bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrocarbon recovery and biocompatibility of solvents for extraction from cultures of Botryococcus braunii
Authors: Frenz J. , Largeau C. , Casadevall E. , Kollerup F. , Daugulis A. J. 
Published: December 2004

AbstractVarious water‐immiscible solvents were tested for biocompatibility and hydrocarbon recovery under different contact conditions with the hydrocarbon‐rich microalga Botryococcus braunii. Eighteen solvents were first selected from a database of 1500 compounds (compiled for solvent selection for ethanol recovery from Saccharomyces cerevisiae fermentation). Nine of these candidate solvents were shown to be biocompatible with B. braunii following short contact times. This biocompatibility tends to be associated with high molecular weights and high boiling points but strongly depends on solvent chemical structure. A low polarity is essential to biocompatibility and calculated octanol–water partition coefficients, or capacity factors determined by reversed‐phase high‐performance liquid chromatography (HPLC), are suitable predictors of biocompatibility with B. braunii. High recoveries of hydrocarbons directly from the algal culture require relatively polar solvents and are, therefore, inimical with maintenance of cell viability. The inaccessibility of weakly polar solvents to the cell surface appears to protect the algae but also prevents substantial recovery of the hydrocarbons stored in B. braunii outer walls. In order to achieve a high recovery, contact with the solvent must be carried out on algae concentrated by filtration. Then, a large fraction of B. braunii hydrocarbons can be recovered, after a short contact time, without impairing cell viability. Under these conditions, the pertinent solvent property is affinity for the nonpolar hydrocarbons, and the highest recovery yield, ∼70% after contact for 30 min, is achieved with hexane.
A new graphical method for determining parameters in Michaelis–Menten‐type kinetics for enzymatic lactose hydrolysis
Authors: Yang Shang‐Tian , Okos Martin R. 
Published: December 2004

AbstractA new graphical method was developed to determine the kinetic parameters in the Michaelis–Menten‐type equation. This method was then applied to studying the kinetics of lactose hydrolysis by Aspergillus niger β‐galactosidase. In this study, the reaction temperature ranged between 8 and 60°C, and the initial lactose concentration ranged between 2.5 and 20%. A kinetic model similar to the conventional Michaelis–Menten equation with competitive product inhibition by galactose was tested using this graphical method as well as a nonlinear computer regression method. The experimental data and the model fit together fairly well at 50°C. However, a relative large disparity was found for reactions at 30°C. A three‐parameter integrated model derived from the reversible reaction mechanism simulates the experimental data very well at all temperatures studied. However, this reversible reaction model does not follow the Arrhenius temperature dependence. Nevertheless, reaction rate constants for the proposed model involving the enzyme‐galactose complex (in addition to the Michaelis complex) as an intermediate in lactose hydrolysis follow the Arrhenius temperature dependence fairly well, suggesting that this model can be best used for describing the enzymatic lactose hydrolysis. The lack of fit between the model predictions and data may be largely attributed to the effects of galactose mutarotation and oligosaccharide formation during lactose hydrolysis.
Measurement of enzyme reaction rates using advanced pH control system: Application of repetitive PF system
Authors: Shimizu Hiroshi , Sada Eizo , Shioya Suteaki , Suga Ken‐ichi 
Published: December 2004

AbstractThe aim of this article is to develop the on‐line measurement system of enzyme reaction rates, using an advanced pH controller, which is called a repetitive PF(Programmed Controller/Feedback Compensator) System. In the esterolysis reaction of the N‐acetyltyrosine ethyl ester by α‐chymotrypsin, the enzyme reaction rate could be calculated from the amount of base required for keeping the pH constant. The proposed controller has a learning mechanism in which the knowledge is obtained from the former results of the repetition, and pH was controlled much more successfully by the proposed repetitive PF System than by the conventional on‐off controller, PI controller, and the adaptive controller. The enzyme reaction rate could be evaluated each time as accurately as possible based on the result of the controlled batch reaction. Using Lineweaver–Burk plots of the estimated reaction rates, kinetic parameters, such as the enzyme activity and Michaelis–Menten constant, could be estimated more accurately and from fewer experiments by the repetitive PF system than by initial reaction rates using on‐off pH‐stat.
pH‐Dependent enzyme deactivation models
Authors: Chitnis Ashish , Sadana Ajit 
Published: December 2004

AbstractA pH‐dependent “series‐type” enzyme deactivation model using rapid protonation and deprotonation equilibria and the relatively slower inactivation rates is presented. From the enzyme activity‐time trajectories at different pH the models presented permit the evaluation of some of the protonation and inactivation rate constants as well as the specific activities of the different enzyme forms. pH dependence of enzyme deactivations may also exhibit deactivation disguised kinetics. Three different examples of pH‐dependent enzyme deactivations available in the literature are appropriately modeled to indicate the general applicability of the model. The model presented is consistent with the data and provides mechanistic insights into the pH‐dependent deactivation of different enzymes.
Analysis of the biomass quality and photosynthetic efficiency of a nitrogen‐fixing cyanobacterium grown outdoors with two agitation systems
Authors: Fontes Agustin G. , Moreno José , Vargas M. Angeles 
Published: December 2004

AbstractThe efficiency of two different agitation systems (airlift and paddlewheel) in the biomass photoproduction of a nitrogen‐fixing filamentous blue‐green alga was evaluated outdoors, and the elemental and molecular composition of the cells grown with each system was analyzed. With the paddlewheel system, the productivity values achieved were over 30% higher than with the airlift system, both in summer and winter. In this last season, a conversion efficiency of total solar energy into stored biomass energy of 3.3% was estimated for the paddlewheel system. Moreover, the algal cells grown with this system exhibited a higher net protein (58.9% of dry weight) and nitrogen (11.3%) content than those grown with the airlift device, with an estimated nitrogen fixation rate of more than 2 g N m−2 day−1. These advantages of the paddlewheel system make this procedure more appropriate for the large‐scale photoproduction of nitrogen‐fixing blue‐green algae outdoors.
Co‐immobilization by adhesion of β‐galactosidase in nonviable cells of Kluyveromyces lactis with Klebsiella oxytoca: Conversion of lactose into 2, 3‐butanediol
Authors: Champluvier B. , Francart B. , Rouxhet P. G. 
Published: December 2004

AbstractKlebsiella oxytoca (NRRL‐B199), although able to produce 2, 3‐butanediol from glucose, converted lactose mainly into acetic acid. By addition of a preparation of lactase (β‐galactosidase, EC 3.2.1.23), the fermentation of lactose in a stirred vessel was three‐times faster and resulted in a high concentration of 2, 3‐butanediol. The lactase confined in dead cells of Kluyveromyces lactis (CBS 683) was prepared by permeabilization with solvents and fixation with glutaraldehyde. The cells were coimmobilized by adhesion to glass wool after treatment of the latter with chitosan, which ensured cell‐support electrostatic attraction. The cell loading (dry weight) was ca. 9 gL−1 for the yeast and ca. 2 gL−1 for the bacteria. In the presence of culture medium, the adhesion of both cells was stable and the bacteria tended to form biofilms. The stability of the coimmobilized cells was demonstrated by the continous conversion of lactose into 2, 3‐butanediol at 30oC during 25 days. The coimmobilization system gave output concentrations (14 gL−1) and rate of production (1 gL−1 h−1) of 2, 3‐butanediol from lactose, similar to those obtained in the literature with immobilized cells and glucose. Compared to the literature data on direct conversion of lactose using pure cultures, the present results showed higher butanediol concentrations and 10 to 100 times higher rates of production.
Two‐stage fermentation with bacteriophage λ as an expression vector in Escherachia coli
Authors: Park Tai Hyun , Seo Jin‐Ho , Lim Henry C. 
Published: December 2004

AbstractThe potential of bacteriophage λ as an expression vector for a large scale production of cloned‐gene proteins was evaluated in batch and continuous bioreactors using a temperature‐sensitive mutant in the cl gene, which allows a simple manipulation of temperature as a means to control the phage in the lysogenic or lytic state. A temperature switch from 32°C (or below) to 38°C (or above) forces the phage to go from the lysogenic state to the lytic state. Temperature cycling and a two‐reactor system were used for continuous cultures. For the latter the first reactor is maintained in the lysogenic state at a lower temperature to stably maintain the foreign DNA in the host cell, while the second reactor is maintained in the lytic state to force replication of the cloned‐gene and overproduction of its products. The results are promising but suggest a greater potential for a mutant which lacks the Q gene which is responsible for host cell lysis and packaging of phage particles.
Adaptive control of dissolved oxygen concentration in a bioreactor
Authors: Lee Seung Chul , Hwang Young Bo , Chang Ho Nam , Chang Yong Keun 
Published: December 2004

AbstractA new adaptive DO (dissolved oxygen) concentration control algorithm considering DO electrode dynamics with response time delay has been developed. A system model with two time‐varying parameters was used to relate the DO concentration with two control variables: air flow rate and agitation speed. Parameters of this model were estimated on‐line using a regularized constant trace recursive least‐squares method. An extended Kalman filter was used to remove the effect of noises from the DO concentration measurements and thus to improve control performance. A discrete one‐step ahead control scheme was adopted to determine control actions based on the parameter estimation results. Experimental results showed that the new adaptive DO concentration control algorithm performed better than other algorithms tested, a PID controller and adaptive algorithms without the DO electrode dynamics.
The effect of pore‐size distribution on the binding of proteins to porous resin beads
Authors: Hasegawa Masanori , Kitano Hiromi 
Published: December 2004

AbstractThe effect of the distribution of pore radii in the resin beads on protein binding was taken into account to analyze the elution profiles of proteins from the polymer‐packed column obtained by repetitive injection method. By assuming that the distribution of pore radii in the resin beads is logarithmic Gaussian, the theoretical curves obtained agreed well with the experimental data.
A three‐dimensional solubility parameter approach to nonaqueous enzymology
Authors: Schneider Luko V. 
Published: December 2004

AbstractWidespread commercial application of enzymes as catalysts for specialty or commodity chemical synthesis will require their use in nonaqueous systems. While a number of non‐aqueous enzyme applications have been demonstrated, the lack of useful rules for predicting enzyme–solvent interactions has hindered the development of this technology. Both Hildebrand and solvent hydrophobicity (octanol–water partition coefficient) parameters have been used previously to correlate and predict enzyme activity in nonaqueous systems, with some success, but any single‐parameter approach is inherently limited in its ability to reflect the spectrum of possible enzyme‐solvent interactions. Therefore, this study evaluates the three‐dimensional solubility parameter space, as proposed by Hansen, to correlate and predict enzyme activity in microaqueous, miscible, and biphasic nonaqueous systems. Preliminary results suggest that Hansen parameters may be useful for correlating nonaqueous enzyme activity, and that the dispersive and polar parameters may be disproportionately important in single‐phase microaqueous systems. The Hansen hydrogen‐bonding parameter appears to be the only parameter yet evaluated capable of correlating the water requirement for enzyme activity in microaqueous systems, suggesting that water affects protein structure through enthalpic rather than entropic processes in nonaqueous systems. Insufficient data are available for miscible and biphasic systems, but it is proposed that enzyme activity may correlate with the average solubility parameters of miscible systems and of the aqueous phase in biphasic systems.
On the estimation of average shear rate in bubble columns
Authors: Nishikawa Masabumi 
Published: December 2004

AbstractDevelopment of bioengineering using such biomaterials as plant tissues or genetically produced microorganisms makes it important to accurately estimate the prevailing shear rate in bioreactors because they are generally sensitive to shear. Various authors have discussed ways to estimate the average shear rate in a bubble column or an airlift reactor.1 This communication will explain the background consideration for the development of the expression as γav = 50 ug by the present authors, and give suggestions for further discussions.
Flocculation of cell debris from ultrasonicated Escherichia coli
Authors: Gellan Elaine , Martin G. F. , Cumming R. H. 
Published: December 2004

AbstractCell debris of Escherichia coli produced by ultrasonication was flocculated with acid. The debris settled at pH 3 and 4, but not at pH 2. Extensive protein precipitate formed in lysates at low pH. The results were compared with whole cells flocculated by acid.
Observations of binary population biofilms
Authors: Siebel Maarten A. , Characklis William G. 
Published: December 2004

AbstractBiofilm research has focused on studies of undefined mixed microbial populations and, more recently, on investigations of monopopulation biofilms. In the first case, the biofilm is considered a homogeneous mass, ignoring the properties of individual species. The second case concentrates on the properties and processes of one microbial species in the biofilm. This article describes biofilm experiments conducted with monopopulations of Klebsiella pneumoniae and Pseudomonas aeruginosa and with binary populations of K. pneumoniae and P. aeruginosa. Process rates and stoichiometric coefficients were determined for the monopopulation and for the binary population biofilms and evaluated in light of the species distribution in the latter. Results indicate that neither the specific cellular product formation rate nor the glucose–oxygen stoichiometric ratio of K. pneumoniae or P. aeruginosa in the binary biofilm is affected by the presence of the other species. Consequently, species interaction was not observed. Although the specific cellular growth rate of K. pneumoniae is five times that of P. aeruginosa, the former species did not dominate the microbial population in the biofilm. Possible reasons for this unexpected behavior are discussed.
A production of monoclonal antibodies by a simple electrofusion technique induced by ac pulses
Authors: Takahashi Y. , Suzuki K. , Niimura T. , Kano T. , Takashima S. 
Published: December 2004

AbstractA simple and effective technique of electrofusion of the mouse myeloma cells and lymphocytes induced by AC pulses was investigated. Instead of pearl chain formation, we used a mild centrifugation of high‐density cell suspensions to enhance the cell–cell contacts. The optimal frequency of the AC field used for cell fusion was 10 kHz. We confirmed the production of monoclonal antibodies against human serum albumin (HSA) by the hybridoma obtained by this method. Under the conditions used in the present work, the efficiency of hybridoma formation is several times higher than those obtained by the chemical method using polyethylene glycol (PEG). Hybridoma colonies were detected in as high as 95% of the wells and 33% of them proved positive against HSA.
Modeling fermentations with recombinant microorganisms: Formulation of a structured model
Authors: Nielsen Jens , Pedersen Annemarie G. , Strudsholm Kim , Villadsen John 
Published: December 2004

AbstractA simple structured model is described and compared with experimental data for fermentations with recombinant. Escherichia coli. The model is a so‐called compartment, model, where the different biomass components are lumped together in a few intracellular variables. The model is able to describe, in a biologically reasonable fashion, a majority of the observations that have been made through fermentations with recombinant microorganisms. The model is especially suited for description of dynamic changes in plasmid copy number, e.g., runaway plasmid replication.
Calcium and phosphate effects on growth and alkaloid production in Coffea arabica: Experimental results and mathematical model
Authors: Bramble Joye L. , Graves David J. , Brodelius Peter 
Published: December 2004

AbstractPlant, mammalian, and microbial cells are commonly immobilized in calcium alginate gels for the production of valuable secondary metabolites. However, calcium ions are known to inhibit growth in various types of cells, and calcium is an integral part of such gels. Therefore, an investigation was conducted to evaluate the effect of calcium on the growth and alkaloid production of a model cell‐line, Coffea arabica, in suspension culture before, attempting to immobilize such cells in alginate. A kinetic model was then developed from the results to describe cell growth and alkaloid production and the mechanism by which calcium influences these variables. In addition, it was observed that there was a characteristic relationship between the concentration of calcium in the external medium and the concentration of extra cellular and intracellular phosphate. The intracellular phosphate level was, in turn, related to the production of alkaloids. Using these results, a dynamic mathematical model of cell growth and alkaloid production was developed based on the proposed roles of calcium and phosphate. The model showed satisfactory agreement with three sets of experiments at different calcium concentrations. A possible linkage between the calcium and phosphate results is postulated based on the limited solubility of calcium phosphate.
Structured modeling of a microbial system: III. Growth on mixed substrates
Authors: Nikolajsen Karin , Nielsen Jens , Villadsen John 
Published: December 2004

AbstractA two‐compartment model is extended to describe growth and product formation on a mixture of different carbohydrate sources. The open‐ended structure of the compartment model is utilized to include description of the basic mechanisms of catabolite repression. The model is used to simulate batch triauxic, steady‐state, and transient fermentation, and the simulations are compared with experimental results obtained with growth of the lactic acid bacteria Streptococcus cremoris on mixtures of glucose, galactose, and lactose. The model adequately describes characteristic experimental observations such as substrate preference and carbohydrate adoption.
Characterization of a pilot plant airlift tower loop reactor: III. Evaluation of local properties of the dispersed gas phase during yeast cultivation and in model media
Authors: Fröhlich S. , Lotz M. , Larson B. , Lübbert A. , Schügerl K. , Seekamp M. 
Published: December 2004

AbstractThe local properties of the dispersed gas phase (gasholdup, bubble diamater, and bubble velocity) were measured and evaluated at different positions in the riser and downcomer of a pilot plant reactor and, for comparison, in a laboratory reactor. These were described in Parts I and II of this series of articles during yeast cultivation and with model media. In the riser of the pilot plant reactor, the local gas holdup and bubble velocities varied only slightly in axial direction. The gas holdup increased considerably, while the bubble velocity increased only slightly with aeration rate. The bubble size diminished with increasing distance from the aerator in the riser, since the primary bubble size was larger than the equilibrium bubble size. In the downcomer, the mean bubble size was smaller than in the riser. The mean bubble size varied only slightly, the bubble velocity was accelerated, and the gas holdup decreased from top to bottom in the downcomer. In pilot plant at constant aeration rate, the properties of the dispersed phase were nearly constant during the batch cultivation, i.e., they depended only slightly on the cell concentration. In the laboratory reactor, the mean bubble sizes were much larger than in the pilot plant reactor. In the laboratory reactor, the bubble velocities in the riser and downcomer increased, and the mean gas holdup and bubble diameter in the downcomer remained constant as the aeration rate was increased.
Kinetic data for the BM‐5 insect cell line in repeated‐batch suspension cultures
Authors: Stavroulakis Dimitrios A. , Kalogerakis Nicolas , Behie Leo A. , Latrou Kostas 
Published: December 2004

AbstractThe kinetics and growth characteristics of the BM‐5 insect cell line of Bombyx mori (silkworm) have been experimentally investigated in order to develop optimal growth protocols when these cells are used to produce large quantities of human proteins by recombinant baculoviruses. Experiments were performed in 200‐mL spinner flasks, which were operated at 80 rpm with 0.3% methyl cellulose (MCL) added to the medium to protect the cells from shear stress. Exposure of the cells to varying nutrient and metabolite concentrations was accomplished through a repeated‐batch mode of feeding. The results indicate that glutamine is a limiting nutrient and that lactate has an inhibitory effect on cell growth. Ammonia depletion from the medium was accompanied by uric acid accumulation suggesting that ammonia is converted to this metabolic product by the “uricotelic” and “nucleicolytic” metabolic pathways. With the examined medium formulation, glucose, fructose, and sucrose remained at high concentrations throughout the cultivation period.
Enzymic hydrolysis of lignocellulosic materials: I. Models for the hydrolysis process — a theoretical study
Authors: Vallander Lars , Eriksson Karl‐Erik L. 
Published: December 2004

AbstractAt the end of an enzymic hydrolysis process involving a solid lignocellulosic substrate, enzymes are found both in solution and absorbed to the substrate residue. Removal of residue from the system will result in loss of some of the enzymes, the extent of which will depend on the design of the process. To minimize enzyme loss, a study has been conducted in which six process models have been formulated and an enzyme loss function derived for each model based on the total amount of enzymes lost through residue removal. Model 1 is a reference model, characterized by an uninterrupted hydrolysis throughout the entire hydrolysis period. The residue is then washed in order to recover both sugar and adsorbed enzymes before the residue is discarded. Models 2–6 are all characterized by the removal of hydrolysate three times during the process, recirculation of dissolved and adsorbed enzymes to various points in the process and selection of a stage at which the residue is removed. The following conclusions could be drawn from the derived enzyme loss functions:

Increased enzyme adsorption leads to increased enzyme loss.
The enzyme loss decreases if the solid residue is removed late in the process.
Both adsorbed and dissolved enzymes should be introduced at the starting point of the process. This is particularly important for dissolved enzymes. Three models were chosen for experimental studies, which are reported in a second, accompanying article. The experimental results obtained are compared with the theoretical study reported here.