bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of κ‐Carrageenan Gels Used for Immobilization of Bacillus firmus
Authors: Moon Seung‐Hyeon , Parulekar Satish J
Published: March 2005

In this study, aimed at a biochemical and physical characterization of κ‐carrageenan gels used for entrapment of Bacillus firmus NRS 783 (a superior producer of an alkaline protease), effects of carrageenan concentration, gelation temperature, initial cell loading, and strength of the curing agent (KC1) on the properties of cell‐free and cell‐laden gels were examined. The physical properties of the differently prepared gels that were examined included density, free volume fraction, mechanical strength, and change in gel volume during gel curing. The biochemical characteristics studied included viability of gel‐entrapped cells, cell leakage from cell‐laden gels, and cell penetration into cell‐free gels. For the range of carrageenan contents investigated [between 2 % and 5 % (w/v)], the mechanical strength of the gels with/without KC1 curing was observed to increase with an increase in carrageenan content of gels. The mechanical strength of each gel increased substantially upon extensive curing. Free volume fractions in excess of 0.8 were observed for all gels. Of cells that were viable prior to immobilization, 90–92 % remained viable after formation and extensive curing of gels for cell‐gel mixtures prepared at 45°C. Attempts at prolonged storage of cell‐laden gel beads at 0°C as stock cultures of immobilized B. firmus were unsuccessful due to a significant decline in cell viability during such storage. On the basis of the cell leakage studies, the average pore sizes of 2%, 3%, 4%, and 5% gels were deduced to increase in the following order of carrageenan content (w/v): 4%, 3%, 2%, and 5%. Commensurate with the decrease in the average pore size (or the increased tightness of the gels) with increasing carrageenan content, both the extent of cell leakage and the extent of net cell penetration decreased with increasing carrageenan content for the first three gels. Owing to nonuniform distribution of free space and much larger pores, the extent of net cell penetration in 5% carrageenan gels was considerably low, while the extent of cell leakage in 5% carrageenan gels was an order of magnitude greater than the extents of cell leakage in the other three gels.
Hemacytometer Cell Count Distributions: Implications of Non‐Poisson Behavior
Authors: Nielsen Lars K , Smyth Gordon K , Greenfield Paul F
Published: March 2005

The variance of observed cell counts using a hemacytometer was analyzed. The variance was found to be greater than expected under the normally assumed Poisson distribution because of variations in the volume of the counting area. Furthermore, counts from the two sides of the hemacytometer were found to be correlated. Total cell count on a hemacytometer was better described using a normal distribution with quadratic variance, N(λ,λ + σλ2), with σ=0.012. Because hemacytometer cell counts are not Poisson distributed, modified counting protocols are recommended.
Topical Paper: Modeling Transport Processes in Sterilization‐in‐Place
Authors: Noble Paul T.
Published: March 2005

SIP (sterilization‐in‐place) of equipment using saturated steam is limited by transport processes that restrict the distribution of sterilizing steam. The following are two crucial operations: the removal of air prior to sterilization, and the removal of condensate during the sterilization. Using simple model systems of pipes and tanks, characteristic operating parameters were examined and steady‐state models were analyzed. The results were used to evaluate design aspects of SIP, including heat insulation, spacing of steam traps, sloping of lines, steam velocities and consumption, placement of temperature sensors, and scale factors in piping. A more reliable SIP design is achievable by insulating equipment, spacing steam traps to limit condensate buildup, providing an effective air removal operation, and providing reliable, high‐quality steam.
Effect of Oxygen Supply on the Suspension Culture of Genetically Modified Tobacco Cells
Authors: Gao Jianwei , Lee James M.
Published: March 2005

The effect of oxygen supply on the cultivation of the genetically modified tobacco cells and the formation of a foreign protein, β‐glucuronidase (GUS), was investigated in 250‐mL Erlenmeyer flasks, a 5‐L stirred tank fermenter, and a 7‐L air‐lift fermenter. The oxygen supply was varied by using different volumes of medium in the case of the 250‐mL Erlenmeyer flask culture or by the different aeration rate in the case of the two types of fermenters tested. Higher oxygen supply stimulated cell growth and increased oxygen consumption rate, the level of phenolics, and GUS productions.
Escherichia coli Host Cell Modifications in Continuous Culture Affecting Heterologous Protein Overproduction: A Population Dynamics Study
Authors: Fu Jeffrey , Togna A. Paul , Shuler Michael L. , Wilson David B.
Published: March 2005

There are many published studies of plasmid segregational instability in Escherichia coli in the literature. However, the formation of plasmid‐free segregants can be controlled by the addition of selective chemical agents like antibiotics. This solution has become commonplace in both the laboratory and industry. On the other hand, host cell modifications, which result in low production of plasmid‐encoded protein and lead to loss of culture productivity, have not been adequately addressed. Continuous culture of an inducible (ptac) Escherichia coli vector containing strain, RB791(pKN), was characterized by strong dynamic changes in the cell population and product (β‐lactamase) expression. Long‐term cultivation resulted in the loss of high‐level production ofβ‐lactamase. Loss of productivity was not due to the formation of plasmid‐free cells or structural modifications to the plasmid; instead, continuous operation resulted in a culture dominated by irreversibly altered, low‐producing cells. Two distinct classes of lac− mutants which inhibited induction were identified (Y− and Is).
Consistency Evaluation of Batch Fermentations Based on On‐Line NADH Fluorescence
Authors: Kwong Simon C. W. , Randers Lisa , Rao Govind
Published: March 2005

The profiles of on‐line NADH fluorescence as well as the profiles of NADH fluorescence versus dry cell weight (DCW) were used to compare the results of multiple batch fermentations. On the basis of off‐line kinetic parameter analyses, the results indicate that on‐line NADH fluorescence can be used to evaluate the consistency of the results of duplicate batch fermentations.
In Situ Studies of Protein Conformation in Supercritical Fluids: Trypsin in Carbon Dioxide
Authors: Zagrobelny Joann , Bright Frank V.
Published: March 2005

The conformation of the monomeric enzyme trypsin has been studied in supercritical carbon dioxide. Steady‐state fluorescence spectroscopy is used to follow the conformation of trypsin in situ as a function of CO2 density. Our results show for the first time that protein denaturation can occur during the fluid compression step and that the native trypsin is only slightly more stable (1.2 kcal/mol) than the unfolded form. These results demonstrate the power of fluorescence spectroscopy as a tool for studying protein conformation and dynamics in supercritical fluids.
Perfluorooctyl Bromide Dispersions in Aqueous Media for Biomedical Applications
Authors: Habif Stephane S. , Normand Pascal E. , Oleksiak Christian B. , Rosano Henri L.
Published: March 2005

In studying perfluorooctyl bromide (PFOB) dispersions in aqueous media, we have used two types of surfactant: egg yolk phospholipids (EYP) and polyglycerol esters (PGE). Our interest in these dispersions arises from their potential biomedical applications as imaging solutions and oxygen‐carrying solutions (i.e., blood substitutes). For EYP systems, we have identified the dispersion structure as consisting of (a) PFOB droplets (250‐nm diameter) stabilized by a phospholipid monolayer adsorbed irreversibly at the o/w interface and (b) small empty phospholipid vesicles. With both surfactants commercial preparations yielded stable systems, while purified samples, being non‐dispersible, could not be made to act as emulsifiers. In both cases, minor components in the commercial surfactant were found to be necessary for the formation of a stable dispersion, enabling the transport of the pure surfactant to the PFOB/water interface.
Optimizing the Sample Size and the Reduced Velocity To Achieve Maximum Production Rates of Enantiomers
Authors: Jacobson Stephen C. , Felinger Attila , Guiochon Georges
Published: March 2005

Optimum experimental conditions are predicted for the maximum production rate of D‐ or L‐alanine, purified to a 99% purity from a racemic mixture of their N‐benzoyl derivatives by preparative chromatography on ionically immobilized bovine serum albumin. The experimental production rates and recovery yields measured under these conditions are in excellent agreement with the calculated values. These results validate the approach used for optimization of preparative liquid chromatography.
Effect of Protein Adsorption on the Transport Characteristics of Asymmetric Ultrafiltration Membranes
Authors: Mochizuki Seiichi , Zydney Andrew L.
Published: March 2005

The effects of bovine serum albumin adsorption on the transport characteristics of asymmetric poly(ether sulfone) ultrafiltration membranes were determined using polydisperse dextrans with gel permeation chromatograhy. Actual dextran sieving coefficients were evaluated from observed sieving data for both the clean and preadsorbed membranes using a stagnant film model. The flux dependence of the actual dextran sieving coefficients was used to evaluate the intrinsic membrane hindrance factors for convective (i.e., sieving) and diffusive transport for the different molecular weight dextrans using classical membrane transport theory. Protein adsorption caused a reduction in both dextran sieving and diffusion, with the magnitude of the reduction a function of the dextran molecular weight and pore size. The effects of adsorption on the specific pore area and the membrane porosity were then determined using a recent model for solute transport through asymmetric ultrafiltration membranes. The data indicate that protein adsorption occurs preferentially in the larger membrane pores, causing a greater reduction in solute sieving compared to the membrane hydraulic permeability and porosity than would be predicted on the basis of either a simple pore blockage or pore constriction model.
Effects of Plasmid Copy Number and Runaway Plasmid Replication on Overproduction and Excretion of β‐Lactamase from Escherichia coli
Authors: Paul Togna A. , Shuler Michael L. , Wilson David B.
Published: March 2005

Runaway plasmid replication can be used to increase target gene dosage and thereby overproduce proteins within the bacterium Escherichia coli. However, the presence of excessive plasmid DNA often alters normal cell functions. High copy number plasmids with strong promoters place a severe metabolic burden on the cell, causing a decreased specific growth rate and changes in cell physiology. Induction of β‐lactamase synthesis from the tac promoter on plasmid pKN causes runaway plasmid replication and excretion of β‐lactamase. Runaway plasmid relication results from readthrough of tac promoter transcripts into the replication region of the plasmid. Both high plasmid copy numbers and a strong promoter (tac) are necessary to achieve the level of overproduction necessary for excretion of β‐lactamase, but high‐level target protein synthesis is detrimental to the cell. A derivative of pKN which is more easily regulated was constructed by adding the lacl gene to the plasmid.
Simultaneous Biodegradation of Toluene and p‐Xylene in a Novel Bioreactor: Experimental Results and Mathematical Analysis
Authors: Lee Jang‐Young , Choi Yong‐Bok , Kim Hak‐Sung
Published: March 2005

Simultaneous biodegradation of toluene and p‐xylene was performed in a novel bioreactor, and the performance was analyzed on the basis of both experimental and mathematical simulation results. The novel bioreactor employed a silicon tubing as a supplier of the aromatic solvents to be treated, and the transfer rate of toluene and p‐xylene into the culture broth was easily controlled. Batch, sequencing batch, and continuous mode of operation were carried out in the novel bioreactor to compare the performance of the biodegradation of solvent mixture. Sequencing batch operation worked well, but several operational difficulties were found. Continuous operation was shown to present higher biodegradation rates and operational stability. The continuous biodegradation process was mathematically simulated, and operational conditions were optimized on the basis of the simulation results.
Bioprocess Monitoring of Dissolved Oxygen Using a Computerized Pulsing Membrane Electrode
Authors: Chen Jyh‐Chern , Wang Henry Y.
Published: March 2005

A membrane oxygen electrode usually suffers from long‐term signal deterioration due to environmental factors such as changes in hydrodynamic conditions and alteration of membrane oxygen diffusivity due to fouling. These problems can theoretically be overcome by the use of the same oxygen electrode in a pulsing mode. The effects of stirring rate, viscosity of the culture media, and addition of antifoam agents on the direct reading of this pulsing oxygen electrode were investigated, and the results were compared to the traditional pseudo‐steady‐state operation of the electrode. With a pulsing period controlled at 1 s and a rest period of longer than 5 min, the transient signal obtained can be quite stable, and it showed minimal interference from various environmental changes. Dissolved oxygen tension of a cephalosporin C fermentation was monitored using both this pulsing and the conventional pseudo‐steady‐state methods, and their readings were compared to those measured from an off‐line newly calibrated oxygen electrode. The reading from the pulsed electrode showed more favorable agreement with that of the off‐line measurement. The error encountered in using the conventional method of dissolved oxygen measurement could vary as much as 40% in comparison with the actual dissolved oxygen tension during a fermentation process.
Real‐Time Measurement of Anchorage‐Dependent Cell Adhesion Using a Quartz Crystal Microbalance
Authors: Gryte David M. , Ward Michael D. , Hu Wei‐Shou
Published: March 2005

An in situ technique based on the mass‐sensitive piezoelectric quartz crystal microbalance (QCM) was applied to continuously monitor the attachment and detachment of anchorage‐dependent mammalian cells on a metal surface. Specifically, we have demonstrated that the attachment of Vero cells to metal surfaces on the piezoelectrically active area of the QCM results in decreases in the QCM resonant frequency that can be monitored conveniently in real time. Lysis and detachment of Vero cells caused by vesicular stomatitis virus (VSV) infection can also be monitored readily. Our results demonstrate that the QCM is a viable technique for monitoring anchorage‐dependent cell attachment and detachment on surfaces (caused by stimulatory, inhibitory, or cytopathic effects).
Specialized Ribosomes in Escherichia coli
Authors: Leipold Robert J. , Dhurjati Prasad
Published: March 2005

Specialized ribosomes, developed by de Boer and co‐workers at Genentech, carry a mutation in the anti‐Shine—Dalgarno region of 16 S ribosomal RNA, the site of messenger RNA binding. A complementary mutation in the ribosome binding site (the Shine—Dalgarno region) of a particular messenger RNA results in specific and efficient translation of that messenger RNA on the specialized ribosomes. With this system, a fraction of the cell's ribosomes can be dedicated to the translation of a single messenger RNA; the remaining wild‐type ribosomes carry out the normal cellular translation processes. Specialized ribosomes have been used for the overproduction of proteins, analysis of the feedback regulation of ribosomal RNA synthesis, and mutational analysis of 16 S ribosomal RNA. Experimental results related to each of these topics are summarized and discussed, and other potential applications are described. In particular, we propose a novel technique for mutational analysis of 23 S ribosomal RNA, the primary RNA constituent of the large ribosomal subunit, using the specialized ribosome approach.
Interaction of Mercuric Ions with the Bacterial Growth Medium and Its Effects on Enzymatic Reduction of Mercury
Authors: Chang Jo‐Shu , Hong Juan , Ogunseitan Oladele A. , Olson Betty H.
Published: March 2005

The interaction of Hg2+ with components of Luria‐Bertani broth (LB), used to grow the mercury‐resistant strain Pseudomonas aeruginosa PU21 (Rip64), was studied using cold vapor atomic absorption spectrometry and liquid scintillation counting. The time course analysis of free Hg2+ and total Hg in LB solutions showed that 30–40% of Hg2+ formed complexes with tryptone and yeast extract within 140 h. Media containing free or complexed Hg2+ were treated with cell‐free mercuric reductase as well as with growing cells to investigate the effect of the Hg2+‐LB interaction on mercury reduction. In both assays, it was found that the complexed Hg2+ could not be reduced by mercuric reductase or P. aeruginosa PU21 (Rip64).
Cellulose Derivatives with Low Degree of Substitution. 3. The Biodegradability of Cellulose Esters Using a Simple Enzyme Assay
Authors: Glasser Wolfgang G. , Mccartney Bruno K. , Samaranayake Gamini
Published: March 2005

The biodegradability of cellulose ester derivatives using a degradation assay based on commercially available cellulolytic enzyme preparations was found to depend on two factors: degree of substitution (DS) and substituent size. The esters comprised a series of novel and unusual cellulose derivatives, different in both type of substitution and DS, and were prepared using homogeneous phase reaction conditions. The cellulose esters had acyl substituents ranging in size between propionyl and myristyl and DS values between 0.1 and nearly 3. Biodegradation was assayed by incubation with cellulolytic enzymes from two commercial sources followed by the determination of the concentration of reducing sugars. The rate of cellulolytic enzyme biodegradability (CEB) was found to differ with morphology. Two of three parent cellulose preparations and all cellulose products regenerated from homogeneous phase solution reached 75–80% of their maximum degradability within ca. 7 days of incubation with the enzyme system. The maximum degree of acylation (a) which the enzyme could tolerate before the polymer became undegradable and (b) which resulted in degradation in excess of 10% by weight ranged from 0.5 to at least 1.0 of a possible maximum of 3, depending on ester type. CEB per unit of DS was inversely related to the number of carbons present in the acyl substituent.
Lipoprotein Lipase Immobilization onto Porous Chitosan Beads
Authors: Itoyama Koki , Tokura Seiichi , Hayashi Toshio
Published: March 2005

Lipoprotein lipase (LPL) was covalently immobilized onto the surface of porous chitosan beads (ChB) without or with spacers of different lengths. The relative activity (RA) of the immobilized LPL was found to be high toward a small ester substrate, p‐nitrophenyl laurate (pNPL). LPL immobilized with spacer gave an almost constant activity, in marked contrast with the immobilized LPL without spacer, whose activity decreased with decreasing surface concentration. Further, the RA of LPL immobilized with spacer was higher than that of LPL immobilized without a spacer. The pH, thermal, and storage stabilities of the immobilized LPL were higher than those of the free one. LPL immobilized directly to the surface of ChB without any spacer gave a higher stability than that immobilized with spacer, in spite of the lower RA. The spacer effect on RA could be explained in terms of the mobility of the immobilized LPL molecule.
Counteracting Flow Electrophoresis: A Technique for Separating Biochemicals or Charged Macromolecules
Authors: Shea Lonnie D. , Feke Donald L. , Landau Uziel
Published: March 2005

A method for fractionating solutions of charged biochemicals or macromolecules is described. The technique, entitled counteracting flow electrophoresis (CAFE), utilizes parallel electric and fluid flow fields applied within a porous solid barrier to accomplish a separation based on differences in the electrophoretic mobility of the dissolved molecules. A prototypical separation of hemoglobin from bovine serum albumin demonstrated the recovery of a 90+% pure protein with a 20% yield. Improvements in both purity and yield are discussed in terms of barrier characteristics and the intensities of the electrical and flow fields. Barrier characteristics that strongly affect the separation are pore size and thickness.
Sucrose Conversion by Immobilized Invertase in a Multiple Air‐Lift Loop Bioreactor
Authors: Bakker Wilfried A. M. , Knitel Joost T. , Tramper Johannes , De Gooijer Cornells D.
Published: March 2005

A new bioreactor series within one vessel, the multiple air‐lift loop reactor (MAL), is introduced. In the MAL, a series of air‐lift loop reactors is incorporated into one vessel. From residence time distribution studies, it was shown that the three‐compartment MAL behaves as a series of three ideal mixers. A continuously operated MAL, containing immobilized invertase as a model biocatalyst, was evaluated. The advantage of approaching plug flow by using a bioreactor cascade could be shown by comparing substrate conversion in the three‐compartment MAL to that in a single vessel at the same overall dilution rate. This was done for two sets of experimental conditions, which were chosen by using a previously developed model. Intrinsic kinetic parameters of the immobilized enzyme, needed for the model calculations, were determined experimentally. Model calculations gave good approximations of the results. The model incorporates external mass‐transfer resistance and diffusion and reaction in the biocatalyst beads.
Carbon Flux Distributions at the Glucose 6‐Phosphate Branch Point in Corynebacterium glutamicum during Lysine Overproduction
Authors: Vallino Joseph J. , Stephanopoulos Gregory
Published: March 2005

Analyses indicate that the lysine yield in Corynebacterium glutamicum is limited by suboptimal flux partitioning at either the glucose 6‐phosphate (Glc6P), phosphoenolpyruvate (PEP), or pyruvate (Pyr) branch points (or a combination thereof), which results in disproportionate production of the required lysine precursors. Suboptimal flux partitioning at a metabolic branch point can result from the inadequate enzyme activity of a subordinate branch (a weakly rigid branch point) or from the active feedback regulation of the flux partitioning (strongly rigid branch point). In order to examine branch‐point characteristics, we have utilized metabolite balances, constrained by biochemistry, to estimate flux distributions in the primary metabolic network of C. glutamicum from measured, extracellular, metabolite accumulation rates. These flux distributions, in combination with local metabolic perturbations, were used to infer branch‐point characteristics. This study examines the flexibility of the Glc6P branch point, which could limit lysine yield via inadequate NADPH production, by perturbations induced from attenuation of Glc6P isomerase activity (first branch‐point enzyme of glycolysis) and by fermentation on gluconate, which effectively bypasses the Glc6P branch point. Results from the analyses of these perturbations, as well as the flux distributions at the Glc6P branch point during the different phases of a control lysine fermentation, indicate that the Glc6P branch point is neither weakly nor strongly rigid, so that limitations in lysine yield must result from rigidity at either the PEP or Pyr branch point.
Modification of Lipase with Various Synthetic Polymers and Their Catalytic Activities in Organic Solvent
Authors: Ito Yoshihiro , Fujii Hajime , Imanishi Yukio
Published: March 2005

A new enzyme modification has been devised where various vinyl monomers were graftpolymerized using enzyme‐containing aliphatic azo groups as initiators. Thus, an enzyme, lipase, which is not soluble in organic solvents, was made soluble in organic solvents. The modified enzyme catalyzed the esterification reaction in chloroform. Catalytic activity in chloroform was obtained by modification with amphiphilic polymers, such as poly(N‐vinylpyrrolidone), as well as hydrophobic polymers, such as polystyrene and poly (methyl methacrylate). The catalytic activities of the hybrid enzymes increased linearly with increased solubility in chloroform. The hybrid enzymes were thermally stable and used repeatedly.
Ammonium‐Mediated Reduction of Plasmid Copy Number and Recombinant Gene Expression in Escherichia coli
Authors: Vila Pau , Corchero José L. , Benito Antoni , Villaverde Antonio
Published: March 2005

The effect of ammonium as a medium supplement on plasmid‐encoded recombinant β‐galactosidase synthesis was explored in Escherichia coli cells during aerobic growth in complex medium. After induction, only doses of ammonium chloride below 1 g/L are able to transiently enhance the yield. However, the presence of nontoxic ammonium chloride concentrations of up to 10 g/L results in lower values of β‐galactosidase in a concentration‐dependent fashion. A significant reduction in plasmid DNA content explains the decrease in the yield by a gene‐dosage‐involving mechanism.
Pellet Formation and Fragmentation in Submerged Cultures of Penicillium chrysogenum and Its Relation to Penicillin Production
Authors: Nielsen Jens , Johansen Claus L. , Jacobsen Michael , Krabben Preben , Villadsen John
Published: March 2005

The spores of Penicillium chrysogenum are of the noncoagulating type, and after spore germination a culture of disperse mycelia is obtained. In this study, it is shown that when the hyphal elements increase in size, they may agglomerate, and depending on the operating conditions, these agglomerates may develop into pellets with a dense core. The influence of initial spore concentration and agitation rate on agglomeration, leading to pellet formation, was studied. For a low concentration of spores in the inoculum, only a few hyphal elements agglomerate and pellets with a small diameter are obtained. At higher spore concentrations, many hyphal elements agglomerate and develop into large diameter pellets. Finally, at a very high spore concentration in the inoculum, the final hyphal element size is small and agglomerates therefore are not formed. With a high agitation rate, the agglomeration of hyphal elements is reduced. In a repeated fed‐batch cultivation, where there was a shift from pellet morphology to disperse mycelia, it was found that there is no relation between macroscopic morphology and penicillin production by P. chrysogenum. The morphology was quantified throughout the repeated fed‐batch cultivation, and both the pellet diameter and the concentration of pellets were affected by the agitation rate.
Tissue Engineering of a Bioartificial Pancreas: Modeling the Cell Environment and Device Function
Authors: Tziampazis Evangelos , Sambanis Athanassios
Published: March 2005

Cell‐based implantable artificial tissues are most promising for the long‐term treatment of endocrine diseases, such as diabetes. One type of a bioartificial pancreas device consists of calcium alginate microbeads containing insulin‐secreting cells and is surrounded by a poly(L‐lysine) (PLL) membrane. The membrane is semipermeable, allowing cellular nutrients and metabolites to diffuse through but excluding the antibodies and cytotoxic cells of the host, thus immunoprotecting the cells. The device can be modeled by writing the equations for diffusion of nutrients and metabolites through the polymer and for consumption of the former and productionof the latter by the cells. In this paper, we describe the construction and analysis of such amodel for alginate/PLL microbeads with insulin‐secreting recombinant mouse pituitary AtT‐20 and mouse insulinoma βTC3 cells. Entrapped AtT‐20 cells are a simplified model system, whereas microbeads with βTC3 cells constitute a realistic artificial pancreatic device. Effective diffusivities of key compounds through the polymer with entrapped, inactivated AtT‐20 spheroids were measured first. The kinetics of glucose and oxygen consumption and insulin secretion weremodeled next, and the equations for diffusion and reaction were then combined to describe the entire system. The model was used to compute nutrient and metabolite concentration profiles inbeads and the bead secretory response for different bead sizes and cell loadings. The size andloading necessary for the cells to be well nourished and for the beads to be rapidly responsive to step‐ups and step‐downs of secretion stimuli were evaluated. It was shown that if the cells are hypersensitive to glucose, i. e., they do not shut off secretion at the physiological glucose threshold but at a lower one, so are the microbeads. This work demonstrates the usefulness of mechanistic models with representative parameter values in optimizing the design of artificial tissues and in characterizing aspects of their behavior that are of importance for restoring in vivo function.
Model of a Split‐Flow Airlift Bioreactor for Attachment‐Dependent, Baculovirus‐Infected Insect Cells
Authors: Kumar Arun , Shuler Michael L.
Published: March 2005

A mathematical model of a split‐flow airlift bioreactor using attachment‐dependent, baculovirus‐infected insect cells is presented. The model is structured to predict the dynamics of human secreted alkaline phosphatase (seAP) production, nonoccluded virus (NOV) production, infected cell density, uninfected cell density, and lysed cell density for a variety of infection conditions in the reactor. Infected cells are divided into subpopulations on the basis of the time of initial infection and spatial location within the reactor. The infection rate is modeled as first order in virus concentration at low virus concentrations but zero order at high virus concentrations. NOV and seAP production in each subpopulation is assumed to be dependent on the age of the culture and degree of confluency. The subpopulation growth rate is assumed to be dependent on dissolved oxygen concentration and cell density. Extracellular degradation of seAP is included. Model parameters were estimated independently from the literature on Trichoplusia ni BTI‐TN‐5B1‐4 cells infected with recombinant Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) encoding seAP. Model predictions of seAP production are in reasonable agreement with laboratory scale bioreactor data for multiplicity of infection (MOI) values ranging from 1 to 30. The model predicts that bioreactor protein productivity could be increased significantly by operating at an MOI of 10, an initial cell density of 2.5 × 105 cells/cm2, an area ratio of riser to downcomer of 25:75, and an airflow rate of 100 mL/min.
Kinetic and Stoichiometric Analysis of Hairy Roots in a Segmented Bubble Column Reactor
Authors: Kwok Kian H. , Doran Pauline M.
Published: March 2005

Hairy roots of Atropa belladonna were cultured in a modified 2.5‐L multicompartment bubble column for analysis of growth kinetics, stoichiometry, and atropine production. Average biomass density reached 9.9 g L−1 dry weight after 43 days of batch culture; local root densities in some parts of the vessel were considerably higher, up to 17 g L−1. Bulk mixing in the reactor was very poor: after 14 days of culture, the time taken to reach 95% of the equilibrium value after a concentration pulse in the vessel was 12 min. Growth and specific sugar uptake rates declined continuously throughout the culture even though adequate sugar and nitrogen remained in the medium. The observed biomass yield from sugar was approximately constant at 0.35 g g−1; biomass yields from ammonia and nitrate were 0.44 and 0.35 g mmol−1, respectively. Specific atropine content in the roots varied from 4.1 mg g−1 dry weight at the beginning of the culture to 1.4 mg g−1 after 28 days; 35 mg or 14 mg L−1 atropine was produced over the 43‐day culture period. Biomass composition was represented by the elemental formula CH1.63O0.80N0.13, plus 9.8% (w/w) ash. A balanced stoichiometric equation was developed for hairy root growth; this indicated that 8.3% of carbon supplied to the culture was excreted into the medium as byproducts.
Design of Gas‐Treatment Bioreactors
Authors: Andrews G. F. , Noah K. S.
Published: March 2005

Bioreactors are employed increasingly to remove undesirable components from gas streams and to carry out bioprocesses with gaseous nutrients. The problem is to match the type and detailed design of the bioreactor to the characteristics of the component and the microbial metabolism, in order to meet a given set of process requirements at the lowest possible total cost. The higher the specified fractional removal, the greater the advantage of packed‐bed and bubble‐column reactors in which the gas approaches plug flow. The variation of the gas/Liquid interfacial area with gas flow rate makes bubble columns unsuitable for relatively dilute, insoluble components (e.g., hydrocarbons), but the complete mixing of the liquid is an advantage with more concentrated, soluble components, particularly those (e.g., H2S, SO2) that dissociate in contact with water and may be inhibitory at their equilibrium concentrations. When the component is the carbon/energy source or electron acceptor for metabolism, the amount of viable biomass in the reactor at steady state is limited to the rate of component removal divided by the maintenance requirement of the biomass for the component. However, the volume of water in which this biomass is suspended is a variable to be fixed by the process designer or operator. Thus, a packed‐bed bioreactor may be run as a minimum‐water biofilm reactor (given a film‐forming organism) or as a trickle‐bed reactor containing a dilute cell culture (better when the metabolism requires a soluble nutrient or produces a nonvolatile and inhibitory product). In either case, the optimum operating point, close to the onset of mass‐transfer limitation, can be identified by setting the appropriate definition of the Thiele modulus equal to 1. An analysis based on interpolation between these limiting cases suggests a general definition of the modulus. It can be used in conjunction with mass‐transfer and liquid‐holdup correlations as a guide for selecting the type and size of packing material, operating strategies, and scale‐up procedures, which can then be tested by experiment on particular gas streams.
Effect of Viscosity upon Hydrodynamically Controlled Natural Aggregates of Animal Cells Grown in Stirred Vessels
Authors: Moreira José L. , Santana Paula C. , Feliciano Ana S. , Cruz Pedro E. , Racher Andrew J. , Griffiths J. Bryan , Carrondo Manuel J. T.
Published: March 2005

The effect of medium viscosity upon cell growth and aggregate characteristics of baby hamster kidney (BHK) cells cultivated in stirred tanks was evaluated. Two thickening agents were tested, 9300 MW dextran and a low‐viscosity sodium (carboxymethyl)‐cellulose; both were used in two different sets of experiments: (i) 250 cm3 Wheaton spinner flasks with a ball impeller operated at 45 rpm; (ii) 500 cm3 Corning spinner flasks with a paddle impeller, operated at constant power dissipation (88 cm2 s−3) Aggregate diameter and the fraction of cells in aggregates increased with the increase in viscosity. Power laws were applied to the experimental results. A dependence of aggregate size upon power dissipation of the order of –0.19 and kinematic viscosity of 0.34 and 0.49 for the constant agitation and constant power dissipation tests were obtained, respectively. A model based upon the entire universal‐equilibrium range (i.e., the entire spectrum of isotropic eddies) was used to predict theoretical relationships between the variables studied. The model leads to a power dependence of –0.25 for the energy dissipated in the entire universal‐equilibrium range and between 0.25 and 0.5 for the kinematic viscosity in the viscous dissipation subrange, depending on the energy correlation used; it also gives a good explanation for the dependence of aggregate size on the hydrodynamics of the vessel.
Adsorption of Copper and Chromium by Aspergillus carbonarius
Authors: Al‐Asheh Sameer , Duvnjak Zdravko
Published: March 2005

Aspergillus carbonarius NRC 401121 adsorbs some copper and chromium from their solutions. The amount of the adsorbed metal per unit of biomass increased with a decrease in the biomass concentration. The increases in the initial concentrations of metals and pH of the solutions resulted in an increase in copper and chromium uptake. The optimum temperature for copper uptake was 25 °C. Heating of the biomass prior to utilizing it in the adsorption tests decreased its metal adsorption capacity. Preincubation of the biomass with glucose enhanced the metal adsorption. The optimum glucose concentration in this process was 0.1%.
Growth Enhancement of Anchorage‐Dependent and Anchorage‐Independent Cells by Coimmobilization of Insulin with Poly(allylamine) or Gelatin
Authors: Zheng Ji , Ito Yoshihiro , Imanishi Yukio
Published: March 2005

An anchorage‐dependent cell, mouse fibroblast STO cell and an anchorage‐independent cell, K562 cell, were cultured on a polymer membrane coimmobilized with insulin and adhesion factors, poly(allylamine), and gelatin. The former is cationic and electrostatically (non‐biospecifically) enhances cell adhesion, and the latter is a hydrolyzate of collagen and biospecifically enhances cell adhesion. They were immobilized onto a surface‐hydrolyzed poly(methyl methacrylate) membrane by water‐soluble carbodiimide. The adhesion of both STO and K562 cells was accelerated by the immobilization of poly(allylamine) or gelatin. The insulin immobilization did not affect adhesion of either cell. Although the growth of STO cells was enhanced on the insulin‐immobilized membrane, the growth of K562 cells was not. However, the coimmobilization of insulin and a cell‐adhesion factor accelerated growth of both cells. It was considered that an increased frequency of interaction between the immobilized insulin and the receptor led to the cell growth acceleration.
Chemiluminescence‐Based Inhibition Kinetics of Alkaline Phosphatase in the Development of a Pesticide Biosensor
Authors: Ayyagari Madhu S. , Kanitekar Sanjay , Pande Rajiv , Marx Kenneth A. , Kumar Jayant , Tripathy Sukant K. , Akkara Joseph , Kaplan David L.
Published: March 2005

The use and application of the enzyme alkaline phosphatase in a chemiluminescence assay are discussed. The enzyme catalyzes the hydrolysis of a macrocyclic phosphate compound generating a chemiluminescence signal. On the basis of inhibition of this signal, a methodology for the detection and quantitation of organophosphorus‐based pesticides has been developed. The methodology is studied with alkaline phosphatase in the bulk aqueous phase, and detection of the signal is accomplished by a simple optical setup. Parts per billion level detection of paraoxon and methyl parathion in bulk solutions is achieved. The technique is rapid and sensitive and is applicable to the detection of most organophosphorus‐based pesticides. The results from kinetic studies indicate a mixed type of inhibition of the enzyme by paraoxon and methyl parathion. The detection methodology forms an integral part of a biosensor under development and is adaptable to incorporating optical fibers for remote detection of pesticides.
Can desert dust explain the outgoing longwave radiation anomaly over the Sahara during July 2003?
Authors: Haywood Jim M. , Allan Richard P. , Culverwell Ian , Slingo Tony , Milton Sean , Edwards John , Clerbaux Nicolas
Published: March 2005

Measurements of the top‐of‐the‐atmosphere outgoing longwave radiation (OLR) for July 2003 from Meteosat‐7 are used to assess the performance of the numerical weather prediction version of the Met Office Unified Model. A significant difference is found over desert regions of northern Africa where the model emits too much OLR by up to 35 Wm−2 in the monthly mean. By cloud‐screening the data we find an error of up to 50 Wm−2 associated with cloud‐free areas, which suggests an error in the model surface temperature, surface emissivity, or atmospheric transmission. By building up a physical model of the radiative properties of mineral dust based on in situ, and surface‐based and satellite remote sensing observations we show that the most plausible explanation for the discrepancy in OLR is due to the neglect of mineral dust in the model. The calculations suggest that mineral dust can exert a longwave radiative forcing by as much as 50 Wm−2 in the monthly mean for 1200 UTC in cloud‐free regions, which accounts for the discrepancy between the model and the Meteosat‐7 observations. This suggests that inclusion of the radiative effects of mineral dust will lead to a significant improvement in the radiation balance of numerical weather prediction models with subsequent improvements in performance.
2-Arachidonoylglycerol, an endogenous cannabinoid receptor ligand, induces rapid actin polymerization in HL-60 cells differentiated into macrophage-like cells
Authors: GOKOH Maiko , KISHIMOTO Seishi , OKA Saori , MORI Masahiro , WAKU Keizo , ISHIMA Yoshio , SUGIURA Takayuki
Published: March 2005

Δ9-Tetrahydrocannabinol, a major psychoactive constituent of marijuana, interacts with specific receptors, i.e. the cannabinoid receptors, thereby eliciting a variety of pharmacological responses. To date, two types of cannabinoid receptors have been identified: the CB1 receptor, which is abundantly expressed in the nervous system, and the CB2 receptor, which is predominantly expressed in the immune system. Previously, we investigated in detail the structure–activity relationship of various cannabinoid receptor ligands and found that 2-AG (2-arachidonoylglycerol) is the most efficacious agonist. We have proposed that 2-AG is the true natural ligand for both the CB1 and CB2 receptors. Despite the potential physiological importance of 2-AG, not much information is available concerning its biological activities towards mammalian tissues and cells. In the present study, we examined the effect of 2-AG on morphology as well as the actin filament system in differentiated HL-60 cells, which express the CB2 receptor. We found that 2-AG induces rapid morphological changes such as the extension of pseudopods. We also found that it provokes a rapid actin polymerization in these cells. Actin polymerization induced by 2-AG was abolished when cells were treated with SR144528, a CB2 receptor antagonist, and pertussis toxin, suggesting that the response was mediated by the CB2 receptor and Gi/o. A phosphoinositide 3-kinase, Rho family small G-proteins and a tyrosine kinase were also suggested to be involved. Reorganization of the actin filament system is known to be indispensable for a variety of cellular events; it is possible that 2-AG plays physiologically essential roles in various inflammatory cells and immune-competent cells by inducing a rapid actin rearrangement.
The influence of discrete surface charges on the force between charged surfaces
Authors: Khan Malek O. , Petris Simon , Chan Derek Y. C.
Published: March 2005

The force between two parallel charged flat surfaces, with discrete surface charges, has been calculated with Monte Carlo simulations for different values of the electrostatic coupling. For low electrostatic coupling (small counterion valence, small surface charge, high dielectric constant, and high temperature) the total force is dominated by the entropic contribution and can be described by mean field theory, independent of the character of the surface charges. For moderate electrostatic coupling, counterion correlation effects lead to a smaller repulsion than predicted by mean field theory. This correlation effect is strengthened by discrete surface charges and the repulsive force is further reduced. For large electrostatic coupling the total force for smeared out surface charges is known to be attractive due to counterion correlations. If discrete surface charges are considered the attractive force is weakened and can even be turned into a repulsive force. This is due to the counterions being strongly correlated to the discrete surface charges forming effective, oppositely directed, dipoles on the two walls.
Imaging a reactive resonance in the Cl+CH4 reaction
Authors: Zhang Bailin , Liu Kopin
Published: March 2005

The title reaction has been under extensive experimental and theoretical investigations. Presented here is the experimental evidence suggesting a reactive resonance in this reaction—an intriguing possibility that has been hitherto unsuspected. The initial speculation was inferred from theoretical works in the literature, and subsequent confirmation came from the observed pattern of the angular distributions of the HCl(ν′=1)+CH3(v=0) product pair, when plotted in the angle-collision energy plane. This characteristic pattern proves particularly incisive and universal in revealing the imprint of reactive resonance in experimental observable. The nature of the proposed resonance in this reaction is also elucidated.
An antenna-coupled bolometer with an integrated microstrip bandpass filter
Authors: Myers Michael J. , Holzapfel William , Lee Adrian T. , O’Brient Roger , Richards P. L. , Tran Huan T. , Ade Peter , Engargiola Greg , Smith Andy , Spieler Helmuth
Published: March 2005

We describe the fabrication and testing of antenna-coupled superconducting transition-edge bolometers for use at millimeter wavelengths. The design uses a double-slot dipole antenna connected to superconducting niobium microstrip. Band defining filters are implemented in the microstrip, which is then terminated with a load resistor. The power dissipated in the load resistor is measured by a superconducting transition-edge sensor (TES). The load resistor and TES are thermally well connected and are supported by a silicon nitride substrate. The substrate is suspended by four narrow silicon nitride legs for thermal isolation. The bolometers have been optically characterized and the spectral response is presented. This detector is a prototype element for use in an array designed for studies of the cosmic microwave background polarization.
40
000
pixel
arrays of ac-excited silicon microcavity plasma devices
Authors: Park S.-J. , Chen K.-F. , Ostrom N. P. , Eden J. G.
Published: March 2005

Arrays of (50μm)2 Si microcavity plasma devices, as large as 40000pixels (200×200) with a packing density of 104pixelscm−2, have been operated continuously in 500–900Torr of Ne with ac excitation (5–20kHz). More than two orders of magnitude larger than previously reported microplasma device arrays, 200×200pixel structures produce uniform glow discharges in each pixel, have a power consumption of ∼0.85Wcm−2 for pNe=700Torr and an excitation frequency of 5kHz, and exhibit maximum radiative efficiency for a Ne pressure of pNe≅700Torr and an excitation frequency of 10–15kHz. All arrays examined (10×10→200×200) are characterized by pixel-to-pixel emission intensities constant over the entire array to within ±10%, and no barriers to the successful operation of much larger arrays are apparent.
Evidence for charge-carrier mediated magnetic-field modulation of electroluminescence in organic light-emitting diodes
Authors: Wilkinson John , Davis A. H. , Bussmann K. , Long J. P.
Published: March 2005

Electroluminescence (EL) from organic light-emitting diodes can be surprisingly sensitive (∼20%) to modest magnetic fields B (0–2T). The origin of this magnetic-field effect has not been clearly identified, although the magnetic-field effect in some devices resembles that of delayed fluorescence in anthracene, which originates from magnetic-field-dependent singlet-exciton production via triplet-triplet annihilation (TTA). Here, we test the role of TTA at low magnetic fields (∼80mT) by measuring transient EL and by employing dc drive levels so low that the bimolecular rate of TTA is unimportant. Under these conditions, we find enhancements of EL exceeding 14% at the lowest drives, which excludes TTA-mediated magnetic-field effects and indicates a role for charge-carrier pair states.