bluuebunny/crossref_metadata_2025 huggingface dataset:
Fermentation of cellodextrins to ethanol using mixed‐culture fermentations
Authors: Freer S. N. , Wing R. E.
Published: December 2004

The potential for enhancing ethanol production from cellodextrins by employing mixed‐culture (Candida wickerhamii–Saccharomyces cerevisiae) fermentations was investigated. Initially, ethanol production was monitored in fermentation medium containing 50 g/L glucose plus 45 g/L cellobiose. Inoculum levels and times of inoculum addition were varied. Of the conditions tested, the most rapid rates of ethanol formation occurred in fermentations in which either C. wickerhamii and S. cerevisiae were coinoculated at a ratio of 57 : 1 cell/mL or in fermentations in which a 10‐fold‐greater S. cerevisiae inoculum was added to a pure culture C. wickerhamii fermentation after 1 day incubation. These conditions were used to attempt to enhance fermentations in which cellodextrins produced by trifluoroacetic acid hydrolysis of cellulose served as the sole carbon source. Cellodextrins that were not further purified after cellulose hydrolysis contained compounds that were slightly inhibitory to C. wickerhamii. In this case the mixed‐culture fermentations produced 12–45% more ethanol than a pure culture C. wickerhamii fermentation. However, if the substrate was treated with Darco G‐60 charcoal, the toxic materials were apparently removed and the pure culture C. wickerhamii fermentations performed as well as the mixed‐culture fermentations.
Gas holdup in an external‐loop air‐lift fermentor with a contaminated gas distributor
Authors: McManamey W. J. , Wase D. A. J. , Raymahasay S.
Published: December 2004

Contamination of the porous‐plate gas distributor was observed in an air‐lift fermentor used for Aspergillus fumigatus fermentations. Comparisons between gas holdups measured with uncontaminated distributors and the contaminated one showed that the contamination had no effect on gas holdups in water but reduced the holdups in sodium chloride and sodium sulfate solutions, probably due to increased bubble coalescence. A correlation for gas holdups with clean distributors2 could be used to represent the results for the comtaminated distributor by changing the values used for the characteristic velocities of the electrolyte solutions.
Entrapment of concanavalin A‐glycoenzyme complexes in calcium alginate gels
Authors: Husain Qayyum , Iqbal Jawaid , Saleemuddin M.
Published: December 2004

Glucose oxidase, invertase, and amyloglucosidase were entrapped in calcium alginate gels as concanavalin A complexes in order to prevent the leaching out of the enzymes from the porous matrix. The free as well as the gel‐entrapped concanavalin A‐glycoenzyme complexes exhibited a relatively high effectiveness factor, η, indicating good accessibility to the substrates. Concanavalin A‐invertase complex exhibited marked broadening of pH‐activity and temperature‐activity profiles and was highly resistant to temperature inactivation even after entrapment in the alginate beads. It was possible to entrap considerable quantities of invertase as concanavalin A complex in the beads without a marked decrease in η. A column containing crosslinked concanavalin A‐invertase complex entrapped in alginate beads retained the ability to completely hydrolyze 1M sucrose even after continuous operation for over four months.
Aspartate glucan, glycine glucan, and serine glucan for the removal of cobalt and copper from solutions and brines
Authors: Muzzarelli Riccardo A. A. , Tanfani Fabio , Emanuelli Monica , Bolognini Luigi
Published: December 2004

Aspartate glucan, glycine glucan, and serine glucan obtained by reductive amination of oxalacetic acid, glyoxylic acid, and β‐hydroxypyruvic acid, respectively, with polyglucosamine were tested as chromatographic chelating media. Crosslinked glycine glucan exhibited high capacities for cobalt and copper, even in acidic solutions (pH 2.9). Breakthrough points for 10 mg/L solutions through 6.0 × 0.6 cm columns containing 200 mg of polymer were at 1.8 L for both ions; for 1 mg/L solutions, they were at 4.0 and 12.0 L for cobalt and copper, respectively. Crosslinked glycine glucan could remove microgram amounts of cobalt and copper from fluoride and chloride brines. Cobalt and copper could be separated by elution with 0.25M sulfuric acid.
Solid‐state fermentation of sweet sorghum to ethanol in a rotary‐drum fermentor
Authors: Kargi Fikret , Curme James A.
Published: December 2004

Sugar compounds present in chopped solid‐sweet sorghum particles were fermented to ethanol in a rotarydrum fermentor (RDF) using an ethanol tolerant yeast strain. The influence of rotational speed of the RDF on the rate of ethanol fermentation was investigated and compared with static flask experiments. The rate of ethanol formation decreased with increasing rotational speed. The maximum rate and extent of ethanol formation were ca. 3.1 g EtOH/L h (based on expressed juice volume) and ca. 9.6 g EtOH/100 g mash, respectively, at 1 rpm rotational speed.
Recycle hollow fiber enzyme reactor with flow swing
Authors: Park Tai Hyun , Kim In Ho , Chang Ho Nam
Published: December 2004

The hollow fiber enzyme reactor with pulsation developed by Kim and Chang (1983) was operated in a differential mode by recycling a substrate solution, in order to assess the efficiency of ultrafiltration swing. The rates of lactose conversion by β‐galactosidase contained in the shell side of the reactor were measured to determine the effects of recirculation rate, pulsation period, and amplitude. The conversion increased with the increase of recirculation flow rate and the amplitude while variation in period affected the conversion relatively little. The maximum increase of 113% in the activity was observed in the reactor with pulsation as compared to that without pulsation. The two‐compartment model well described the experimental data obtained in this study. Square‐wave pulsation was theoretically more effective in increasing conversion than sine wave pulsation. However, in experimental operation the damping effect of the hollow fiber wall narrowed the difference between these two wave forms.
Steady‐state and transient behavior in microbial methanification: II. Mathematical modeling and verification
Authors: Bhatia D. , Vieth W. R. , Venkatasubramanian K.
Published: December 2004

It has been shown that the Upflow Anaerobic Sludge Bed (UASB) system data reported earlier1 cannot be explained by simple Monod‐type substrate consumption patterns. An autoinhibition model was also ruled out because the substrate concentration range over which hysteresis was observed was much larger than such a model would predict. However, propionic and acetic acids were found to inhibit each other's conversion machineries. Since in the UASB system the biocatalyst is flocculated, it was found that a model additionally incorporating this facet of the reactor set‐up could explain the steady‐state data very well. Using the parameters generated from steady‐state data and data from butyric acid step change,1 i.e., the entire set of parameters (Table I), a very good agreement between predicted and observed data was found. International Mathematical and Statistical Libraries (IMSL) and Upjohn's NONLIN library combined with various root‐finding and integrating subroutines were used for parameter estimation. The model thus described was used to predict the response of the UASB system when acetic acid and propionic acid influent concentrations were stepped‐up/down. The agreement between the predicted and observed data was found to be excellent in each case during the step‐up schedule. During the step‐down the data seemed to indicate that the UASB system, like any other chemostat, responded faster than predicted. This could be due to the fact that when the culture has to “gear up” part of the lag time is the time required for the cell to produce the requisite amount of enzymes. In the case of “gearing down” this time is not required and the system responds faster.
Experimental adaptive on‐line optimization of cellular productivity of a continuous bakers' yeast culture
Authors: Rolf Michael J. , Lim Henry C.
Published: December 2004

An adaptive on‐line optimization method that utilizes dynamic model identification has been applied to maximize the cellular productivity of a continuous bakers' yeast culture. Experiments were conducted on a sophisticated computerized fermentation system. Experimental results show that the adaptive on‐line optimization method requires very little a priori information, is easy to implement, converges quickly, adapts to changes in the process, and is stable even when operational difficulties are encountered.
Optimization of organic solvent in multiphase biocatalysis
Authors: Brink L. E. S. , Tramper J.
Published: December 2004

The microbial epoxidation of propene and 1‐butene was used to study some fundamental aspects of two‐liquid‐phase biocatalytic conversions. Introduction of a water‐immiscible organic solvent phase in a free‐cell suspension gave rise to a series of undesired phenomena, e.g., inactivation by the solvent, clotting of biomass, and aggregation of cells at the liquid‐liquid interface. Immobilization of the cells in hydrophilic gels, e.g., calcium alginate, prevented direct cell‐organic solvent contact and the related clotting and aggregation of biomass. However, the gel entrapment did not seem to provide additional protection against the organic solvent. The influence of various organic solvents on the retention of immobilized‐cell activity was related to solvent properties like the polarity (as expressed by the Hildebrand solubility parameter) and the molecular size (as expressed by the molecular weight or molar volume). High activity retention was favored by a low polarity in combination with a high molecular weight. The solubility parameter also proved useful to describe the capacity of various organic solvents for oxygen and alkene oxides. This facilitated the optimization of the solvent polarity.
An ultrafiltration membrane reactor for obtaining experimental reaction rates at defined concentrations of inhibiting sugars during enzymatic saccharification of alkali‐pretreated sallow: Formulation of a simple empirical rate equation
Authors: Frennesson Ingrid , Trägårdh Gun , Hahn‐Hägerdal Bärbel
Published: December 2004

The kinetics of the enzymatic hydrolysis of sodium hydroxide‐pretreated sallow were studied in an ultrafiltration membrane reactor in the presence of different concentrations of glucose. In the UF membrane reactor low‐molecular‐weight products were continuously removed at a low dilution rate and replaced by a buffer solution that contained different concentrations of glucose, which made it possible to keep the inhibiting product concentration constant throughout an experiment. The reaction rate was related to the degree of substrate conversion and a mathematical relationship was formulated that describes the influence of the product concentration on the rate coefficient.
A Mathematical model for ethanol production by extractive fermentation in a continuous stirred tank fermentor
Authors: Kollerup Finn , Daugulis Andrew J.
Published: December 2004

Extractive fermentation is a technique that can be used to reduce the effect of end product inhibition through the use of a water‐immiscible phase that removes fermentation products in situ. This has the beneficial effect of not only removing inhibitory products as they are formed (thus keeping reaction rates high) but also has the potential for reducing product recovery costs. We have chosen to examine the ethanol fermentation as a model system for end product inhibition and extractive fermentation and have developed a computer model predicting the productivity enhancement possible with this technique together with other key parameters such as extraction efficiency and residual glucose concentration. The model accommodates variable liquid flowrates entering and leaving the system, since it was found that the aqueous outlet flowrate could be up to 35% lower than the inlet flowrate during extractive fermentation of concentrated glucose feeds due to the continuous removal of ethanol from the fermentation broth by solvent extraction. The model predicts a total ethanol productivity of 82.6 g/L h if a glucose feed of 750 g/L is fermented with a solvent having a distribution coefficient of 0.5 at a solvent dilution rate of 5.0 h−1. This is more than 10 times higher than for a conventional chemostat fermentation of a 250 g/L glucose feed. The model has furthermore illustrated the possible trade‐offs that exist between obtaining a high extraction efficiency and a low residual glucose concentration.
Effect of culture phasing and mannanase on production of cellulase and hemicellulase by mixed culture of Trichoderma reesei D 1–6 and Aspergillus wentii pt 2804
Authors: Ghose T. K. , Panda T. , Bisaria V. S.
Published: December 2004

Significant increase in extracellular cellulase and hemicellulase activities was observed in the biosynthesis of cellulase enzyme in mixed culture fermentation of Trichoderma reesei D 1–6 and Aspergillus wentii Pt 2804 when the A. wentii inoculation was phased by 15 h. The optimal conditions of fermentation by the mixed culture have been established. Presence of mannanase has been found to affect the release as well as activity of cellulase enzyme produced in mixed culture.
A Study of the cellulases produced by three mesophilic actinomycetes grown on bagasse as substrate
Authors: Van Zyl Willem H.
Published: December 2004

The cellulases that strains of Streptomyces albogriseolus, S. nitrosporeus, and Micromonospora melanosporea produce when grown on untreated ballmilled bagasse were investigated. Optimum conditions for extracellular cellulase production and activity were determined to be growth at pH 6.7−7.4 and 25–35°C for 4–5 days and assay at pH 5.0−6.0 and 45–55°C, respectively. The endoglucanases were thermally stable at 50°C, but the Avicelases had a half‐life of approximately 24 h at this temperature. Nearly half of the endoglucanases and almost all of the Avicelases were absorbed on ballmilled bagasse after 15 min incubation at 50°C. The β‐glucosidases were found to be mainly intracellular or cell wall bound. These mesophilic actinomycetes concomitantly produced xylanases and β‐xylosidases with cellulases that, apart from cellobiose and glucose, also release xylose from bagasse. This feature may be advantageous in the commerical application of the enzymes of mesophilic actinomycetes for the saccharification of natural cellulosic substrates.
Performance evaluation of an anoxic/oxic activated sludge system: Effects of mean cell residence time and anoxic hydraulic retention time
Authors: Shieh Wen K. , Chen Chiu Y.
Published: December 2004

A laboratory investigation has been undertaken to asses the effects of two operating parameters, mean cell residence time (MCRT) and anoxic hydraulic retention time (HRT), on the performance of an anoxic/oxic activated sludge system. The performance of the system was evaluated in terms of its COD, nitrogen, and biomass characteristics. An activated sludge system is capable of producing a better effluent, in terms of COD and nitrogen characteristics, when it is operated in an anoxic/oxic fashion. A longer MCRT and an adequate anoxic HRT are desirable in the operation of an anoxic/oxic activated sludge system. For the wastewater used in this investigation, the anoxic/oxic unit was capable of producing an effluent with the following characteristics when it was operated at MCRT = 20 days, total system HRT = 10 h, and anoxic HRT = 3–5 h: COD = 15 mg/L; VSS = 10 mg/L; TKN = 1.30 mg/L; NH3− N = 0.60 mg/L; and NO2+ NO3− N = 5.0 mg/L. A uniform distribution of biomass is achievable in an anoxic/oxic activated sludge system because of the intensive recirculation/convection maintained. The provision of an anoxic zone in the aeration tank promotes a rapid adsorption of feed COD into the biomass without an immediate utilization for cell synthesis. This, in turn, results in a high microbial activity and a lower observed biomass yield in the system. A tertiary treatment efficiency is achievable in an anoxic/oxic activated sludge system with only secondary treatment operations and costs. A conventional activated sludge system can be easily upgraded by converting to the anoxic/oxic operation with minor process modifications.
Effects of immobilization on growth, fermentation properties, and macromolecular composition of Saccharomyces cerevisiae attached to gelatin
Authors: Doran Pauline M. , Bailey James E.
Published: December 2004

The kinetic properties of Saccharomyces cerevisiae immobilized on crosslinked gelatin were found to be substantially different from those of the suspended yeast. Batch fermentation experiments conducted in a gradientless reaction system allowed comparison of immobilized cell and suspended cell performance. The specific rate of ethanol production by the immobilized cell was 40–50% greater than for the suspended yeast. The immobilized cells consumed glucose twice as fast as the suspended cells, but their specific growth rate was reduced by 45%. Yields of biomass from the immobilized cell population were lower at one‐third the value for the suspended cells. Cellular composition was also affected by immobilization. Measurements of intracellular polysaccharide levels showed that the immobilized yeast stored larger quantities of reserve carbohydrates and contained more structural polysaccharide than did suspended cells. Flow cytometry was used to obtain. DNA, RNA, and protein frequency functions for immobilized and suspended cell populations. These data showed that the immobilized cells have higher ploidy than cells in suspension. The observed changes in immobilized cell metabolism and composition may have arisen from disturbance to the yeast cell cycle by the cell attachment, causing alterations in the normal pattern of yeast bud development, DNA replication, and synthesis of cell wall components.
Biomass yields and energetic yields of oleaginous yeasts in batch culture
Authors: Pan Jae G. , Rhee Joon S.
Published: December 2004

This article provides the analysis on biomass yields and energetic yields of the oleaginous yeasts. The biomass yields of the oleaginous yeasts are consistently lower than nonoleaginous microorganisms, whereas their energetic yields are higher. Data inconsistencies of literature are explained by the variation of energy contents of oleaginous yeasts.
Spore production of Penicillium roqueforti by solid state fermentation: Stoichiometry, growth and sporulation behavior
Authors: Desfarges Chantal , Larroche Christian , Gros Jean‐Bernard
Published: December 2004

The development of Penicillium roqueforti on buckwheat seeds proceeds roughly into four steps, involving a lag phase and three growth phases. First, it appears as a spore germination and external colonization of the grains by the mycelium. Then, mainly external sporulation and internal colonization of the seeds occur and finally internal sporulation takes place. The Stoichiometry of the growth and the sporulation is established. Kinetic experiments performed in a fixed bed reactor show that the growth of the microorganism (biomass production) may be estimated by the protein content of the medium. This growth occurs with a very low μmax value close to 0.030 h−1. The chitin content of the medium is an indicator of the sporulation, just as the metabolic liquor (mainly water) produced during the course of a cultivation. The values of the observed respiratory quotient are close to those predicted by stoichiometry.
Anaerobic saccharolytic bacterial adhesion to raw starch granules
Authors: Wang Hsi‐Hua , Chiou Tsyy‐Wen , Hsu Jyh‐Ping
Published: December 2004

The experiment of bacteria adhesion onto starch granules is conducted. It is found that anaerobic saccharolytic bacteria have the highest adhesion ability in their growth and initial stage of stationary phase. Starch granules with a low crystallinity, low bulk density, and high water‐holding capacity have a high adhesion capacity. The optimum temperature for both bacterial growth and their adhesion is 30°C. The optimum pH for the bacterial adhesion range from 5.0 to 6.5. Anaerobic conditions cause an appreciable decrease in percentage of adhesion. The percentage of adhesion is not sensitive to the type of soluble saccharide on which bacteria were grown.
Air‐stripping effects on cell growth with volatile substrates
Authors: Singh Nona , Hill G. A.
Published: December 2004

The removal of substate molecules from aerobic microbial cultures is due to both consumption by microorganisms and stripping by the air stream. The air stripping component can be described by a constant parameter for low concentrations of volatile substrates. This air stripping parameter was found to have a value of 0.0033 h−1 for phenol molecules in a typical fermentation situation. The determination and inclusion of this constant is important for modeling microbial growth. For Pseudomonas putida growing on phenol, it is shown that air stripping is responsible for all of the original decline in phenol concentration. Further, the kinetic inhibition constant is sensitive to both the value of the air stripping parameter and the value of the initial concentration of bacteria. The experimental data for Pseudomonas putida growing on phenol was fit by a non‐linear, least squares technique to isolate the inhibition constant between 100 and 600 ppm.
Optimal temperature control for batch beer fermentation
Authors: Gee Douglas A. , Ramirez W. Fred
Published: December 2004

Optimal control theory was applied to the process of batch beer fermentation. The performance functional considered was a weighted sum of maximum ethanol production and minimum time. Calculations were based on the model of Engasser et al. modified to include temperature effects. Model parameters were determined from isothermal batch fermentations. The fermentor cooling duty was the single available control. Temperature state variable constraints as well as control variable constraints were considered. The optimal control law is shown to be bang‐bang control with the existence of a singular arc corresponding to isothermal operation at the maximum temperature constraint. An iterative algorithm is presented for computing appropriate switching times using a penalty‐function‐augmented performance functional.
Mathematical model of microporous hollow‐fiber membrane extractive fermentor
Authors: Fournier Ronald L.
Published: December 2004

A mathematical model is presented for a microporous hollow‐fiber membrane extractive fermentor (HFEF). The model is based on the continuous flow of the aqueous nutrient phase and cells through the shell space of the fermentor where the fermentation reaction occurs. The product diffuses from the shell space through the hollow‐fiber membrane where it is continuously removed by solvent flowing concurrently through the fiber lumen. Results for ethanol production show that the HFEF has a volumetric productivity significantly higher than that possible using conventional methods. The model predicts the existence of an optimum volume fraction of hollow fibers in the fermentor that maximizes the total volumetric productivity. This optimum is the result of a classic trade‐off between the volume fraction of the fermentor required for fermentation and that required for efficient removal of the ethanol product to minimize product inhibition.
Transient characteristics of oxygen probes with significant liquid film effects
Authors: Linek V. , Vacek V. , Beneš P. , Sinkule J.
Published: December 2004

Various experimental procedures for the determination of transient characteristics with significant liquid film effects were tested. A comparison between transient characteristics obtained experimentally and those calculated from rational models indicates that all procedures but one give highly inconsistent results. Recalculation of transient characteristics with no liquid film (easily measured in the gas phase) to that with liquid film (occurring in viscous liquids) is recommended as well as the selected experimental procedure which yields consistent results in the situations where the steady‐state probe reading is decreased up to one‐half due to the liquid film.
Alginate as immobilization material. II: Determination of polyphenol contaminants by fluorescence spectroscopy, and evaluation of methods for their removal
Authors: Skjåk‐Bræk Gudmund , Murano Erminio , Paoletti Sergio
Published: December 2004

Alginates, both commercial and laboratory made, are strongly fluorescent due to small amounts of polyphenolic materials. These contaminants can be detected by fluorescence spectroscopy in concentrations lower than 1 ppm. This technique has been used to measure polyphenols in a wide range of alginates and various procedures for preparation of biotechnological‐grade alginates have been evaluated.
Thermophilic semisolid anaerobic digestion of municipal refuses
Authors: Marique Ph. , Gilles A. , Edeline F. , Joassin L.
Published: December 2004

Comparison of both mesophilic (35°C) and thermophilic (55°C) anaerobic digestions of the organic fraction of municipal refuses in pilot digesters designed to process in a semisolid phase at total solids concentrations of ca. 25% shows that the average gas production is 20–25% higher in thermophilic conditions than in mesophilic conditions even for a retention time of 10 days. These results and the data recorded during long periods of experimentation indicate that the process allows to increase the net energy production and to improve the economical balance of an industrial plant.
Studies on growth and cardenolide production of Digitalis lanata tissue cultures
Authors: Tuominen U. , Toivonen L. , Kauppinen V. , Markkanen P. , Björk L.
Published: December 2004

Digitalis lanata cell cultures grown as small undifferentiated aggregates in suspension culture can be redifferentiated into green embryos that produce cardenolides. The possibility of using a statistical (Box–Wilson) experimental design to study the effects of four different variables on growth, differentiation, and cardenolide production of D. lanata tissue cultures are investigated. The results of the analyses were processed by linear regression analysis. Mathematical models explaining the effects of the variables were developed. The concentration of maltose and the NO3−NH4+ ratio were found to be significant variables for both growth and cardenolide production. The size of the inoculum was also important.
Optimization of batch fermentor sterilization
Authors: Singh V. , Hensler W. , Fuchs R.
Published: December 2004

This article presents a calculation procedure useful for the optimization and scale up of batch sterilization cycles in large‐scale fermentors. This technique determines the sterilization temperature and hold‐time necessary to minimize nutrient damage in a specific fermentor. The method can also be used for “scaledown” experiments to eliminate sterilization conditions as a scale up parameter. A method for the systematic evaluation of different sterilization conditions on product yield is also presented. This procedure is useful in determining if scale up of sterilization conditions is important for a given process. The validity of the techniques presented are supported by data showing significant yield improvements in a 1.2 × 105 L antibiotic fermentation.
Hydrodynamics and mass transfer in Aspergillus niger fermentations in bubble column and loop bioreactors
Authors: Allen D. Grant , Robinson Campbell W.
Published: December 2004

The influence of Aspergillus niger broth rheology, bioreactor geometry, and superficial gas velocity on the volumetric liquid phase oxygen transfer coefficient (kLaL), riser gas holdup (εGR), and circulating liquid velocity (uLR) was studied in a bubble column (BC) and two external‐circulation‐loop airlift (ECLAL) bioreactors. The results are compared to those of previous studies on homogeneous fluids and in particular with a recent study on non‐Newtonian carboxymethylcellulose (CMC) solutions conducted in the same contactors used for the A. niger fermentations. As expected from the CMC‐based studies, in the heterogeneous broths of A. niger εGR, kLaL, and uLR decreased with increasing broth apparent viscosity; εGR and kLaL decreased with increasing downcomer‐to‐riser cross‐sectional area ratio, Ad/Ar, whereas uLR increased with increasing Ad/Ar. Gas holdup data in the airlift fermentations of A. niger were well predicted by the CMC‐based correlation. However, the CMC‐based correlations produced conservative estimations of kLaL and overestimates of uLR compared to the observed values in the A. niger broths.
Intramolecular esterification by lipase powder in microaqueous benzene: Effect of moisture content
Authors: Yamane Tsuneo , Kojima Yoshikazu , Ichiryu Takayuki , Nagata Masahiro , Shimizu Shoichi
Published: December 2004

In view of the biochemical reaction catalyzed by enzyme powder suspended in a water‐insoluble organic solvent, an equation was derived to estimate the amount of water bound to the enzyme powder. With this equation, an apparent adsorption isotherm between free water (water freely dissolved in benzene) and bound water (water bound to crude lipase powder of Pseudomonas fluorescens) was obtained. A direct lactonization reaction (synthesis of cyclopentadenolide from 15‐hydroxypen‐tadecanoic acid) catalyzed by crude lipase powder of Pseudomonas fluorescens was carried out batchwise in microaqueous benzene at 40oC. A kinetic model of the enzymatic reversible lactonization reaction was derived, from which the effect of moisture content on the initial reaction rate with a fully hydrated enzyme was mathematically expressed. The observed initial reaction rate first increased, then decreased with increasing moisture content, giving rise to the maximum rate at a certain level of the moisture content. The drop in the reaction rate at lower moisture content was due to a lesser hydration of the enzyme molecule (hydration‐limited) and the decrease in the reaction rate at higher moisture content was attributed to the dependence of the true initial rate of the reversible reaction on the moisture content (true reversible reaction limited), and could be simulated by the kinetic model. The equilibrium yield approached 100% at a lower moisture content.
Calculation of the heat of growth of Escherichia coli K‐12 on succinic acid
Authors: Battley Edwin H.
Published: December 2004

Using data from the literature, a method is adopted for determining the empirical composition and the unit carbon formula for dried Escherichia coli K‐12 cells by summing the quantities of C, H, O, N, P, and S in each of the major classes of macromolecular substances comprising the cellular biomass. With these data and the molar growth yield of cells on succinic acid, equations are written representing the anabolism and catabolism of E. coli K‐12 on this quantity of substrate. The enthalpy change accompanying catabolism can be calculated directly using standard enthalpies of formation because there is no term representing cellular substance. The enthalpy change accompanying anabolism is calculated to be very small or zero using microcalorimetric and other data from which the enthalpy of formation of a unit quantity of living cellular substance can be obtained. This indicates that the net enthalpy change accompanying the growth process (anabolism plus catabolism) is the same as that calculated for catabolism alone, in agreement with the same conclusion by several investigators using direct microcalorimetry. The method described here of determining the unit carbon formula and the quantity of ash remaining after cellular combustion is compared to that conventionally used in which cellular P and S is considered either to be negligible or to be a part of the ash. It is concluded that equations representing anabolism and the growth process can be written more accurately using the presently described method, leading to more accurate thermodynamic calculations.
Effect of continued exposition to ethanol on activity of the ammonium and fructose transport systems in Saccharomyces cerevisiae var. ellipsoideus
Authors: Iglesias R. , Ferreras J. M. , Arias F. J. , Muñoz R. , Girbés T.
Published: December 2004

Ethanol and cycloheximide inhibited the function of the ammonium transport system in growing cultures of Saccharomyces cerevisiae var. ellipsoideus measured as methylamine uptake. The effect was reversible with ethanol and irreversible with the antibiotic. The kinetic data are consistent with a reduction of the number of active carrier molecules located in the plasma membrane. In contrast, neither ethanol nor cycloheximide affected the specific rate of fructose uptake.
Measurement of bacterial random motility and chemotaxis coefficients: I. Stopped‐flow diffusion chamber assay
Authors: Ford Roseanne M. , Phillips Bret R. , Quinn John A. , Lauffenburger Douglas A.
Published: December 2004

Bacterial chemotaxis, the directed movement of a cell population in response to a chemical gradient, plays a critical role in the distribution and dynamic interaction of bacterial populations in nonmixed systems. Therefore, in order to make reliable predictions about the migratory behavior of bacteria within the environment, a quantitative characterization of the chemotactic response in terms of intrinsic cell properties is needed.

The design of the stopped‐flow diffusion chamber (SFDC) provides a well‐characterized chemical gradient and reliable method for measuring bacterial migration behavior. During flow through the chamber, a step change in chemical concentration is imposed on a uniform suspension of bacteria. Once flow is stopped, diffusion causes a transient chemical gradient to develop, and bacteria respond by forming a band of high cell density which travels toward higher concentrations of the attractant. Changes in bacterial spatial distributions observed through light scattering are recorded on photomicrographs during a 10‐min period. Computer‐aided image analysis converts absorbance of the photographic negatives to a digital representation of bacterial density profiles. A mathematical model (part II) is used to quantitatively characterize these observations in terms of intrinsic cell parameters: a chemotactic sensitivity coefficient, μ0, from the aggregate cell density accumulated in the band and a random motility coefficient, μ, from population dispersion in the absence of a chemical gradient.

Using the SFDC assay and an individual‐cell‐based mathematical model, we successfully determined values for both of these population parameters for Escherichia coli K12 responding to fucose. The values obtained were μ = 1.1 ± 0. 4 × 10−5 cm2/s and χo = 8 ± 3 ± 10−5 cm2/s. We have demonstrated a method capable of determining these parameter values from the now validated mathematical model which will be useful for predicting bacterial migration in application systems.
A new procedure for enzymatic semisynthesis of human insulin by hydrolysis of single‐chain des‐(b‐30)‐lnsulin precursor with lysyl endopeptidase
Authors: Morihara Kazuyuki , Ueno Yoshihiko
Published: December 2004

It has been shown that the single‐chain des‐(B‐30)‐insulin precursor (SCI) can be converted into human insulin ester by transpeptidation using trypsin in the presence of a threonine derivative. The present study demonstrates that Achromobacter lyticus protease 1 (lysyl endopeptidase) can catalyze the transpeptidation reaction more efficiently than can trypsin. It is also shown that des‐(B‐30)‐insulin (DAI) can be produced by hydrolysis of SCI with the lysyl endopeptidase. Since it is well known that SCI can be produced by gene technology, the following method is recommended for industrial production of human insulin ester: hydrolysis of SCI with lysyl endopeptidase followed by coupling of the resulting DAI with a threonine derivative using trypsin or lysyl endopeptidase.
Prediction of effects of amino acid supplementation on growth of E. coli B/r
Authors: Shu J. , Shuler M. L.
Published: December 2004

A mathematical model for the growth of a single cell of E. coli on medium containing amino acid is presented. A mixture of purified amino acids (glutamate, aspartate, serine, tyrosine, and leucine) combined in the ratios found in a natural digest (casein) were employed as the nitrogen source. Each of these amino acids is the representative of a different family of amino acids. The transport mechanisms and assimilation routes for each amino acid were inserted into the prototype model. The enzyme activities and saturation constants used in the model were based on literature data. The maximum velocities for uptake systems were calculated from experimental data. The formation and homeostasis of amino acid pools were regulated through cross‐control of the activities of biosynthetic enzymes and of membrane transport of exogenous nutrients. The size of each amino acid pool was determined with mass balance equations that included terms for a transport system, a biosynthesis system, a transaminase enzyme system for interchange between the amino acid families, and a consumption system. The predictions of the extended model with regard to nutrient concentrations and growth rates compared well with the experimental data.
Translation of immobilized genetic information by yeast cell‐free protein synthesizing system
Authors: Kobatake Eiry , Ikariyama Yoshihito , Aizawa Masuo
Published: December 2004

A cell‐free protein‐synthesizing system for the purpose of specific genetic information translation was constructed: ribosome, t‐RNA, and enzymes extracted from yeast cells were combined with an immobilized mRNA. The soluble fraction mixed with energy sources and amino acids was incubated with the immobilized mRNA such as poly(U), yeast mRNA, and myeloma mRNA to incorporate [3H]phenylalanine into polypeptides of de novo synthesis. By supplying amino acids to these protein‐synthesizing systems, amino acid incorporation was ascertained. Lower efficiency of the incorporation in the immobilized system than that of the homogeneous system was mainly attributed to the heterogeneous reaction where the mass‐transfer process is diffusion limited. Results obtained show the possibility of a system for specific translation of a desired genetic code.
Reaction characteristics and stability of a membrane‐bound enzyme reconstituted in bilayers of liposomes
Authors: Kheirolomoom Azadeh , Katoh Shigeo , Sada Eizo , Yoshida Ken‐Ichi
Published: December 2004

The effects ensuing from the interaction between membrane‐bound sarcosine dehydrogenase and the surrounding lipids as well as the effects of membrane fluidity were described in this study. A 25‐fold activation was observed upon the reconstitution of the enzyme in bilayers of SUVs made of DMPC. The considerable decrease in Km and increase in Vmax suggest the induction of favorable conformational changes in both the substrate‐binding site and the catalytic site of the enzyme due to the lipid–protein interaction. In SUVs of negatively charged phospholipids, the enzyme retained its initial activity over 1 month. The break point in the Arrhenius plot of the activity of reconstituted enzyme was found at temperatures close to the gel–liquid crystalline transition point of the phospholipid showing that the activity is sensitive to the physical state of membrane phospholipids. Further, immobilization of the reconstituted enzyme by use of ENT prepolymer resulted in a high activity, whereas no remarkable activity was detected with the immobilized enzyme without reconstitution.
Optimal nonsingular control of fed‐batch fermentation
Authors: Kurtanjek Ž.
Published: December 2004

Presented is a new simple method for multidimensional optimization of fed‐batch fermentations based on the use of the orthogonal collocation technique. Considered is the problem of determination of optimal programs for fermentor temperature, substrate concentration in feed, feeding profile, and process duration. By reformulation of the state and control variables is obtained a nonsingular form of the optimization problem which has considerable advantage over the singular case since a complicated procedure for determination of switching times for feeding is avoided. The approximation of the state variables by Lagrange polynomials enables simple incorporation of split boundary conditions in the approximation, and the use of orthogonal collocations provides stability for integration of state and costate variables. The interpolation points are selected to obtain highest accuracy for approximation of the objective functional by the Radau–Lobatto formula. The control variables are determined by optimization of the Hamiltonian at the collocation points with the DFP method. Constraints are imposed on state and control variables.

The method is applied for a homogeneous model of fermentation with volume, substrate, biomass, and product concentrations as the state variables. Computer study shows considerable simplicity of the method, its high accuracy for low order of approximation, and efficient convergence.
Absorption of CO2 in algal mass culture systems: A different characterization approach
Authors: Talbot P. , Gortares M. P. , Lencki R. W. , de la Noüe J.
Published: December 2004

For the characterization of CO2 absorption in aerated microalgal culture systems, a different approach based on KLa(O2) determination and transformation was studied. To confirm the validity of this method, the influence of reactions between CO2 and compounds (OH−, H2O, and NH3) present in the culture medium upon the absorption mechanism was evaluated under different physical and chemical culture conditions. Under these conditions, knowledge of the relative magnitudes of the diffusion and reaction kinetics permitted the evaluation of their relative importance. For the determination of the parameters required for the calculation of the CO2 absorption constant, empirical correlations for K and a were used that had been previously verified with experimental data for O2 absorption. Since, for the conditions studied, the absorption rate was shown to be independent of the chemical reactions taking place in the liquid phase, the KLa for CO2 could be directly related to the KLa for O2 by a simple factor that took into account the difference in aqueous diffusivity of the two gases. Thus, using methods developed for determining O2 absorption in gas–liquid contactors, it is possible to adequately characterize CO2 absorption for laboratory and pilot scale algal production systems.
Characterization of the biochemical behavior of glucose oxidase entrapped in a polypyrrole film
Authors: Fortier Guy , Bélanger Daniel
Published: December 2004

This article reports the characterization of the biochemical behavior of glucose oxidase entrapped in polypyrrole. The immobilization of glucose oxidase in a polypyrrole film was performed by entrapment during the electropolymerization of pyrrole at a platinum electrode poised at 0.65 V vs. SCE in aqueous solution in a one‐compartment electrochemical cell. Thin films of polypyrrole (0.11 μm) were obtained and the entrapped enzyme obeyed Michaelis kinetics, indicating no diffusional constraints of the substrate. Our results indicate that the entrapped glucose oxidase is more resistant to denaturation conditions such as alkaline pH and temperature (50 and 60°C) than the soluble form of the enzyme. The autoinactivation constant for the entrapped enzyme was also determined in presence of 0.25M of glucose and was 6.19 × 10−4 min−1, i.e., corresponding to a half‐life value of 20 h. The results reported here show clearly that polypyrrole matrix has a strong stabilizing effect on the stucture and on the activity of glucose oxidase.
Influence of pH, temperature, and inoculum composition on mixed cultures of Streptococcus thermophilus 404 and Lactobacillus bulgaricus 398
Authors: Beal C. , Corrieu G.
Published: December 2004

The effects of pH, temperature, and inoculum composition on Streptococcus thermophilus 404 and Lactobacillus bulgaricus 398 mixed cultures were studied. Linear quadratic models according to these three variables were proposed to express the growth and acidification characteristics, as well as the final proportion between the two strains. Initial and operating conditions, allowing maximization of these characteristics were determined. Finally, a graphic method to predict both final total concentration and final proportion of the two bacteria as a function of pH, temperature and inoculum composition is presented.
Influence of the screen material on the fouling of spin filters
Authors: Esclade Laurent R. J. , Carrel Stéphane , Péringer Paul
Published: December 2004

Mouse–mouse hybridomas (15 μm mean diameter) were cultivated in a simulated perfusion reactor with spin filter and external recirculation of the medium. Proteins at high concentrations, such as 10% foetal calf serum (FCS), were found to be not responsible by themselves for fouling, even at high recirculation rates. Stainless steel (10 μm pores) in contrast to polyamide (11 μm proes) led to a great accumulation of dead cells and nucleic acids on the screen, finally leading to fouling, as shown by biochemical and microscopic examinations. It is suggested that the high surface charge density of metals compared to polyamide is responsible for attachment of various residues. Stainless steel should rather be replaced by a resistant and nontoxic synthetic material, such as polyamide 66 which was successfully used. FCS should be avoided, since it seems to increased the fouling phenomenon. Moreover, the pore size of the screen should be carefully defined according to the wide size distribution of living and dead cells of the line used (33% of variation of the mean size in our case) as well as fragments. The purpose of the screen being to get rid of fragments and small dead cells, and not to wash too many new small cells, a good retention was achieved here by a 10‐μm opening.
Measurement and regulation of the culture reduction state in Clostridium acetobutylicum
Authors: Srivastava A. K. , Volesky B.
Published: December 2004

With a constant glucose feed concentration, the change in the continuous culture dillution rate resulted in an altered fermentation profile and the cellular NADH content. The cultures growing at high dillution rates demonstrated an oxidative metabolism low NADH and butanol concentrations. The low specific NADH flourescence (F/X) at high butanol production rates suggested that a rapid regeneration of NADH to NAD is essential for a high solventogenic culture activity. The culture florescence and butanol concentration remained constant in the solventogenic dilution rate range of D = 0.05–0.2 h−1 with an inverse relationship between the specific flourescence (F/X) and the specific butanol production rate, qB. Flourometric NADH observations were confirmed by enzymatic NADH determination. The stiochiometric “Fermentation Equation” was used to check the experimental data consistency and to investigate the role of the available biosynthetic and reduction energy on the culture metabolic activities under different growth conditions. The butanol concentration in the broth was stabilized in a fed‐batch process when the culture NADH fluorescence was being controlled through the addition of fresh medium.