bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structured modeling of a microbial system: II. Experimental verification of a structured lactic acid fermentation model
Authors: Nielsen Jens , Nikolajsen Karin , Villadsen John 
Published: December 2004

AbstractA two‐compartment model for the lactic acid fermentation with Streptococcus cremoris is experimentally verified. The seven parameters of the model are determined using steady‐state chemostat data at varying values of dilution rate, D, but with a constant feed concentration, sf, of a single carbohydrate source (glucose, lactose, or galactose), and a constant feed concentration of sNf of the N source. Steady‐state measurements of the RNA content at different exit concentrations, s, of the carbohydrate are included to calculate kinetic parameters that determine the cell composition for varying operating conditions. The model is tested using data from a large set of steady‐state and non‐steady‐state experiments: batch fermentations and step and pulse experiments in a chemostat. Both qualitatively and quantitatively the major features of the model are confirmed: the external substrates enter into intracellular high‐energy building blocks, and lactic acid is formed as a by‐product of these reactions. Cell growth depends on the fraction of active components (XA) of the cell and is not accompanied by lactic acid production. Possible model modifications are discussed, primarily to obtain a better description of lactic acid fermentation at nongrowth conditions.
Modeling growth and succinoglucan production by Agrobacterium radiobacter NCIB 9042 in batch cultures
Authors: Dussap C. G. , De Vita D. , Pons A. 
Published: December 2004

AbstractWild‐type Agrobacterium radiobacter NCIB 9042 has been cultivated in batch cultures on a synthetic medium which was adapted for growth and succinoglucan production. Experiments were carried out in a 4‐L stirred‐tank aerated reactor. Glucose, biomass, polysaccharide, protein, and inorganic‐ and organic‐nitrogen concentrations were measured, and oxygen consumption and CO2 production rates were obtained by a gas‐balance technique. Nitrogen balance shows that inorganic nitrogen is entirely recovered into proteins. The carbon balance is satisfied with in ±5%. Stoichiometric equations for biomass growth and succinoglucan synthesis were established. The biosyntheticpolymer pathways including ATP and cofactor consumption were investigated. From previous studies, a (P/O) value of 1.66 is selected for oxygen sufficient cultures. The actual ATP requirements of 25.4 mmol ATP/g succinoglucan (38.5 mol ATP/mol succinoglucan), determined by a metabolic analysis, is 2.39 times the stoichiometric value. Experimental results were modeled by a system of differential equations. The exponential growth phase was described by a nitrogen‐limited Monod equation. Subsequent succinoglucan synthesis followed a slightly modified Luedeking–Piret relation partitioning internal and external polysaccharide. Experimentally determined coefficients are compared with published results for continuous culture of A. radiobacter NCIB 11883.
Protease‐catalyzed peptide synthesis using inverse substrates: The influence of reaction conditions on the trypsin acyl transfer efficiency
Authors: Schellenberger Volker , Jakubke Hans‐Dieter , Zapevalova Nina P. , Mitin Yuri V. 
Published: December 2004

AbstractBenzyloxycarbonyl‐L‐alanine p‐guanidinophenyl ester behaves as a trypsin “inverse substrate,” i.e., a cationic center is included in the leaving group instead of being in the acyl moiety. Using this substrate as an acyl donor, trypsin catalyzes the synthesis of peptide bonds that cannot be split by this enzyme. An optimal acyl transfer efficiency was achieved between pH 8 and 9 at 30°C.The addition of as much as 50% cosolvent was shown to be of minor influence on the acyl transfer efficiency, whereas the reaction velocity decreases by more than one order of magnitude. The efficiency of H‐Leu‐NH2 and H‐Val‐NH2 in deacylation is almost the same for “inverse” and normal type substrates.
Relative contributions of biological and chemical reactions to the overall rate of pyrite oxidation at temperatures between 30°C and 70°C
Authors: Boogerd F. C. , van den Beemd C. , Stoelwinder T. , Bos P. , Kuenen J. G. 
Published: December 2004

AbstractThe stoichiometry and kinetics of the spontaneous, chemical reaction between pyrite and ferric iron was studied at 30, 45, and 70°C in shake flasks at pH 1.5 by monitoring the ferrous iron, total iron, elemental sulfur, and sulfate concentration profiles in time. It was found that the sulfur moiety of pyrite was oxidized completely to sulfate. Elemental sulfur was not produced in detectable amounts. The iron moiety of pyrite was released as ferrous iron. All observed initial reaction rates could be fitted into an empirical equation. This equation includes the concentrations of ferric iron and pyrite, and a constant which is dependent on the temperature and the nature of the main anion present. It was observed that ferrous iron formed during the reaction slowed down the oxidation of pyrite by ferric iron. The extent of this effect decreased with increasing temperature. With the aid of the empirical equation, the contribution of the chemical oxidation of pyrite by ferric iron to the overall oxidation in a hypothetical plug‐flow reactor, in which biologically mediated oxdidation of pyrite and ferrous iron by oxygen also takes place, can be assessed. At 30, 45, and 70°C, respectively, 2, 8–17, and 43% of the pyrite was oxidized chemically by ferric iron. Therefore, it is expected that only in reactors operating at high temperatures with extremely thermophilic bacteria, will chemical oxidation cause a significant deviation from the apparent first order overall kinetics of biological pyrite oxidation.
NADH fluorscence in a carbon‐limited fermentation
Authors: Srivastava A. K. , Volesky B. 
Published: December 2004

AbstractThe continuous flow acetone–butanol fermentation conducted at lowered inlet feed sugar concentrations and at a constant dilution rate D =0.075 h−1 demonstrated a significant decreases in the availability of the cell population “reduction energy” (F/X), resulting in an exclusive accumulation of intermediate acids under those conditions. The cultures resumed its solvent production activity when the inlet sugar concentration in the feed stream was increased from 20 to 40 g/L at the same low growth/dilution rates. A linear correlation between the culture reduction content (F/X) and the specific butanol rate (qB) was observed under the present conditions, indicating the necessity of the NADH availability for the increased solvent production.
Recovery of bacteria from growth media by starch‐dependent floc formation
Authors: Ferenci Thomas , Lee Kin‐Sang 
Published: December 2004

AbstractAddition of starch to suspensions of Escherichia coli K‐12 resulted in the formation of bacterial flocs. The flocculation was dependent on the high expression of a receptor for starch (maltoporin) on the surface of the bacterium. Factors influencing floc formation were investigated and optimal conditions for flocculation based on cell density, starch concentration, time, and pH established. As quantitated by a sedimentation assay, over 80% of bacteria in a culture could be removed by settling without centrifugation in 3 h under optimal conditions. Floc formation was evident with bacteria containing wild‐type maltoporin but was faster and occurred to a greater extent with strains expressing a high‐affinity allele (lamB1400) of the starch receptor. Bacteria could be harvested by floc formation directly in growth medium under defined conditions of maltoporin expression and medium composition. These results demonstrate the effectiveness of starch‐dependent aggregation in the harvesting of cells, using an inexpensive, biologically acceptable agent to induce flocculation.
Effect of chemically‐induced, cloned‐gene expression on protein synthesis in E. Coli
Authors: Wood Thomas K. , Peretti Steven W. 
Published: December 2004

AbstractEarlier experiments in our lab investigated the metabolic limitations of cloned‐gene expression in bacterial cells (for over‐production of β‐lactamase). These experiments showed that the steady‐state concentration of ribosomal RNA decreased upon plasmid amplification while both the synthesis rate and steady‐state β‐lactamase mRNA level increased significantly. This appeared to indicate substantial limitation exist within the transnational machinery of the bacterial cell at high copy numbers. To establish the generality of this phenomenon, the impact increasing protein expression from pa plasmid by chemically inducing a strong promoter while maintaining constant copy number has been investigated. A plasmid has been constructed which contains the lacZ gene under control of the tac promoter and contains the parB stability locus to maintain plasmid stability. Using this vector, β‐galactosidase expression in chemostat cultures operated at specific growth rates of 0.6 h−1 was induced with IPTG such that enzyme activity was varied over a 460‐fold range. When fully induced β‐galactosidase protein production represented 14 wt % of total cell protein. As transcription was induced, the synthesis rate of the β‐galactosidase mRNA increased 42‐fold while the steady‐state level of β‐galactosidase mRNA increased only fourfold. This indicates stability may play a larger role for β‐galactosidase expression with a strong promoter than seen with β‐lactamase production in the elevated copy number system. Furthermore, rRNA synthesis rates increased at high expression rates as seen in the copy number experiments. However, unlike the amplified‐plasmid system, the steady‐state levels of rRNA increased as well. Since the total protein levels closely followed the steady‐state level of eRNA, transnational limitations are again suggested for the chemically induced transcription system.
Albumin denaturation during ultrafiltration: Effects of operating conditions and consequences on membrane fouling
Authors: Meireles Martine , Aimar Pierre , Sanchez Victor 
Published: December 2004

AbstractUltrafiltration of high‐purity grade bovine serum albumin has been carried out under various temperature between 5 and 30°C and at various cross‐flow velocities, pressures, and concentrations with the aim of studying protein denaturation and its consequences on the process. Three different pump heads have been tested. Denaturation of proteins in solution has been monitored by laser light scattering and size exclusion chromatography. The rate of protein denaturation increases with temperature, cross‐flow, and time. It is observed that membrane fouling is different whether denaturation has occurred or not. Under high‐concentration polarization, denaturation can occur in the boundary layer if the wall concentration exceeds 400 g/L. It is shown how the residence time, operating temperature, and pressure play an important part in membrane fouling. This can provide guidelines for process design and control.
Synthesis and secretion of α‐amylase by rice callus: Evidence for differential gene expression
Authors: Simmons Carl R. , Huang Ning , Cao Yicheng , Rodriguez Raymond L. 
Published: December 2004

AbstractRice seed callus expressed and secreted α‐amylase at high levels. Twenty percent of the protein secreted by the callus was αamylase. The callus secreted about 840 μg α‐amylase with 10.9 × 103 units of activity per gram dry weight callus per day. The α‐amylase from callus exhibited a more complex isoform pattern than the germinating seed α‐amylase. In addition, the level of mRNA expression by the five α‐amylase gene groups was markedly different between callus and the germinating seed. The rice callus culture has features which it attractive as a potential system for expression proteins in plant cell fermentation systems.
Gas holdup, power consumption, and oxygen absorption coefficient in a stirred‐tank fermentor under foam control
Authors: Yasukawa Masami , Onodera Masayuki , Yamagiwa Kazuaki , Ohkawa Akira 
Published: December 2004

AbstractFor a laboratory stirred‐tank fermentor (STF) with foaming system of 0.5M sulfite solution containing an anionic soft detergent, the performing of a foam‐breaking apparatus with a rotating disk (FARD)fitted to the STF was evaluated. The gas holdup in a mechanical foam‐control system (MFS), i.e., the stirred‐tank fermentor with the rotating disk foambreaker, was confirmed to be larger than that in a nonfoaming system (NS), i.e., the STF with an antifoam agent added. The agitation power in the mechanical foam control system was found to be smaller compared with the agitation power in the nonfoaming system, due to the increased gas holdup. Comparison of the oxygen absorption coefficient between the mechanical foam control system and the nonfoaming system in terms of the specific power input also demonstrated the superiority of the mechanical foam control system, not only in oxygen transfer performance but also in power input economy.
A model of interorganelle monoclonal antibody transport and secretion in mouse hybridoma cells
Authors: Bibila Theodora A. , Flickinger Michael C. 
Published: December 2004

AbstractA three compartment model (ER → Golgi → extracellular medium) is used here to describe the interorganelle transport and final secretion of an IgG2a monoclonal antibody (MAb) in 9.2.27 murine hybridoma cells. Model simulations of pulse‐chase and continuous labeling experiments are used to gain a better understanding of the kinetics of MAb interorganelle traffic. Simulation results for the continuous labeling case compare well with experimental data obtained during continuous labeling of 9.2.27 hybridoma cells. Incorporation of this compartmental transport model into our previously developed model of MAb synthesis and assembly can provide a useful tool for analyzing the dynamics and regulation of the complete antibody secretory pathway under different growth and/or nutritional conditions.
Construction of a specialized‐ribosome vector or cloned‐gene expression in E. coli
Authors: Wood Thomas K. , Peretti Steven W. 
Published: December 2004

AbstractAn expression system utilizing specialized ribosomes has been constructed with β‐galactosidase as the product. Ribosomes specific for lacZ mRNA are generated due to a mutation within the anti‐Shine‐Dalgarno region of a plasmidborne 16S rRNA gene that is complementary to a mutation within the ribosome‐binding site of lacZ. Hence, a subpopulation of ribsomes specific for translation of the cloned gene mRNA is produced. Transcription of the lacZ gene is regulated by the tac promoter, while transcription of the mutated rrnB locus is controlled by the λPL promoter. Batch experiments indicate that full induction of both operons (2 mM IPTG, 42°C) leads to maximal β‐galactosidase activity per cell at levels 35% higher than that obtained using a wild‐type ribosome expression system. Using a novel, site‐directed mutagenesis technique, construction of the specialized ribosome vector is outlined, and the results of lacZ expression are presented as transcription of both the cloned‐gene and the specialized‐ribosome locus are induced.
Continuous protein separations in a magnetically stabilized fluidized bed using nonmagnetic supports
Authors: Chetty Ashok S. , Burns Mark. A. 
Published: December 2004

AbstractContinuous protein separations were performed using a magnetically stabilized fluidized bed (MSFB) and a commercially available affinity adsorption resin that contained no magnetically susceptible material. These nonmagnetic materials can be stabilized at relatively low fields (<75 G requiring <30 W) if sufficient magnetically susceptible particles are also present in the stabilized bed. The minimum amount of magnetic particles necessary to stabilize the bed is as low as 20% by volume and is a function of various parameters including the size and density of both particles, the magnetic field strength, and the fluidization velocity. Advantages of these beds for performing separations include true continuous, countercurrent liquid‐solids contact, mass‐transfer efficiencies nearly equal to that of packed beds, and the ability of handle suspended cells or cell debris. A variety of commercially available affinity, ion‐exchange, and adsorptive supports can be used in the bed for continuous separations; results are presented for the adsorption and recovery of lysozyme from an aqueous mixture of lysozyme and myoglobin using an affinity resin.
Continuous production of Ammonium lactate by Streptococccus cremoris in a three‐stage reactor
Authors: Mulligan Catherine N. , Safi Béchara F. , Groleau Denis 
Published: December 2004

AbstractBatch and continuous fermentation studies were performed to optimize the production of ammonium lactate from whey to optimize the production of ammonium lactate from whey permeate. The product known as fermented ammoniated condensed whey permeate (FACWP) is a very promising animal feed. After an initial screening of four strains which produce predominantly L(+)‐ lactic acid, the desired isomer [D(−)‐lactic acid is toxic], Streptococcus cremoris 2487 was chosen for further study. In batch mode, pH between 6.0 and 6.5 and 35°C provided optimum incubation conditions. To stimulate a plug flow reactor, three CSTRs (continuous stirred tank reactors) were connected in tandem. For a 7.5‐h retention time, 1.6‐fold and 1.3‐fold higher productivities were obtained for three‐stage than for the single‐ and two‐stage reactors, respectively. Various retentions times were examined (5, 7.5, and 10 h; 5g/L yeast extract). Although maximum lactate productivity occurred at a 5‐h residence time (5.38 g/L H. 75% lactose utilization), lactose utilization was more complete at 7.5 h (4.38 g/L h productivity, 91% lactose utilization and a productivity, 91% lactose utilization). Retention time was increased to 15 h to obtain 95.9% lactose utilization and a productivity of 2.42g/L h for 2g/L yeast extract. Based on this lower yeast extract concentration, it was determined that ammonium lactate production and subsequent concentration by 11‐fold would yield a product (FACWP) 17% more than soybean meal (crude protein contents are equivalent, 44%) at current market prices.
Experimental simulation of dissolved oxygen fluctuations in large fermentors: Effect on Streptomyces clavuligerus
Authors: Yegneswaran P. K. , Gray M. R. , Thompson B. G. 
Published: December 2004

AbstractAn experimental Monte Carlo method was used to study the effect of fluctuations in oxygen concentration on the synthesis of antibiotics by Streptomyces clavuligerus. Air was supplied to the culture in a 2‐L fermentor in random cycles following the lognormal distribution in order to model the circulation within large production‐scale vessels. Each cycle consisted of air supply for 5 s followed by no aeration for the balance of the cycle time which ranged from 8 to 44 s, with a mean time of 20 s. Comparable experiments were also conducted with constant period cycling of air and with continuous supply of air. The yields of cephamycin C and its precursor, penicillin N, were suppressed by the Monte Carlo simulation of circulation in a large tank, as compared to constant period cycling. The concentration of dissolved oxygen remained at a low, ca. 5% of saturation, for 5–10 h longer during the Monte Carlo experiment than during the periodic aeration experiment. The biosynthetic enzymes, which are sensitive to oxygen levels, were likely affected not only by the mean time of cycling but also by the distribution of the cycles.
Biomass axial distribution in airlift bioreactor with yeast and plant cells
Authors: Assa Amir , Bar Raphael 
Published: December 2004

AbstractThis study was aimed at determining the degree of biomass homogeneity in the various parts of an internal loop airlift bioreactor, thus verifying the assumption, often made in bioreactor studies, of a well‐mixed liquid‐biomass system. Following characterization of the hydrodynamics of the vessel with water, the axial biomass distribution in the riser and downcomer was determined for plant and yeast cell suspensions of 5.8, 8.5, and 12.5 g DW/L Phaseolus vulgaris and of 30 and 46 g DW/L Saccharomyces cerevisiae. The airlift bioreactor with a surface ratio AD/AD of 1.04 and aspect ratio of 4.95 was investigated under various aeration rates. The yeast cells were found to be distributed practically uniformly throughout the vessel at the aeration rates of 0.1−1.45 vvm. However, in the case of the denser and cluster‐forming plant cells, a clear trend of a gradual bio‐mass accumulation in the downcomer, a slightly lower but uniform biomass loading in the riser, and a slightly higher biomass concentration in the gas‐liquid separator was observed at the lower aeration rates of 0.1−0.61 vvm. In the case of powderized calcium carbonate (55g/L) often used in fermentations of organic acids, a slight trend of a gradual accumulation of solids towards the bottom parts in both the downcomer and riser was observed. A better representative sampling location, in terms of solids and biomass loading, seems to be in the middle part of the vessel. It is suggested that airlift bioreactors with higher aspect ratios (>5) may be prone to a more significant inhomogeneity of solids (biomass and particles).
Rapid determination of plasmid‐carrying yeast cells by using an imaging sensor system
Authors: Endo Hideaki , Suzuki Masayasu , Sode Koji , Tamiya Eiichi , Karube Isao 
Published: December 2004

AbstractA novel imaging sensor system for the determination of plasmid carrying yeast cells was developed. The sensor system consisted of an Silicon Intensifier Target (SIT) video camera, a fluorescent microscope, and a personal computer system equipped with an image memory board. This system was based on the fact that the membrane integrity of only plasmid‐carrying cells is lost following cell growth in 5‐fluoro‐orotic acid (5‐FOA) containing medium, and consequently these target cell can be stained with fluorescent probes and detected. In this study, plasmid‐carrying cells were detected and their fraction determined in a mixture of both plasmid‐carring and plasmid‐free cells. A good correlation was observed between the values determined by this sensor system and the conventional method in the 30%‐80% range, and one assay was possible within 4 h. This sensor system could be used for the monitoring of plasmid‐carrying fraction in recombinant yeast cells during cultivation.
An expert system approach for the control of a bioprocess. I: Knowledge representation and processing
Authors: Hitzmann Bernd , Lübbert Andreas , Schügerl Karl 
Published: December 2004

AbstractFor the control of bioprocesses, a priori knowledge exists which cannot be readily incorporated as a mathematical model but which can be represented by language‐based rules, such as “IF/THEN” conditions. This knowledge is usually implemented via a process operator for the automation of the fermentation. A knowledge‐based system has been developed which can use this kind of knowledge and which is complemented by algorithmic systems, such as statistical analyses and mathematical modeling, for the supervision and control of a bioprocess. In this article, a description of this system is presented. Furthermore, the following features of the system are discussed in detail which are especially important for the development of real‐time, on‐line, knowledge‐based systems: the representation of time‐dependent knowledge; processing of imprecise, uncertain, and incomplete knowledge; the combination of shallow reasoning with model‐based reasoning; informing the bioprocess operator about the inferences and decisions; the demands of the diversity of the knowledge handling; performance; and maintenance and extension of the system.