bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bioprocess Monitoring of Dissolved Oxygen Using a Computerized Pulsing Membrane Electrode
Authors: Chen Jyh‐Chern , Wang Henry Y. 
Published: March 2005

AbstractA 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

AbstractAn 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

AbstractSpecialized 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

AbstractThe 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

AbstractThe 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

AbstractLipoprotein 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

AbstractA 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

AbstractA 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

AbstractAnalyses 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractCell‐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

AbstractA 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

AbstractHairy 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

AbstractBioreactors 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

AbstractThe 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.