bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of feed zone in fed‐batch fermentations of Saccharomyces cerevisiae
Authors: Namdev Pradyumna K. , Thompson B. G. , Gray Murray R.
Published: December 2004

In production‐scale, fed‐batch fermentations, feed is often added to a single point at the top of the fermentor, which, combined with poor mixing, results in formation of a “feed zone” rich in nutrients. Frequent exposure of the culture to high concentrations of nutrients in the feed zone for sufficient duration can produce unexpected effects on its performance. The effect of the feed zone was evaluated by conducting aerobic fed‐batch fermentations of Saccharomyces cerevisiae with both complex and defined media. The broth was recirculated between a recycle loop and a bench‐scale fermentor, and feed was intermittently added into the recycle loop to simulate the circulation of cells through the feed zone. Experiments were carried out for a range of residence times in the recycle loop from 0.5 to 12 min. Biomass yields from the complex‐media fermentations were not affected by exposure to high nutrient levels in the recycle loop for residence times up to 12 min. Ethanol consumption was reduced by as much as 50% for residence time in the loop up to 3 min. Very long exposure of yeast cells to excess nutrient levels (12 min) gave acetic acid formation. In a defined medium, the simulated feed zone effect increased biomass yield by up to 10%, but had no effect on ethanol levels. This study indicates that the feed zone effect on biomass yield in yeast fermentation, using complex substrates, will be negligible under fully aerobic conditions.
Factors affecting microbial sulfate reduction by Desulfovibrio desulfuricans in continuous culture: Limiting nutrients and sulfide concentration
Authors: Okabe S. , Nielsen P. H. , Characklis W. G.
Published: December 2004

The effects of sulfate and nitrogen concentrations of the rate and stoichiometry of microbial sulfate reduction were investigated for Desulfovibrio desulfuricans grown on lactate and sulfate in a chemostat at pH 7.0. Maximum specific growth rates (μmax), half‐saturation coefficients (Ksul), and cell yield (Yc/Lac) of 0.344 ± 0.007 and 0.352 ± 0.003 h −1, 1.8 ± 0.3 and 1.0 ± 0.2 mg/L, and 0.020 ± 0.003 and 0.017 ± 0.003 g cell/g lactate, respectively, were obtained under sulfate‐limiting conditions at 35°C and 43°C. Maintenance energy requirements for D. desulfuricans were significant under sulfate‐limiting conditions. The extent of extracellular polymeric substance (EPS) produced was related to the carbon: nitrogen ratio in the medium. EPS production rate increased with decreased nitrogen loading rate. Nitrogen starvation also resulted in decreased cell size of D. desulfuricans. The limiting C : N ratio (w/w) for D. desulfuricans was in the range of 45 : 1 to 120 : 1. Effects of sulfide on microbial sulfate reduction, cell size, and biomass production were also ivestigated at pH 7.0. Fifty percent inhibition of lactate utilization occurred at a total sulfide concentration of approximately 500 mg/L. The cell size of D. desulfuricans decreased with increasing total sulfide concentration. Sulfide inhibition of D. desulfuricans was observed to be a reversible process. © 1992 John Wiley & Sons, Inc.
Enhancement effect of water activity on enzymatic synthesis of cephalexin
Authors: Hyun Chang K. , Kim Jung H. , Ryu Dewey D. Y.
Published: December 2004

The effect of water activity (aw) of the reaction medium on the enzymatic synthesis of cephalexin (CEX) from 7‐amino‐3‐deacetoxycephalosporanic acid (7‐ADCA) and D‐α‐phenylglycine methyl ester (PGM) was investigated using the α‐amino acid ester hydrolase enzyme from Xanthomonas citri. It was found that the synthetic activity of the enzyme and the conversion yield were markedly improved when the aw of the reaction medium was lowered to about 0.97. The water activity depressing agents evaluated were glycerol, sucrose, and sorbitol, and the conversion yields were improved up to 170% with 15% glycerol, 230% with 30% sucrose, and 270% with 20% sorbitol, respectively. The extent of favorable effect of aw on the conversion yield was not the same among the aw depressors, probably due to other unknown interactions between the enzyme and depressors. However, optimal aw values corresponding to the maximum conversion yield coincided for all aw depressors used. The conversion yield of CEX showed an increasing trend with increasing aw up to the optimal aw value (0.96–0.97) which corresponds to the maximum conversion yield and a decreasing trend beyond the optimal aw. There appears to be a delicate balance between the hydrolytic reaction of PGM and synthetic reaction of CEX. The increasing aw–[E · PGM] complex and the branched reaction pathway fluxes from [E · PGM] to PG (D‐α‐phenyl glycine) and CEX are balanced in such a way that the maximum CEX conversion yield is obtained at aw value of 0.96–0.97. The aw depressors stabilized the enzyme somewhat, but this positive effect was considered to be only a minor contribution to the substantial yield enhancement. The aw depressor effect on viscosity and in turn the mass transfer rate limitation was ruled out since the change in conversion due to the viscosity change was found to be insignificant. © 1993 John Wiley & Sons, Inc.
Numerical and Monte Carlo simulations of phenolic polymerizations catalyzed by peroxidase
Authors: Ryu Keungarp , McEldoon James P. , Pokora Alexander R. , Cyrus William , Dordick Jonathan S.
Published: December 2004

Numerical and Monte Carlo simulations of horseradish peroxidase–catalyzed phenolic polymerizations have been performed. Kinetic constants for the simulations were fit to data from the oxidation and polymerization of bisphenol A. Simulations of peroxidase‐catalyzed phenolic polymerization were run as a function of enzyme concentration and radical transfer and radical coupling rate constants. Predictions were performed with respect to conversion vs. time and number average molecular weight and polydispersity vs. conversion. It is shown that the enzymatic polymerization of phenols can be optimized with respect to high molecular weights by employing low enzyme concentrations and phenols with low radical coupling rate constants coupled with relatively high radical transfer rate constants. Such phenols may be identified by using linear free energy relationships that relate radical reactivity to electron donating/withdrawing potential of the phenolic substituent. © 1993 John Wiley & Sons, Inc.
A numerical analysis of forces exerted by laminar flow on spreading cells in a parallel plate flow chamber assay
Authors: Olivier Lauri A. , Truskey George A.
Published: December 2004

Exposure of spreading anchorage‐dependent cells to laminar flow is a common technique to measure the strength of cell adhesion. Since cells protrude into the flow stream, the force exerted by the fluid on the cells is a function of cell shape. To assess the relationship between cell shape and the hydrodynamic force on adherent cells, we obtained numerical solutions of the velocity and stress fields around bovine aortic endothelial cells during various stages of spreading and calculated the force required to detach the cells. Morphometric parameters were obtained from light and scanning electron microscopy measurements. Cells were assumed to have a constant volume, but the surface area increased during spreading until the membrane was stretched taut. Two‐dimensional models of steady flow were generated using the software packages ANSYS (mesh generation) and FIDAP (problem solution). The validity of the numerical results was tested by comparison with published results for a semicircle in contact with the surface. The drag force and torque were greatest for round cells making initial contact with the surface. During spreading, the drag force and torque declined by factors of 2 and 20, respectively. The calculated forces and moments were used in adhesion models to predict the wall shear stress at which the cells detached. Based upon published values for the bond force and receptor number, round cells should detach at shear stresses between 2.5 and 6 dyn/cm2, whereas substantially higher stresses are needed to detach spreading and fully spread cells. Results from the simulations indicate that (1) the drag force varies little with cell shape whereas the torque is very sensitive to cell shape, and (2) the increase in the strength of adhesion during spreading is due to increased contact area and receptor densities within the contact area. © 1993 John Wiley & Sons, Inc.
Molecular integrity of monoclonal antibodies produced by hybridoma cells in batch culture and in continuous‐flow culture with integrated product recovery
Authors: Mohan S. B. , Chohan S. R. , Eade J. , Lyddiatt A.
Published: December 2004

The molecular integrity of monoclonal antibodies (MCAB) produced by murine hybridoma cell line TB/C3 was studied in batch and continuous‐flow cultures. In batch culture, one band of MCAB was detected initially by Western blotting of sodium dodecyl sulfate (SDS)–polyacrylamide gels run under unreduced conditions, but heterogenous MCAB bands appeared as the culture aged. The latter were due to the degradation of MCAB by proteases active at the neutral pH of the culture. The deleterious effect of proteases was minimized in the continuous‐flow cultures which were integrated for product recovery. The MCAB of high quality was purified over 26 days from a culture grown at a dilution rate of 0.025 h−1 (experiment 1). However, at a lower dilution rate of 0.015 h−1 (experiment 2), the integrity of MCAB was compromised after the initial 13 days of culture. This was shown to be due to the variation in the carbohydrate content of MCAB produced, as judged by the increased sialylation of heavy chains and the varied reactivity of MCAB with lectins (Maackia amurensis agglutinin, Galanthus nivalis agglutinin, and Datura stramonium agglutinin) as the age of the culture increased. The concentration of the purified MCAB samples by enzyme‐linked immunosorbent assay (ELISA) (used normally) was usually higher than that estimated by absorbance at 280 nm. Best correlation between the two methods (ELISA–280 nm ratio of 1.02–1.25) was obtained with experiment 1 samples. This ratio increased in experiment 2 and batch culture samples as the heterogeneity of MCAB produced increased, being 1.03–2.94 and 2.53–4.62, respectively. Therefore, ELISA overestimated MCAB concentration when the molecular integrity of the latter was compromised. The ELISA–A280 nm ratio might hence provide a useful indicator for assessing the quality of MCAB produced. Comparison of SDS–polyacrylamide gels stained with Coomassie Brilliant Blue R and silver showed that the former correlated better with the MCAB activity stain, whereas the silver stained both the protein‐ and carbohydrate‐rich components. Comparison of the patterns produced with these two stains might therefore offer another parameter to monitor the overall integrity of MCAB produced. Finally, the data presented have important implications on the validity of using long‐term and intensive cultures for generating MCAB because such cultures would be subjected to the additive effects reported for batch and continuous modes of growth. © 1993 John Wiley & Sons, Inc.
Surfactant‐Induced hydrogen production in cyanobacteria
Authors: Famiglietti M. , Hochkoeppler A. , Luisi P. L.
Published: December 2004

Addition of Tween 85 to aqueous suspensions of Anabaena variabilis induced photosynthetic evolution of hydrogen over a time span of several weeks: As much as 148 nmol H2/h · mg dry weight was produced in the first week by a suspension containing 4.2 mg dry weight of cells and 77 mM Tween 85. The chemical structure of Tween 85 was a necessary prerequisite for inducing hydrogen production, as compounds such as Tween 20, 60, and 80 had a quite different effect. There was a coupling between photosynthetic oxygen evolution and hydrogen evolution: Hydrogen evolution started to be effective only when oxygen evolution subdued. The presence of heterocysts in A. variabilis was also required for the Tween‐induced hydrogen production. Based on these observations, possible mechanisms for the photosynthetic effect of Tween 85 are advanced and discussed. © 1993 John Wiley & Sons, Inc.
Immobilization of glucose oxidase in thin polypyrrole films: Influence of polymerization conditions and film thickness on the activity and stability of the immobilized enzyme
Authors: Almeida Nicholas F. , Beckman Eric J. , Ataai Mohammad M.
Published: December 2004

Using monomers that polymerize to form electrically conducting polymers, one can control the thickness of the polymer film and the amount of enzyme that can be immobilized in the films. First, an investigation of the major variables that influence the immobilization of glucose oxidase by entrapment in polypyrrole films, prepared by electropolymerization from aqueous solutions containing the enzyme and monomer, was carried out. Then the optimized conditions were used to assess the effects of film thickness on the activity and stability of immobilized enzyme. For the films ranged in thickness from 0.1 μm to 1.6 μm, the resulting apparent activity and stability of the immobilized enzyme were found to be a strong function of the polymer film thickness. Above a thickness of 1.0 μm, the apparent activity of the immobilized enzyme increases linearly with increasing film thickness. The nonlinearity observed for films of thickness less than 1.0 μm can be attributed to the changes observed in the morphology of the resulting polypyrrole films. Furthermore, it was noted that when the glucose oxidase/polypyrrole films are stored in phosphate buffer, at 4°C, the observed rate of loss in apparent activity of the immobilized enzyme is highest for the first few days, also being higher for the thinner films. However, after the loosely entrapped enzyme is leached from the polymer film, the rate of loss in activity is very low indicating that the well‐entrapped enzyme, as well as the polypyrrole films, exhibit good stability. Finally, the reproducibility of the immobilization technique is excellent. © 1993 John Wiley & Sons, Inc.
Quantification of damage to suspended insect cells as a result of bubble rupture
Authors: Trinh Kim , Garcia‐Briones Miguel , Chalmers Jeffrey J. , Hink Fred
Published: December 2004

It is proposed that when cells are either attached to, or very near, a rupturing bubble, the hydrodynamic forces associated with the rupture are sufficient to kill the cells. Four types of experiments were conducted to quantify the number and location of these killed cells. We determined: (1) the number of cells killed as a result of a single, 3.5‐mm bubble rupture; (2) the number and viability of cells in the upward jet that results when a bubble ruptures; (3) the number of cells on the bubble film; and (4) the fate of cells attached to the bubble film after film rupture. All experiments were conducted with Spodoptera frugiperda (SF‐9) insect cells, in TNM‐FH and SFML medium, with and without Pluronic F‐68. Experiments indicate that approximately 1050 cells are killed per single, 3.5‐mm bubble rupture in TNM‐FH medium and approximately the same number of dead cells are present in the upward jet. It was also observed that the concentration of cells in this upward jet is higher than the cell suspension in TNM‐FH medium without Pluronic F‐68 by a factor of two. It is believed that this higher concentration is the result of cells adhering to the bubble interface. These cells are swept up into the upward jet during the bubble rupture process. Finally, it is suggested that a thin layer around the bubble containing these absorbed cells is the “hypothetical killing volume” presented by other researchers. © 1994 John Wiley & Sons, Inc.
Enhanced disruption of Candida utilis using enzymatic pretreatment and high‐pressure homogenization
Authors: Baldwin Clark V. , Robinson Campbell W.
Published: December 2004

The enhancement of the overall disruption of a native strain of Candida utilis (ATCC 9226) was studied using a combination of two methods, namely, pretreatment in the form of partial enzymatic lysis by Zymolyase followed by mechanical disruption in a Microfluidizer high‐pressure homogenizer. The cells were grown in both batch and continuous cultures to examine the effect of specific growth rate on disruption. Cell suspensions ranging in concentration from 7 to 120 g DW/L were disrupted with and without enzymatic pretreatment. For yeast grown in batch culture, final total disruption obtained using the combined protocol approached 95% with four passes at a pressure of 95 MPa, as compared with only 65% disruption using only mechanical homogenization. A modified model was developed to predict the fraction disrupted by the enzymatic pretreatment‐mechanical homogenization two‐stage process. Predicted disruptions agreed favorably with experimental observations (maximum deviation of 20%) over a wide range of operating conditions. © 1994 John Wiley & Sons, Inc.
A cellular automaton model for microcarrier cultures
Authors: Hawboldt Kelly A. , Kalogerakis Nicolas , Behie Leo A.
Published: December 2004

In order to achieve high cell densities anchoragedependent cells are commonly cultured on microcarriers, where spatial restrictions to cell growth complicates the determination of the growth kinetics. To design and operate large‐scale bioreactors for microcarrier cultures, the effect of this spatial restriction to growth, referred to as contact inhibition, must be decoupled from the growth kinetics. In this article, a cellular automaton approach is recommended to model the growth of anchorage‐dependent cells on microcarriers. The proposed model is simple to apply yet provides an accurate representation of contact‐inhibited cell growth on microcarriers. The distribution of the number of neighboring cells per cell, microcarrier surface areas, and inoculation densities are taken into account with this model. When compared with experimental data for Vero and MRC‐5 microcarrier cultures, the cellular automaton predictions were very good. Furthermore, the model can be used to generate contact‐inhibition growth curves to decouple the effect of contact‐inhibition from growth kinetics. With this information, the accurate determination of kinetic parameters, such as nutrient uptake rates, and the effects of other environmental factors, such as toxin levels, may be determined. © 1994 John Wiley & Sons, Inc.
Review: Tissue engineering in the nervous system
Authors: Bellamkonda Ravi , Aebischer Patrick
Published: December 2004

The nervous system presents a challenge to the field of tissue engineering because some of its complex neurochemical and neuroanatomical architecture is just beginning to be understood. A combination of advances in molecular neurobiology, gene transfer techniques, and the concomitant advances in the engineering of biomaterials at a molecular level, are making tissue engineering in the nervous system possible. Due to the vast range of fields that this highly interdisciplinary task spans, any review is bound to be somewhat limited. Given that, this review attempts to cover some solutions engineered for: (a) the functional replacement of a missing neuroactive component; (b) the rescue or regeneration of degenerated neural tissue; and (c) the building of intelligent neural cell‐based biosensors and simple in vitro neural circuits based on controlled neural cell attachment to electrically relevant substrates. © 1994 John Wiley & Sons, Inc.
Review: Bone tissue engineering: The role of interstitial fluid flow
Authors: Hillsley M. V. , Frangos J. A.
Published: December 2004

It is well established that vascularization is required for effective bone healing. This implies that blood flow and interstitial fluid (ISF) flow are required for healing and maintenance of bone. The fact that changes in bone blood flow and ISF flow are associated with changes in bone remodeling and formation support this theory. ISF flow in bone results from transcortical pressure gradients produced by vascular and hydrostatic pressure, and mechanical loading. Conditions observed to alter flow rates include increases in venous pressure in hypertension, fluid shifts occurring in bedrest and microgravity, increases in vascularization during the injury‐healing response, and mechanical compression and bending of bone during exercise. These conditions also induce changes in bone remodeling. Previously, we hypothesized that interstitial fluid flow in bone, and in particular fluid shear stress, serves to mediate signal transduction in mechanical loading‐ and injury‐induced remodeling. In addition, we proposed that a lack or decrease of ISF flow results in the bone loss observed in disuse and microgravity. The purpose of this article is to review ISF flow in bone and its role in osteogenesis. © 1994 John Wiley & Sons, Inc.
Long‐Term continuous culture of hepatocytes in a packed‐bed reactor utilizing porous resin
Authors: Miyoshi Hirotoshi , Yanagi Kennichi , Ohshima Norio , Fukuda Hideki
Published: December 2004

As part of our attempt to develop a hybrid artificial liver support system using cultured hepatocytes, we investigated the long‐term metabolic function of hepatocytes incubated in a packed‐bed type reactor using reticulated polyvinyl formal (PVF) resin as a supporting material. Long‐term (up to 1 week) perfusion culture experiments using the packed‐bed reactor (20 mm i.d.) loaded with 500 PVF resin cubes (mean pore size 250 μm, 2 × 2 × 2 mm), together with conventional monolayer culture experiments as controls, were performed in serum‐free or serum‐containing medium. Ammonium metabolism and urea synthesis activities were evaluated quantitatively based on reaction kinetic analyses. Initial rates of ammonium metabolism and urea‐N synthesis, as well as GPT enzyme activities, were adopted as indexes of the metabolic performance of the reactor and activities of the cultured hepatocytes.

When serum‐free medium was used in the perfusion cultures, ammonium metabolic and urea‐N synthetic rates showed significant decay with elapse of the culture period, being less than 10% of those measured on day 1. This loss of activity was more prominent in the perfusion culture than in the monolayer cultures using this medium. In contrast, when serum‐containing medium was used, approximately 50% of these activities obtained on day 1 were maintained even at the end of the cultures both in the perfusion and monolayer culture experiments.

We concluded that the packed‐bed reactor using PVF resin enabled high‐density culture of hepatocytes, and showed a satisfactory ability to maintain the metabolic function of immobilized hepatocytes for relatively long periods of up to 1 week. This type of reactor is thus considered to represent a breakthrough in overcoming the difficulties involved in the development of a hybridtype artificial liver support system. © 1994 John Wiley & Sons, Inc.
Growth of recombinant fibroblasts in alginate microcapsules
Authors: Chang P. L. , Hortelano G. , Awrey D. E. , Tse M.
Published: December 2004

To develop a novel strategy of nonautologous somatic gene therapy, we now demonstrate the feasibility of culturing genetically modified fibroblasts within an immunoprotective environment and the optimal conditions required for their continued survival in vitro. When mouse Ltk− fibroblasts transfected with the human growth hormone gene were enclosed within permselective microcapsules fabricated from alginate–polylysine–alginate, they continued to secrete human growth hormone at the same rates as the nonencapsulated cells. They also continued to proliferate in vitro for at least 1 month even though their viability gradually declined to about 50%. The viability can be improved by controlling for (a) temperature during encapsulation, (b) duration of treatment with polylysine, (c) duration of liquefying the core alginate with sodium citrate, and (d) cell density at the time of encapsulation. The best conditions leading to improved survival and maximum proliferation of cells within the microcapsules were obtained by encapsulating the cells at 4 to 10°C instead of room temperature, coating the microspheres with polylysine for 6 to 10 min instead of 20 min, liquefying the core alginate by treating with citrate for 20 min instead of 6 to 10 min, and using a concentration of 2 × 106 cells/mL of alginate for encapsulation. Under such conditions, normally adherent and genetically engineered mouse fibroblasts survived and proliferated optimally within the microcapsule environment. The encapsulated fibroblasts maintained their level of transgene expression while recombinant gene products such as human growth hormone could diffuse through the microcapsule membrane without impediment. The demonstration that genetically modified fibroblasts can survive and continue to deliver recombinant gene products from within these microcapsules and the optimization for their maximal viability and growth within microcapsules should increase the potential for success in using such microencapsulated recombinant cells for somatic gene therapy. © 1994 John Wiley & Sons, Inc.
Blueprint for a lipase support: Use of hydrophobic controlled‐pore glasses as model systems
Authors: Bosley John A. , Clayton John C.
Published: December 2004

For the commercial exploitation of lipase biocatalysis to be successful, it is essential that effective supports are selected for lipase immobilization. In this study hydrophobic controlled‐pore glasses have been used as model systems for the immobilization of Rhizomucor miehei lipase. The effect of pore diameter and surface chemistry on enzyme efficiency in a typical esterification reaction under essentially nonaqueous conditions has been examined. It has been found that pore diameters of at least 35 nm are needed for the lipase to be able to utilize the internal volume of the support particles in the immobilization process. Despite the small size of the substrates in the esterification reaction, even larger pores (>100 nm) are required for the lipase efficiency to become independent of pore diameter; below 100 nm lipase activity and efficiency are markedly reduced. It has also been shown that the chemical nature of the hydrophobic surface plays an important part in catalyst design. Although lipase will adsorb readily to a wide range of hydrophobic groups, the highest catalyst activities are obtained when the glass surface is derivatized to give long alkyl chains; the presence of unsaturated derivatives gonerally leads to a reduction in activity. © 1994 John Wiley & Sons, Inc.
Kinetics of adhesion and spreading of animal cells
Authors: Ramsden J. J. , Li S.‐Y. , Prenosil J. E. , Heinzle E.
Published: December 2004

The adhesion and spreading of cells at surfaces are well established phenomena which have been extensively observed using light or electron microscopy. The kinetics of both processes can be quantitatively measured by allowing the cells to attach themselves to the surface of a planar waveguide allows the number of cells per unit area and a parameter uniquely characterizing their shape, such as the area in contact with the surface, to be determined. Cells suspended in nutrient medium or pure phosphate buffer were allowed to attach to and spread on a metal oxide surface or a layer of fibronectin, and the kinetics of attachment and spreading have been measured. Attachment kinetics are the same in all cases, but spreading on the metal oxide requires nutrient medium, without which it does not occur. Spreading of cells attached to a layer of fibronectin in the absence of nutrient medium occurs at about a tenth of the rate of cells spreading on metal oxide in the presence of nutrient. © 1994 John Wiley & Sons, Inc.
Surfactant‐Modified lipase for the catalysis of the interesterification of triglycerides and fatty acids
Authors: Basheer Sobhi , Mogi Ken‐ichi , Nakajima Mitsutoshi
Published: December 2004

The lipase‐catalyzed intresterification of triglycerides and fatty acids in n‐hexane was studied. Initially, lipase Saiken was modified with a surfactant of sorbitan esters so that its dispersibility in hydrophobic organic media was improved. The surfactant‐modified lipase formed in the modification process carried out in a buffer solution has 1,3‐positional specificity and predominantly catalyzed the interesterification reaction in a microaqueous n‐hexane system. The modification technique converted inactive lipases to very active biocatalysts for the interesterification of triglycerides and fatty acids. The pH and the weight ratio of surfactant to enzyme used during the lipase modification process have shown significant effects in determining the recoveries of the protein and enzyme activity from the buffer solution, the protein content of the modified lipase complex after being freeze dried, and the interesterification activity of the complex. The water content in the reaction solution has strongly influenced the enzyme activity as well as the distribution of the products. © 1995 John Wiley & Sons, Inc.
Effects of calcium on development of anaerobic acidogenic biofilms
Authors: Huang J. , Pinder K. L.
Published: December 2004

Anerobic biofilms with dominantly acidogenic bacteria were grown in fixed‐bed recycle reactors. The influence of calcium concentration in the culture medium on biofilm mass accumulation, immobilized calcium concentration, and biofilm‐specific activity was investigated. The results indicate that the biofilm mass accumulation was increased by the presence of calcium in the growth medium when calcium concentration was not higher than 120mg/L. Calcium accumulated in the biofilms increased in proportion to the calcium level in the feed. The biofilms for an increased input calcium concentration showed a trend of decrease in specific activity. The biofilms with a thickeness of less than 0.5 mm had the highest specific activity. The optimum calcium concentration for substrate consumption by the biofilms was 100 to 120 mg/L. The biofilms transferred from higher calcium medium to lower calcium medium were more susceptible to sloughing from their support surfaces, which indicates calcium's role in the stability of the biofilm structure. © 1995 John Wiley & Sons, Inc.
Production of poly(D‐3‐hydroxybutyrate) from CO2, H2, and O2 by high cell density autotrophic cultivation of Alcaligenes eutrophus
Authors: Tanaka Kenji , Ishizaki Ayaaki , Kanamaru Toshihisa , Kawano Takeharu
Published: December 2004

Hydrogen‐oxidizing bacterium, Alcaligenes eutrophus autotrophically produces biodegradable plastic material, poly(D‐3‐hydroxybutyrate), P(3HB), from carbon dioxide, hydrogen, and oxygen. In autotrophic cultivation of the microorganism, it is essential to eliminate possible occurrence of gas explosions from the fermentation process. We developed a bench‐plant scale, recycled‐gas, closed‐circuit culture system equipped with several safety features to perform autotrophic cultivation of A. eutrophus by maintaining the oxygen concentration in the substrate gas phase below the lower limit for a gas explosion (6.9%). The culture vessel utilized a baskettype agitator, resulting in a KL a value of 2970 h−1. Oxygen gas was also directly fed to the fermentor separately from the other gases. As a result, 91.3 g · dm−3 of the cells and 61.9 g · dm−3 of P(3HB) were obtained after 40 h of cultivation under this oxygen‐limited condition. The results compared favorably with those reported for mass production of P(3HB) by heterotrophic fermentation. © 1995 John Wiley & Sons, Inc.
Development of optimized transfectoma cell lines for production of chimeric antibodies in hollow fiber cell culture systems
Authors: Schläpfer Beatrice S. , Scheibler Marcel , Holtorf Anke‐Peggy , Van Nguyen Hai , Pluschke Gerd
Published: December 2004

Methods for the selection of transfectoma cells that express large quantities of mouse–human chimeric antibodies have been develped. SP2/0 mouse myeloma cells were transfected with pSV2‐gpt and pSV2‐neo based immunoglobulin expression vectors. Double transfectants were selected using the xanthine–guanine phosphoribosyl transferase (gpt)and the neomycin (neo) selection marker genes. ELISA‐based screening of transfectoma clones resulted in the isolation of IgG‐producing transfectomas. Introduction of the kappa light‐chain 3′‐enhancer into the light‐chain expression vector significantly increased immunoglobulin expression, but only when the enhancer was located at its physiological site, 9 kb downstream of the kappa constant region exon. With some of the transfectomas, final yields of up to 80 mg/L of chimeric IgG were obtained in conventional flask cultures using serum‐free growth medium. A pilot‐scale AcuSyst Maximizer hollow fiber cell culture system was used for the production of gram amounts of chimeric IgG. Results obtained with different transfectoma clones in conventional culture were not fully predictive for yields in the hollow fiber system. In contrast, differences in productivity between individual clones in the laboratory‐scale Tecnomouse cell culture unit were comparable with those in the Maximizer system. Up to 200 mg of chimeric IgG were produced per day in one Maximizer bioreactor. © 1995 John Wiley & Sons, Inc.
Dielectrophoretic separation of cells: Continuous separation
Authors: Markx Gerard H. , Pethig Ronald
Published: December 2004

Dielectrophoresis is the movement of particles in non‐uniform alternating and direct current (AC, DC) electric fields. When nonuniform electric fields are created between microelectrodes, cells will redistribute themselves around the electrodes, the force holding the cells in place dependig on the local electric field and on the electrical properties of the cells themselves and the suspending medium. Steric drag forces produced by a gentle fluid flow in the chamber can be used to separate cells by selectively lifting cells from potential energy wells produced by the electric field. The technique is demonstrated in the batch separation of bacteria, yeast cells, and plant cells. Continuous separation and extraction of two cell types can be achieved by repeated reversing of the fluid flow direction in phase with the switching on and off of the applied voltage, and the efficacy of the technique is demonstrated for viable and nonviable (heat‐treated) yeast cells. © 1995 John Wiley & Sons, Inc.
Development of effective modified cellulase for cellulose hydrolysis process
Authors: Park Jin Won , Kajiuchi Toshio
Published: December 2004

Cellulase was modified with amphilic copolymers made of α‐allyl‐ω‐methoxy polyoxyalkylene (POA) and maleic acid anhydride (MAA) to improve the cellulose hydrolytic reactivity and cellulase separation. Amino groups of the cellulase molecule are covalently coupled with the MAA functional groups of the copolymer. At the maximum degree of modification (DM) of 55%, the modified cellulase activity retained more than 80% of the unmodified native cellulase activity. The modified cellulase shows greater stability against temperature, pH, and organic solvents, and demonstrated greater conversion of substrate than native cellulase does. Cellulase modification is also useful for controlling strong adsorption of cellulase onto substrate. Moreover, cellulase modified with the amphiphilic copolymer displays different separation characteristics which are new. One is a reactive two‐phase partition and another is solubility in organic solvents. It appears that these characteristics of modified cellulase work very effectively in the hydrolysis of cellulose as a total system, which constitutes the purification of cellulase from culture broth, hydrolysis of cellulose, and recovery of cellulase from the reaction mixture. © 1995 John Wiley & Sons, Inc.
Preferential release of one daughter cell during division of immobilized chinese hamster ovary cells
Authors: Helmstetter Charles E.
Published: December 2004

Chinese hamster ovary (CHO) cells were attached to tiny adhesive sites in poly‐2‐hydroxyethyl methacrylate(polyHEMA‐) coated glass, and their divison properties were examined. The adhesive sites were produced by placing a metal mask, containing 8‐μm‐diameter holes arranged in a regular pattern, on top of the coated glass and exposing the sandwich to glow discharge treatment. This treatment produced an ordered array of circular cavities in the polyHEMA down to the glass. These adhesive sites were smaller in diameter than a newborn CHO cell, so that, upon division, there would theoretically be room for only one of the two new daughter cells to remain attached. It was found that individual CHO cells attached to, and grew upon, the sites, and that division normally resulted in the releas of one of the two new daughters. It is concluded that this culture technique has applications in research on the mammalian cell cycle, cell partitioning, and cellular senescence. © 1995 John Wiley & Sons, Inc.
Membrane anchored protein production from spheroid, porous, and solid microcarrier chinese hamster ovary cell cultures
Authors: Kennard M. L. , Piret J. M.
Published: December 2004

The influence of the microcarrier type on the performance of a controlled release process used to produce a recombinant glycosyl‐phosphatidylinositol anchored protein was investigated. Chinese hamster ovary (CHO) cells expressing the human melanoma tumor antigen (p97) were cultured in 10% serum on Cultispher‐GH porous microcarriers and then, for protein production, maintained in 2% serum. Cells were harvested every 48 h and p97 was recovered at 90 μg/mL and 40% purity. Harvested p97 concentrations were increased by harvestingfrom spheroid (241 μg/mL) and smaller porous microcarrier, Cultispher‐G (167 μg/mL) cultures. The low total cell specific p97 production of cells cultured on Cultispher‐GH was due to necrosis of cells within the beads, decreased p97 expression of the immobilized cells, dilution by the liquid (up to 40% volume) associated with settled beads, and incomplete recovery of p97 from within the beads. Cells cultured on solid microcarriers, Cytodex‐1, had the highest cell viability and cell specific p97 production, It is recommended that a two‐stage cyclic harvesting process of cells cultured on small Cultispher‐G or on Cytodex‐1 beads would minimize protein loss and maximize cell specific protein recovery. © 1995 John Wiley & Sons Inc.
Bioleaching of pyrite by acidophilic thermophile Acidianus brierleyi
Authors: Konishi Yasuhiro , Yoshida Shigeyuki , Asai Satoru
Published: December 2004

The kinetics of bioleaching of pyrite (FeS2) by the acidophilic thermophilic bacterium Acidianus brierleyi was studied in a well‐mixed batch reactor. Experiments were done at 65°C and pH 1.5 on adsorption of A. brierleyi onto pyrite particles, liquid‐phase oxidation of ferrous iron by A. brierleyi, and microbial leaching of pyrite. The adsorption of A. brierleyi was a fast process; equilibrium was attained within the first 30 min of exposure to pyrite. The adsorption equilibrium data were well correlated with the Langmuir isotherm. The oxidation of ferrous iron was markedly accelerated in the presence of A. brierleyi, and the growth yield on ferrous iron was determined. The bioleaching of pyrite by A. brierleyi was found to take place with a direct attack by adsorbed cells on the surface of pyrite, the chemical leaching of pyrite by ferric iron being insignificant. Rate data collected under a wide variety of operating variables were analyzed to determine kinetic and stoichiometric parameters for the microbial pyrite leaching. The specific growth rate on pyrite for A. brierleyi was about four times that for the mesophilic bacterium, Thiobacillus ferrooxidans, whereas the growth yields on pyrite for the two microbes were approximately equal to one another in magnitude. A comparison of A. brierleyi with T. ferrooxidans for pyrite leachability demonstrated the thermophile to be much more effective. © 1995 John Wiley & Sons, Inc.
Simultaneous light emission from cloned Vibrio fischeri lux genes and expression of LamB or LamB–protein A fusion proteins in Escherichia coli depends on using a single chimeric operon
Authors: Steidler Lothar , Fiers Walter , Remaut Erik
Published: December 2004

Fusion proteins between LamB and immunoglobulin G binding domains of the Staphylococcus aureus protein A (SPA) have previously been shown to be located in the outer membrane and to convey immunoglobulin binding activity to intact Escherichia coli cells. However, the induced synthesis (tac promoter dependent) of these proteins severely impaired light production from the Vibrio fischeri lux operon present on a compatible plasmid and transcribed from its own control elements. Coordinate inducible expression of both phenomena, light emission and synthesis of LamB or LamB–SPA fusions, could be achieved by construction of artificial operons, joining all but luxl of the rightward lux operon to the 3′ end of the LamB‐spa expression cassettes, under transcriptional control of the tac promoter. Biotechnological applications are discussed. © 1995 John Wiley & Sons, Inc.
Characterization of free and alginate–polylysine–alginate microencapsulated Erwinia herbicola for the conversion of ammonia, pyruvate, and phenol into L‐tyrosine
Authors: Lloyd‐George Ian , Chang T. M. S.
Published: December 2004

The whole cell tyrosine phenol‐lyase (TPL, E.C. 4.1.99.2) activity of Erwinia herbicola (ATCC 21434) was microen‐capsulated. We studied the use of this for the conversion of ammonia and pyruvate along with phenol or catechol, respectively, into L‐tyrosine or dihydroxyphenyl‐L‐alanine (L‐dopa). The reactions are relevant to the development of new methods for the production of L‐tyrosine and L‐dopa. The growth of E. herbicola at temperatures from 22°C to 32°C is stable, since at these temperatures the cells grow up to the stationary phase and remain there for at least 10 h. At 37°C the cells grow rapidly, but they also enter the death phase rapidly. There is only limited growth of E. herbicola at 42°C. Whole cells of E. herbicola were encapsulated within alginate‐polylysine‐alginate microcapsules (916 ± 100 μm, mean ± std. dev.). The TPL activity of the cells catalyzed the production of L‐tyrosine or dihydroxyphenyl‐L‐alanine (L‐dopa) from ammonia, pyruvate, and phenol or catechol, respectively. In the production of tyrosine, an integrated equation based on an ordered ter‐uni rapid equilibrium mechanism can be used to find the kinetic parameters of TPL. In an adequately stirred system, the apparent values of‐the kinetic parameters of whole cell TPL are equal whether the cells are free or encapsulated. The apparent KM of tyrosine varies with the amount of whole cells in the system, ranging from 0.2 to 0.3 mM. The apparent KM for phenol is 0.5 mM. The apparent KM values for pyruvate and ammonia are an order of magnitude greater for whole cells than they are for the cell free enzyme. © 1995 John Wiley & Sons, Inc.
The kinetics of RCC1 inclusion body formation in Escherichia Coli
Authors: Tsai A. M. , Betenbaugh M. J. , Shiloach J.
Published: December 2004

The Regulator of Chromosome Condensation protein (RCC1) is located in both the soluble and inclusion body (IB) fractions of the whole cell lysate when expressed in Escherichia coli BL21 (pLysS) at temperatures below 30°C. When bacterial growth was carried out at 20°C, the majority of the RCC1 remained soluble up to 5.5 h postinduction, When the temperature was raised to 25°C, RCC1 IB was dominant by 1.5 h postinduction. The shift in RCC1 IB formation with temperature suggests that in addition to increased translation rates, folding and aggregation processes may contribute to RCC1 IB formation at higher temperatures. © 1995 John Wiley & Sons, Inc.
Regioselective Formation of β‐Alkyl‐α‐phenyliridabenzenes via Unsymmetrical 3‐Vinylcyclopropenes: Probing Steric and Electronic Influences by Varying the Alkyl Ring Substituent
Authors: Wu He‐Ping , Weakley Timothy J. R. , Haley Michael M.
Published: December 2004

The synthesis of unsymmetrical (Z)‐1‐alkyl‐3‐(2‐iodovinyl)‐2‐phenyl‐1‐cyclopropenes (R=Me (8 a), Et (8 b), iPr (8 c), and tBu (8 d)) and their reactions with Vaska's complex [Ir(CO)Cl(PPh3)2] and its trimethylphosphine analogue [Ir(CO)Cl(PMe3)2] were investigated. Iridabenzvalene (13/20), iridabenzene (14/21), and/or η5‐cyclopentadienyliridium complexes (15/22) were obtained in modest yields and were fully characterized by spectroscopic means. X‐ray structural data was secured for iridabenzvalene 13 d and iridabenzenes 14 a,b,d. Whereas iridabenzenes 14 a–c were stable at 75 °C for 48 h, 14 d, which possesses a bulky tBu group, rearranged cleanly to cyclopentadienyliridium 15 d at 50 °C over 15 h and displayed first‐order kinetics. The influence of the alkyl substituent on the mechanisms of iridacycle generation, isomerization, and iridabenzene regioselectivity is discussed.
Modulating Charge Transfer through CyclicD,L‐α‐Peptide Self‐Assembly
Authors: Horne W. Seth , Ashkenasy Nurit , Ghadiri M. Reza
Published: December 2004

We describe a concise, solid support‐based synthetic method for the preparation of cyclicd,l‐α‐peptides bearing 1,4,5,8‐naphthalenetetracarboxylic acid diimide (NDI) side chains. Studies of the structural and photoluminescence properties of these molecules in solution show that the hydrogen bond‐directed self‐assembly of the cyclicd,l‐α‐peptide backbone promotes intermolecular NDI excimer formation. The efficiency of NDI charge transfer in the resulting supramolecular assemblies is shown to depend on the length of the linker between the NDI and the peptide backbone, the distal NDI substituent, and the number of NDIs incorporated in a given structure. The design rationale and synthetic strategies described here should provide a basic blueprint for a series of self‐assembling cyclicd,l‐α‐peptide nanotubes with interesting optical and electronic properties.
Zur allgemeinen Definition des Wirkungsgrades
Authors: Grassmann P.
Published: December 2004

Es wird eine allgemeine Definition des Wirkungsgrades thermodynamischer Maschinen und Verfahren vorgeschlagen, beruhend auf dem Begriff der Arbeitsfähigkeit, der sich aus dem I. und II. Hauptsatz ableiten läßt. An mehreren Beispielen wird gezeigt, wie sich daraus durch Spezialisierung die Wirkungsgradbegriffe für beliebige Prozesse eindeutig ableiten lassen. Die Arbeitsfähigkeit erweist sich ferner als der gegebene Maßstab zur bildlichen Darstellung des Energieflusses in thermodynamischen Verfahren.
Grundsätzliches und Neues über die Zerstäubungstrocknung
Authors: Kirschbaum Emil
Published: December 2004

Das Aufzeigen der Merkmale im Aufbau von Zerstäubungstrocknern führt zu einer Betrachtung der Abmessungen der Teilchen, aus denen das Trockenpulver besteht. Mikroaufnahmen lassen die verschiedenen Einflüsse auf die Teilchengröße erkennen. Letztere legt ihreseits die Größe der Wärmeund Stoffaustauschzahlen fest. Das Hauptergebnis dieser theoretischen Untersuchungen ist die Trockenzeit. Je nach Teilchenabmessung schwankt sie zwischen Bruchteilen und einer Vielzahl von Sekunden. Auch der Betriebsmittelverbrauch wird untersucht; es wird gezeigt, wie der Wärmeverbrauch erniedrigt werden kann.
Schweißen hochlegierter, säure‐ und zunderfester ferritischer und austenitischer Stähle
Authors: Klosse Ernst
Published: December 2004

Für die verschiedenen Arten hochlegierter, säure‐ und zunderfester Stähle, die hauptsächlich in der chemischen Industrie verwendet werden, werden allgemein gültige Regeln über die Schweißbarkeit aufgestellt.
Über das Wesen der Technischen Überwachung
Authors: Riess Kurt
Published: December 2004

Geschichtliche Entwicklung. Verzicht des Staates zugunsten der Selbstverwaltung. Vertragsverhältnis zwischen Staat und Industrie. Gewerbe‐Aufsicht, Berufsgenossenschaft und Technische Überwachung. Das Wesen des Sicherheitsbegriffs in der Technischen Überwachung. Entwicklung seit 1938. Das Wirken auf den einzelnen Fachgebieten. Über die laufende Überwachung. Die Technische Überwachung als Glied in der Gemeinschaftsarbeit.