater than the productivity of the corresponding free‐cell shake flask fermentation.
Continuous hydrolysis of oil by immobilized lipase in a countercurrent reactor
Authors: Kosugi Yoshitsugu , Tanaka Hideoki , Tomizuka Noboru
Published: May 2005

Lipase from Pseudomonas fluorescens biotype I was immobilized by adsorption of anion exchange resin using glutaraldehyde to enhance the adsorption. The activity yield of the immobilized lipase was very low (below 1%) when lipase activity was measured using emulsion substrate. The activity yield was 10–70% when lipase activity was measured using non‐emulsion substrate. Countercurrent reactors for hydrolysis of oil using non‐emulsion substrate were studied. A fluidized bed reactor was found to be superior to a fixed bed one since in a fixed bed reactor the separation rate of the two layers was slow and the flow rate of the reactor had to be slower than the separation rate. A fluidized bed reactor system equipped with settling compartments and stirring compartments was devised. Continuous lipolysis at 60 °C and continuous separation of oily product and water soluble product were performed. After continuous operation for more than 3 months, 70% of the initial activity of the immobilized lipase was observed at the end of the reaction.
Deactivation of catalase by hydrogen peroxide
Authors: Vasudevan P. T. , Weiland R. H.
Published: May 2005

When a mechanism is used to determine possible deactivation kinetics, a certain consistency with the kinetics of the main reaction is found. This result is examined in the light of experimental evidence obtained with bovine liver and Aspergillus catalases.
Continuous production of maltotetraose using a dual immobilized enzyme system of maltotetraose‐forming amylase and pullulanase
Authors: Kimura Takashi , Ogata Masafumi , Kobayashi Haruto , Yoshida Masahiro , Oishi Kayoko , Nakakuki Teruo
Published: May 2005

In order to produce a product with a high content of maltotetraose, dual‐enzyme systems composed of immobilized maltotetraose‐forming amylase (G4‐forming amylase) and pullulanase were studied. The thermostability of individually immobilized enzymes was examined in continuous operation; studies revealed that the enzyme immobilized on “Chitopearl” was much more stable than that immobilized on Diaion HP‐50. The effects of operating conditions on the stability of G4 forming amylase immobilized on “Chitopearl” were examined to confirm that the apparent half‐life data could be arranged using the immobilized enzyme stability factor, fs. As for the dual immobilized enzyme system, six methods of usage were considered, with five yielding a 7–10% (w/w) higher content of maltotetraose product than the single‐enzyme system. The effects of operating conditions on the maltotetraose production reaction were examined to confirm that the maltotetraose content of the products could be analyzed using the specific space velocity,SSV. In dual immobilized enzyme systems, pullulanase immobilized on the same carrier as the G4‐forming amylase was found to be more stable than pullulanase immobilized on separate carriers. The effectiveness of using immobilized pullulanase along with the G4‐forming amylase was confirmed from constant‐conversion operations in which the maltotetraose content in the product was kept at 50% (w/w) in laboratory‐scale experimentation.
The process utility of thermotolerant methylotrophic bacteria: I. An evaluation in chemostat culture
Authors: Al‐Awadhi Nader , Egli Thomas , Hamer Geoffrey , Mason C. Anthony
Published: May 2005

In Part l, the process utility of a thermotolerant methylotrophic bacterium is evaluated in chemostat culture under conditions where methanol, methanol/formaldehyde mixtures and dual methanol/ammonia limitation occurred. The results show that the bacterium studied was nonfastideous under steady‐state operation, in contrast to results obtained in batch culture. For application in industrial wastewater treatment processes the bacterium should be employed in systems where the biomass residence time exceeds 5 h, i. e., dilution rates < O.2 h−1. Under such conditions, methanol was essentially exhausted and the biomass yield coefficient was lowered.
Cell cycle‐ and growth phase‐dependent variations in size distribution, antibody productivity, and oxygen demand in hybridoma cultures
Authors: Ramirez Octavio T. , Mutharasan R.
Published: May 2005

Simultaneous determination of cell size and DNA content of hybridomas (HB‐32) revealed a direct correlation between average cell volume and progression through the cell cycle. Pseudocontinuous experiments showed that G1 cells, as estimated from cell size measurements, secreted monoclonal antibody at rates higher than those of cells in other stages of interphase and mitosis. Similarly, fed‐batch and batch experiments suggested that specific oxygen uptake rate (qO2) is also a function of cell cycle, being minimum for cells in G0 and G1 phase. In batch cultures, HB‐32 showed a rapid decrease in oxygen uptake rate (OUR) just prior to reaching maximum cell concentration. The OUR steadily increased from 0.01–0.05 to 0.5–0.7 mmol O2/L h as the cells went from the lag to the midexponential phase. The qO2 increased from 0.3 × 10−10−0.9 × 10−10 mmol O2/cell h at inoculation to 3.3 × 10−10−3.7 × 10−10 mmol O2/cell h during the early exponential phase where it remained relatively constant. Several hours before maximum cell concentration was reached, OUR and qO2 rapidly decreased to levels below those observed at inoculation. The time at which the shift in OUR and qO2 occurred and the onset of decrease in the average cell size corresponded to the time of glutamine depletion. Based on monitoring OUR on‐line in batch cultures, glutamine was supplemented, resulting in increased cell concentration, extension of culture viability, and increased MAb concentration.