bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of kLa by dynamic pressure method in pilot‐plant fermentor
Authors: Linek V. , Moucha T. , Doušová M. , Sinkule J. 
Published: December 2004

AbstractThe dynamic pressure method (DPM) is used for measurement of kLa in a 1‐m3 pilot scale fermentor in coalescing (distilled water) and noncoalescing (0.3 M Na2SO4 aqueous solution) batches. The method consists in recording oxygen concentration in a batch after a small pressure change (20 kPa) in the fermentor. The upward pressure change is brought about by temporary closing and subsequent throttling of outlet gas stream and the downward change by full reopening of the gas outlet. Absorption of pure oxygen yields the same kLa values as absorption of air. In noncoalescing batch, the downward kLa values are always higher than the upward values owing to spontaneous nucleation of bubbles. The experiments performed in a stirred cell confirm this behavior. Thus, only upward pressure change should be used for measurement. The correlation of kLa data measured in small (18‐L) and large (1000‐L) vessels based on power dissipated and superficial gas velocity are in a good agreement. Unlike the DPM, the classical dynamic methods yield, under the same conditions, excessively low values of kLa (the dynamic startup method) or fail to produce data at all (the dynamic method with interchange of air for N2). © 1994 John Wiley & Sons, Inc.
Transition state stabilization of subtilisins in organic media
Authors: Xu Zu‐Feng , Affleck Rhett , Wangikar Pramod , Suzawa Valerie , Dordick Jonathan S. , Clark Douglas S. 
Published: December 2004

AbstractElectrostatic forces are among the stabilizing interactions that contribute to the high degree of enzyme‐transition state complementarity. The active‐site polarity, which can differ substaintially from that of water, is thus an important determinant of transition state stabilization. Here we pose the question of whether the rate of an enzymatic reaction proceeding through a charged transition state can be increased by increasing the active‐site polarity in an organic solvent. The active‐site polarity of subtilisin has been reduced by dehydration and suspension in a nonpolar solvent (tetrahydrofuran), and then increased by adding water to the solvent. Enhancing the local polarity substantially increasing the rate of catalysis, implicating polarity as an important factor in stabilizing the charged tetrahedral transition state. Studies with subtilisins whose active sites have been modified by site‐directed mutagenesis support the role of polarity in transition state stabilization. © 1994 John Wiley & Sons, Inc.
Population dynamics of human activated natural killer cells in culture
Authors: Pierson Bryce A. , Miller Jeffrey S. , Verfaillie Catherine , McGlave Philip B. , Hu Wei‐Shou 
Published: December 2004

AbstractThe growth kinetics and population dynamics of recombinent interleukin‐2 (rlL‐2) stimulated human natural killer (NK) cell–enriched populations were studied in vitro. The NK‐enriched populations was obtained from normal peripheral blood mononuclear cells (PBMNC) by immunomagnetic bead depletion of CD3+ and CD5+ T cells. The growth kinetics of NK cells, T cells, monocytes, and total cells are shown. In the absence of PBMNC accessory cells, the NK‐enriched population showed limited expansion. In the presence of PBMNC accessory cells, the NK‐enriched population expanded threefold more than in the absence of accessory cells due to increased NK cell growth rate and increased duration of exponential growth. Using a Transwell system, which separates two cell population by a polycarbonate membrane, the accessory cells were shown to act on the NK‐enriched population via a diffusible factor. Accessory cell conditioned media was able to replace the accessory cell population to stimulate NK cell expansion. A monocyte‐enriched population prepared by sheep red blood cell rosetting of T cells was extensively phenotyped and compared with the NK‐enriched populations. Although the final cultured cells were phenotypically homogeneous for CD56+/CD3− NK cells, the initial NK precusor populations appear to be different. Namely, the NK cell precursors in the monocyte‐enriched population were predominantly CD56+/CD2−. Kinetic equations were formulated for this culture system and the effects of major culture variables are investigated.
The in vitro growth of a three‐dimensional human dermal replacement using a single‐pass perfusion system
Authors: Halberstadt Craig R. , Hardin Robert , Bezverkov Kelly , Snyder Dale , Allen Lynn , Landeen Lee 
Published: December 2004

AbstractA human dermal replacement has been developed by seeding human neonatal dermal fibroblasts onto a biosorbable polyglactin (polyglycolide/polylactide) mesh and culturing in a bioreactor. The mesh provides the proper environment for the cells to attach, grow in a three‐dimensional array, and establish a tissue matrix over a 2‐ to 3‐week culture period. The dermal replacement has been characterized and found to contain a variety of naturally occurring dermal matrix proteins, including fibronectin, glycosaminoglycans, and collagen types I and III. To efficiently and reproducibly produce this dermal tissue equivalent, a closed, single‐pass perfusion system was developed and compared with a static process. In the single‐pas perfusion system, growth medium (containing ascorbic acid) was perfused around the 4 × 6 in. pieces of mesh at specific flow rates determined by nutrient consumption and waste production rates. The flow rates used for this system indicate that a diffusion‐limited regime exists with a mean residence time greater than 1 h for essential nutrients and factors. By controlling glucose concentrations in the system to a delta of 0.70 g/L from the inlet to the outlet of the bioreactor, it took 6 fewer days to grow a tissue similar to that produced by the static system.
Stereotypic culture systems for liver and bone marrow: Evidence for the development of functional tissue in vitro and following implantation in vivo
Authors: Naughton Brian A. , Román Julia San , Sibanda Benson , Weintraub Jory P. , Kamali Vafa 
Published: December 2004

AbstractStromal cell‐associated liver cell and bone marrow (BM) culture on three‐dimensiional nylon screen or polyglycolic acid (PGA) felt templates conveys certain functional advantages to the parenchyma of these tissues. Hepatic parenchymal cells (PC) manifest long‐term (∼2 month) expression of liver‐specific activities including cytochrome P450 enzyme activity and the synthesis of albumin, fibrinogen, transferrin, and other proteins. PC also undergo proliferation in association with stromal cells that were pre‐established on these templates. PC mitoses are directly proportional to available space within the template for their expansion indication that geometric or sterotypic parameters influence the growth of these cells in vitro. BM cultured on a similar template exhibits long‐term multilineage hematopoietic expression and limited expansion of progenitor cell numbers. Progenitor cell concentration within the cultures can be substantially enhanced if these cells are liberated from co‐culture and reseeded onto a template containing fresh stromal cells. BM and liver cel cultures established on felt composed of bioresorbable PGA filaments was grafted into various sites in rats. Liver co‐cultures generated sinusoids and other liver‐like structures in situ; active hematopoietic blasts were observed at sites of BM co‐culture grafts. Biodegradable polymer constructs may prove useful for certain clinical applications as vehicles for the delivery of tissues that were engineered in culture.
Effects of biofilm structures on oxygen distribution and mass transport
Authors: de Beer Dirk , Stoodley Paul , Roe Frank , Lewandowski Zbigniew 
Published: December 2004

AbstractAerobic biofilms were found to have a complex structure consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. The oxygen distribution was strongly correlated with these strutures. The voids facilitated oxygen transport from the bulk liquid through the biofilm, supplying approximately 50% of the total oxygen consumed by the cells. The mass transport rate from the bulk liquid is influenced by the biofilm structure; the observed exchange surface of the biofilm is twice that calculated for a simple planar geometry. The oxygen diffusion occurred in the direction normal to the cluster surfaces, the horizontal and vertical components of the oxygen gradients were of equal importance. Consequently, for calculations of mass transfer rates a three‐dimensional model is necessary. These findings imply that to accurately describe biofilm activity, the relation between the arrangement of structural components and mass transfer must be undrstood. © 1994 John Wiley & Sons, Inc.
Phase fluorometric sterilizable optical oxygen sensor
Authors: Bambot Shabbir B. , Holavanahali Raja , Lakowicz Joseph R. , Carter Gary M. , Rao Govind 
Published: December 2004

AbstractWe report here on a low‐cost, optical oxygen sensor as an attractive alternative to the widely used amperometric Clark‐type oxygen electrode for measuring dissolved oxygen tensions in cell cultures and bioreactor. Our sensor is based on the defferential quenching of the fluorescence lifetime of chromophore in response to the partial pressure of oxygen. This is measured as a phase shift in fluorescence emission from the chromophore due to oxygen quenching when excited by an intensity modulated beam of light. In this article we demonstrate the advantages of lifetime‐based optical methods over both intensity based optical methods and amperometric electrodes. Our sensor is particularly suitable for measuring dissolved oxygen in bioreactors. It is autoclavable, is free of maintenance requirements, and solvents the problems of long‐term stability, calibration drifts, and reliable measurement of low oxygen tensions in dense microbial cultures that limit the utility of Clark‐type elcectordes. © 1994 John Wiley & Sons, Inc.
Co‐immobilized Nitrosomonas europaea and Nitrobacter agilis cells: validation of a dynamic model for simultaneous substrate conversion and growth in κ‐carrageenan gel beads
Authors: Hunik Jan H. , Bos Cees G. , van den Hoogen Marijke P. , De Gooijer Cornelius D. , Tramper Johannes 
Published: December 2004

AbstractA dynamic model for two microbial species immobilized in a gel matrix is presented and validated with experiments. The model characterizes the nitrification of ammonia with Nitrosomonas europaea and Nitrobacter agilis co‐immobilized in K‐carrageenan gel beads. The model consists of kinetic equations for the microorganisms and mass transfer equations for the substrates and products inside and outside the gel beads. The model predicts reactor bulk concentrations together with the substrate consumption rate, product formation, and biomass growth inside the gel beads as a function of time. A 50–day experiment with immobilized cells in a 3.3‐dm3 air‐lift loop reactor was carried out to validate the model. The parameter values for the model were obtained from literature and separate experiments. The experimentally determined reactor bulk concentrations and the biomass distribution of the two microorganisms in the gel beads were well predicted by the model. A sensitivity analysis of the model for the given initial values indicated the most relevant parameters to be the maximum specific growth rate of the microorganisms, the diffusion coefficient of oxygen, and the radius of the beads. The dynamic model provides a useful tool for further study and possible control of the nitrification process. © 1994 John Wiley & Sons, Inc.
Production of lignin peroxidase by Phanerochaete chrysosporium immobilized on porous poly(styrene‐divinylbenzene) carrier and its application to the degrading of 2‐chlorophenol
Authors: Ruckenstein Eli , Wang Xiao‐Bai 
Published: December 2004

AbstractPorous poly(styrene‐divinylbenzene) carriers, for the immobilization of white rot fungus Phanerochaete chrysosporium have been prepared by the concentrated emulsion polymerization method. The concentrated emulsion consists of a mixture of styrene and divinylbenzene containing a suitable surfactant and an initiator as the continuous phase, and water as the dispersed phase. The polymerization of the monomers of the continuous phase generated the polymer carrier with a porcus structure. The white rot fungus Phanerochaete chrysosporium has been immobilized on porous poly(styrene–divinylbenzene) carriers and used for the batch production and the repeated batch production of lignin peroxidase in shake cultures based on a carbon‐limited medium containing veratryl alcohol. The best results were achieved when a spore inoculum was used for immobilization instead of 1‐day‐old mycelial pellets, for both the batch production and the repeated batch production. The porous poly(styrene–divinylbenzene) immobilized Phanerochaete chrysosporium and freely suspended mycelial pellets were used as biocatalysts for the degradation of 2‐chilorophenol in a 2‐L bioreactor. The porous poly(styrene‐divinylbenzene) particle (diameter ≅ 0.2 cm) immobilized spores exhibited a much higher activity in the degradation of 2‐chlorophenol than the freely suspended mycelial pellets. © 1994 John Wiley & Sons, Inc.
Modeling approach to control of carbohydrate metabolism during citric acid accumulation by Aspergillus niger: II. Sensitivity analysis
Authors: Torres Néstor V. 
Published: December 2004

AbstractSteady state sensitivity analysis of a model of carbohydrate metabolism and anaplerotic synthesis of oxalacetate were, in Aspergillus niger under conditions of citric acid accumulation, carried out. The flux and metabolite concentration control structure of the system obtained shows that the hexokinase/substrate transport step is the main controlling step of the pathway. The quantitative contribution of the other enzyme catalyzed or transport steps are also discussed. These results allow the design of a proper strategy of biotechnological manipulation aimed at improvement of the process. © 1994 John Wiley & Sons, Inc.
Overproduction of glycogen in Escherichia coli blocked in the acetate pathway improves cell growth
Authors: Dedhia Neiley N. , Hottiger Thomas , Bailey James E. 
Published: December 2004

AbstractExcessive production of acetate is a problem frequently encountered in aerobic high‐cell‐density fermentations of Escherichia coli. Here, we have examined genetic alterations resulting in glycogen overproduction as a possible means to direct the flux of carbon away from the acetate pool. Glycogen overaccumulation was achieved either by using a regulatory glgQ mutation or by transforming cells with a plasmid containing the glycogen biosynthesis genes glgC (encoding ADPG pyrophosphorylase) and glgA (encoding glycogen synthase) under their native promoter. Both strategies resulted in an approximately five‐fold increase in glycogen levels but had no significant effect on acetate excretion. The glgC and glgA genes were then placed under the control of the isopropyl‐‐‐D‐thiogalactopyranoside (IPTG) inducible tac promoter, and this construct was used to stimulate glycogen production in a mutant defective in acetate biosynthesis due to deletion of the ack (acetate kinase) and pta (phosphotransacetylase) genes. If glycogen overproduction in the ack pta strain was induced during the late log phase, biomass production increased by 15 to 20% relative to uninduced controls. Glycogen overaccumulation had a significant influence on carbon partitioning: The output of carbon dioxide peaked earlier than in the control strain, and the levels of an unusual fermentation byproduct, pyruvate, were reduced. Exogenous pyruvate was metabolized more rapidly, suggesting higher activity of gluconeogenesis or the tricarboxylic acid (TCA) cycle as a result of glycogen overproduction. Potential mechanisms of the observed metabolic alterations are discussed. Our results suggest that ack pta mutants over producing glycogen may be a suitable starting point for constructing E. coli strains with improved characteristics in high‐cell‐density fermentations. © 1994 John Wiley & Sons, Inc.
Interactions of microbial biofilms with toxic trace metals: 1. Observation and modeling of cell growth, attachment, and production of extracellular polymer
Authors: Hsieh Ke Ming , Murgel George A. , Lion Leonard W. , Shuler Michael L. 
Published: December 2004

AbstractAdsorbent surfaces in natural and engineered systems are frequently modifies by bacterial attachment, growth of a biofilm, and bacterial production of extracellular polymer. Attached cells or sorbed polymers may alter the metal‐binding characteristics of the supporting substratum and influence metal partitioning. The interdependent behavior of toxic trace metal partitioning and biofilm development requires description of the interaction between cell growth with its accompanying polymer production and metal speciation. In this article, the first of a two part series, a mechanistic model is developed to describe the growth of a film‐forming bacterium which adheres to a substratum through the production of extracellular biopolymers. Each bacterial cell was modeled as a two‐component structure consisting of active cell mass and biopolymer. The biopolymer component was further divided into cell‐associated and dissolved categories to distinguish which remained naturally bound to cell surfaces from that which did not. Use of this structured model permitted independent description of the dynamics of cell growth, and polymer production, both of which may influence trace metal behavior. Employing parameters obtained from independent experiments as well as published values, the model satisfactorily predicts experimental observations of bacterial growth, attachment and detachment, biopolymer production, and adsorption of polymer onto solid (glass) surfaces. The model stimulated transient and steady‐state biofilm systems equally well. In the second article in this series, we describe how this model may be extended and utilized to make predictions of the behavior of transient and steady‐state biofilm systems in the presence of a toxic transition metal(Pb). © 1994 John Wiley & Sons, Inc.
Saccharification and fermentation of Sugar Cane bagasse by Klebsiella oxytoca P2 containing chromosomally integrated genes encoding the Zymomonas mobilis ethanol pathway
Authors: Doran Joy B. , Aldrich H. C. , Ingram L. O. 
Published: December 2004

AbstractPretreatment of sugar cane bagasse is essential for a simultaneous saccharification and fermentation (SSF) process which uses recombinant Klebsiella oxytoca strain P2 and Genencor Spezyme CE. Strain P2 has been genetically engineered to express Zymomonas mobilis genes encoding the ethanol pathway and retains the native ability to transport and metabolize cellobiose (minimizing the need for extracellular cellobiase). In SSF studies with this organism, both the rate of ethanol production and ethanol yield were limited by saccharification at 10 and 20 filter papaer units (FPU) g−1 acid‐treated bagasse. Dilute slurries of biomass were converted to ethanol more efficiently (over 72% of theoretical yield) in simple batch fermentations than slurries containing high solids albeit with the production of lower levels of ethanol. With high solids (i.e., 160 g acid‐treated bagasse L−1), a combination of 20 FPU cellulase g−1 bagasse, preincubation under saccharification conditions, and additional grinding (to reduce particle size) were required to produce ca. 40 g ethanol L−1. Alternatively, almost 40 g ethanol L−1 was produced with 10 FPU cellulase g−1 bagasse by incorporating a second saccharification step (no further enzyme addition) followed by a second inoculation and short fermentation. In this way, a theoretical ethanol yield of over 70% was achieved with the production of 20 g ethanol 800 FPU−1 of commercial cellulase. © 1994 John Wiley & Sons, Inc.
Biodegradation process development using a bacterial cytochrome in vivo
Authors: Horowitz Jeffrey B. , Vilker Vincent L. 
Published: December 2004

AbstractPseudomonas putida PpG786 that contains the inducible enzyme system cytochrome P‐450cam is considered for use as specialized biomass fore detoxification of hazardous hydrocarbons. The test substrate 1,2‐dibromochloropropane (DBCP) is used to assess the organohalide degradation activity of P. Putida PpG786. Activity was found to be a strong function of intracellular heme content, variables which affect the culturing and processing of the cells, and oxygen tension in the degradation incubation medium. The lifetime for maintaing active biomass in chemostat washout operation, after including substrate was removed and then restarted, was also studied. These results indicate that initial activity of the P. Putida biomass is high enough, and decays slowly enough, so that industrial wastewater treatment at the operating conditions of a sequencing batch reactor (SBR) could remove hazardous compounds. © 1994 John Wiley & Sons, Inc.
Cyclic AMP regulation of tylosin biosynthesis and secondary metabolism in Streptomyces fradiae
Authors: Tata Murthy , Menawat Anil S. 
Published: December 2004

AbstractAdenosine 3′:5′ cyclic monophosphate seems to regulate antibiotic biosynthesis and secondary metabolism in tylosin‐producing cultures of Streptomyces fradiae C373.1. A dose‐dependent response is observed by exogenous additions of dibutyryl cyclic AMP (cAMP), and is related to the nutritional status of the culture. Addition of cAMP to cultures growing in nutritionally lean media caused higher cumulative antibiotic tigers and some cellular differentiation compared with the control. In nutritionally rich media, a qualitatively different behavior resulted: an almost instantaneous shift toward secondary metabolism occurred. The response is characterized by extensive cellular differentiation with little growth and only a trace of antibiotic production. The possible role of cyclic AMP n the regulation of tylosin biosynthesis and secondary metabolism and its relation to specific nutrient limitations in synthetic, defined media in Streptomyces fradiae is discussed. © 1994 John Wiley & Sons, Inc.
A new method for studying microaerobic fermentations. I. A theoretical analysis of oxygen programmed fermentation
Authors: Lidén Gunnar , Frazén Carl Johan , Niklasson Claes 
Published: December 2004

AbstractAn experimental method for studying microaerobic fermentation, called oxygen programmed fermentation, is introduced. The method if based on a chemostat. The mathematical equations governing the dynamics of the system are derived and simulations are made for two principally different cases: a purely respirative organism, and an organism capable of fermentation during oxygen limitation. It is shown that at a suitably chosen ramp rate, the dissolved oxygen concentration in the broth can be made to decrease almost linearly. It is suggested that the greatest use of oxygen programmed fermentation will be in initial experiments. Compared with chemostat studies, a scan of different oxygenation rates will provide a time‐saving method of finding the interacting regions for metabolic transitions. Furthermore it is shown that the methods makes it possible to study cell physiology at condition which would normally lead to washout. © 1994 John Wiley & Sons, Inc.