bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuous ethanol production by immobilized yeast reactor coupled with membrane pervaporation unit
Authors: Shabtai Y. , Chaimovitz S. , Freeman A. , Katchalski‐Katzir E. , Linder C. , Nemas M. , Perry M. , Kedem O. 
Published: December 2004

AbstractA system comprised of an immobilized yeast reactor producing ethanol, with a membrane pervaporation module for continuously removing and concentrating the produced ethanol, was developed. The combined system consisted of two integrated circulation loops: In one the sugar‐containing medium is circulated through the membrane pervaporation module. The two loops were interconnected in a way allowing for separate parameter optimization (e.g., flow rate, temperature, pH) for each loop.The fermentation unit was 2.0 L bioreactor with five equal segments, packed with 5‐mm beads of immobilized yeasts. The bead matrix was a crosslinked polyacrylamide hydrazide gel coated with calcium alginate. The fast circulation loop of the bioreactor allowed for efficient liberation of CO2 at the top of the immobilized yeast reactor. Continuous operation of the uncoupled reactor for over 50 days with inflowing defined medium or dilute molasses at a residence time of 1.25 h yielded ethanol at a rate of about 10 g/L h.The pervaporation unit was constructed from four 60‐cm‐long tubular membranes of silicone composite on a polysulfone support. The output from the fermentor was circulated through the inside of the tubes of a unit with a total surface area of 800 cm2, having an average flux of 150 mL/h, and selectivities to ethanol vs. water up to 7. A vacuum of 30 mb was applied to the outside of the tubes, removing 20–30 g of ethanol per hour, which was collected in condensors. The continuous removal of ethanol, avoiding inhibition of the fermentation process, resulted in an improved productivity and allowed the use of high sugar concentrations (40% wt/vol) offering the potential of a compact system with reduced stillage.The combined system of ethanol production and removal enabled an operative steady state at which the liquid volume of the system, and the concentrations of ethanol within the reactor (˜4% wt/vol), as well as within the flux crossing the pervaporation membrane (17%–20% wt/vol) were kept constant. At the steady state, a 40% wt/vol sugar solution could be continuously added to the fermentor when 12%–20% wt/vol clear ethanol solution was continuously removed by the pervaporation unit. Membrane fouling was reversed by short washing steps, and continuous step operation was maintained by working with two different modules that were interchanged. In this manner, long term continuous operation (over 40 days) was achieved with a productivity of 20–30 g/L h, representing over a twofold increase relative to the continuously operated reactor uncoupled from the membrane and a fivefold increase in comparison with the value obtained fro a corresponding batch fermentation.
Kinetic analysis of cephalosporin biosynthesis in Streptomyces clavuligerus
Authors: Malmberg Li‐Hong , Hu Wei‐Shou 
Published: December 2004

AbstractA kinetic model describing the cephalosporin biosynthesis in Streptomyces clavuligerus was developed. Using previously reported kinetic data of biosynthetic enzymes, we examined the kinetics of cephalosporin production. The predicted time profile of the specific production rate during a batch culture parallels that of experimental observation. Sensitivity analysis reveals that δ‐(L‐α‐aminoadipyl)‐L‐cysteinyl‐D‐valine (ACV) synthetase is the rate‐limiting enzyme. The effect of amplifying ACV synthetase on the specific production rate was analyzed theoretically. Increasing ACV synthetase enhances the production rate initially until ACV synthetase enhances the production rate initially until deacetocycephalosporin C hydroxylase becomes rate‐limiting. Such kinetic analysis can provide a rational basis for modifying the biosynthetic machinery of cephalosporin through gene cloning.
Diffusion of lactose in k‐carrageenan/locust bean gum gel beads with or without entrapped growing lactic acid bacteria
Authors: Arnaud J. P. , Lacroix C. 
Published: December 2004

AbstractEffective diffusion coefficients (De) of lactose in κ‐carrageenan (2.75% wt/wt)/locust bean gum (0.25% wt/wt) (LBG) gel beads (1.5–2.0‐mm diameter)with or without entrapped lactic acid bacteria (LAB) were determined at 40°C. The effects of lactose concentration, bacteria strain (Streptococcus salivarius subsp. thermophilus and Lactobacillus casei subsp. casei) and cell content at various steps of the fermentation process (after immobilization, pre‐incubation of the beads and successive fermentations) were measured on De as a first step for process modelling. Results were obtained from transiend concentration changes n well‐stirred lactose solutions in which the beads were suspended. A mathematical model of unsteady‐state diffusion in a sphere was used, and De was obtained from the best fit of the experimental data. Diffusivity of lactose in cell‐tree beads was significantly lower than in pure water mainly because of the obstruction effect of the polymer chains and the hydration region. Furthermore, effective diffusivity and equilibrium partition factor were independent of lactose concentration in the range from 12.5 to 50 g/L. No significant difference was found for De (effective diffusivity) and Kp (partition) coefficients between beads entrapping S. thermophilus (approximately 5 × 109 CFU/mL) and cell‐free beads. On the other hand higher cell counts obtained with L. casei (close to 1.8 × 1011 CFU/mL) increased mass transfer resistance resulting in lower effective diffusivities and Kp. Finally, the effects of the type of bacteria and their distribution in the beads on the diffusivity were also discussed.
Design and evaluation of a two‐stage, cyclic, recombinant fermentation process
Authors: Curless C. , Fu K. , Swank R. , Menjares A. , Fieschko J. , Tsai L. 
Published: December 2004

AbstractA two‐stage, cyclic fed‐batch fermentation process to produce recombinant human lymphokine was designed. The organism used in the study was Escherichia coli K‐12 containing a temperature‐sensitive walkaway plasmid bearing an insert which codes for a human lymphokine. Transcription of the recombinant gene is controlled by a lambda repressor/pL promoter system. The lambda promoter is regulated by the temperature‐sensitive product of the cl857 gene at 30°C, but at 42°C the promoter is derepressed. The first or growth, stage of the process was maintained at 28°C and operated in the fed‐batch mode. The vessel was fed at a rate which gives a constant specific growth rate using a media designed to maintain a constant optical density OD600 of 50. After the volume in the first stage reached the maximum working volume of the vessel (12 L), a portion of the vessel contents was transferred to the second stage. The second, or induction/product formation, stage also operated in the fed‐batch mode, was kept at 42°C, and was fed with a media that is conducive to recombinant human lymphokine synthesis. An optical density of more than 100 was consistently achieved in the second stage. Thirty cycles were completed with a consistent yield of human lymphokine and cell density in each cycle. The process was used to produce 200 L of OD600 50 material from the first stage in 10 days. The volumetric productivity (g lymphokine/L. day) of the two‐stage, cyclic fed‐batch process is twice that of a single‐stage, fed‐batch fermentation process.
Catalytic action of L‐2‐halo acid dehalogenase on long‐chain L‐2‐haloalkanoic acids in organic solvents
Authors: Hasan A. K. M. Quamrul , Takada Harumi , Esaki Nobuyoshi , Soda Kenji 
Published: December 2004

AbstractA Lyophilized preparation of L‐2‐halo acid dehalogenase was not only stable but also catalytically active in anhydrous dimethyl sulfoxide, toluene, and other organic solvents. 2‐Halo acids with long alkyl (C5‐C16) or aromatic (phenyl and benzyl) side chains were inert in water but dehalogenated effectively in anhydrous dimethyl sulfoxide by the lyophilized enzyme. Long chain 2‐haloalkanoic acids such as 2‐bromohexadecanoic acids were better as substrate than short‐chain halo acids (e.g., 2‐chloropropanoic acid). The dehalogenation proceed with inversion of C2 configuration to produce the corresponding (2R)‐2‐hydroxy acids in anhydrous dimethyl sulfoxide in the same way as found in water.
Product enhancement and recovery from transformed root cultures of Nicotiana glauca
Authors: Green K. D. , Thomas N. H. , Callow J. A. 
Published: December 2004

AbstractTransformed roots of Nicotiana glauce synthesize the alkaloids nicotine and anabasine at levels reflecting the parent plants. Media composition, strength, and pH were evaluated with respect to biomass yield and productivity. Full‐strength Gamborg's B5 medium proved the best for biomass yield while half‐strength, or low‐salt, medium enhanced alkaloid accumulation. A detailed investigation of media nitrate levels demonstrated how these may be manipulated to promote growth and intracellular or extracellular alkaloid levels. High nitrate concentrations were found to significantly enhance media alkaloid levels at the end of the growth phase. Media pH is also important, although transformed roots will grow in Gamborg's B5 medium between pH 3 and 9, root biomass is favored by an increase in medium alkalinity, while alkaloid release is encouraged by mildly acidic pH.Transformed roots release a proportion of their secondary metabolites into the growth medium. By continually removing root products, any feedback inhibition on enzymatic reactions is reduced, as are the toxic effects resulting from product accumulation. In this article we describe the use of Amberlite resins (XAD‐2 and XAD‐4) to enhance alkaloid levels (nicotine and anabasine) of hairy root cultures of Nicotiana glauca by a factor of 10 with no adverse effect on root growth. The performance of the Amberlite columns was subsequently investigated with respect to alkaloid adsorption and desorption, including an evaluation of the effects of pH and loading capacity. The resins also adsorb media constituents which are identified and quantified as part of this work. Resulting nutritional stresses are thought to be partly responsible for enhancing secondary metabolism at the expense of biomass yield. However, the net effects of using Amberlite resins as a means of product removal significantly increases the overall product yield and the extent to which products are released into the growth medium.
Measurement of the change in aerosol size distribution with bacterial growth in a pilot scale fermentor
Authors: Szewczyk Krzysztof W. , Lehtimäki Matti , Pan Man‐Juan , Krishnan Usha , Willeke Klaus , Elliott Diane D. , Muth William L. 
Published: December 2004

AbstractA number of industrial processes require the addition of materials to the fermentation broth that are hazardous to health and environment. Agitation of broths inoculated with microorganisms can potentially release aerosols large enough to carry the microorganisms. The influence of agitation, air flow, and bacterial growth on aerosol size distribution, air flow, and bacterial growth on aerosol size distribution was investigated in an industrial pilot scale fermentor. A decrease in particle concentration was observed with increase in bacterial growth; this change was more pronounced in the size range above 2 μm. The aerosol size distribution was found to be practically independent of air flow rate and agitation rate for sizes less than 2 μm. However, for particles largar than 2 μm, the concentration was found to increase with an increase in air flow rate and agitation rate.
Design and evalution of control strategies for high cell density fermentations
Authors: O'Connor Gregory M. , Sanchez‐Riera Fernando , Cooney Charles L. 
Published: December 2004

AbstractA methodology for the design and evalution of bioprocess control strategies is presented. The strategies manage nutrient supply with demand and vary with the metabolic condition and phase of fermentation operation. Six carbon source addition strategies are based on different combinations of available measurements; they are described and evaluated under different operating conditions for yeast cultivation. It is concluded that a single control strategy is not the most appropriate under all possible operating conditions. An oxygen uptake rate‐based control strategy performs better with a mean respiratory quotient (RQ) value less than 1.1 during an oxygen limitation than an ethanol control strategy which had a mean RQ of 14. The designed strategies and an approach of applying the strategy that best matches fermentation conditions consistently enables achievement of high cell densities 78.7 g DCW/L and yields 0.50 g DCW/g glucose as the mean values for three fermentations.
Reductive biotransformation by wild type and mutant strains of Saccharomyces cerevisiae in aqueous‐organic solvent biphasic systems
Authors: Nikolova P. , Ward O. P. 
Published: December 2004

AbstractWhole cells of Saccharomyces cerevisiae analyzed the conversion of benzaldehyde to benzyl alcohol in aqueous‐organic biphasic media. Reaction rate increased dramatically as moisture content of the solvent was increased in the range 0% to 2%. The highest biotransformation rates were observed when hexane was used as organic solvent. Benzaldehyde was also converted to benzyl alcohol by a cell‐free crude extract in biphasic systems containing hexane, although the rate of product formation was much lower. Mutant strains of S. cerevisiae lacking some or all of the ADH isoenzymes, ADH I, II, and III, manifested similar rates for bioconversion of benzaldehyde to benzyl alcohol in both aqueous and two‐phase systems. In general, conversion rates observed in aqueous media were 2 to 3 times higher than those observed in hexane containing 2% moisture.
Development and experimental evaluation of a steady‐state, multispecies biofilm model
Authors: Rittmann Bruce E. , Manem Jacques A. 
Published: December 2004

AbstractA steady‐state model for quantifying the space competition in multispecies biofilms is developed. The model includes multiple active species, inert biomass, substrate utilization and diffusion within the biofilm, external mass transport, and detachment phenomena. It predicts the steady‐state values of biofilm thickness, species distribution, and substrate fluxes. An experimental evaluation is carried out in completely mixed biofilm reactors in which slow‐growing nitrifying bacteria compete with acetate‐utilizing heterotrophs. The experimental results show that the model successfully describes the space competition. In particular, increasing acetate concentrations causes NH4+‐N fluxes to decrease, because nitrifiers are forced deeper into the biofilm, where they experience greater mass‐transport resistance.
Polyoxazoline‐Peptide adducts that retain antibody avidity
Authors: Velander William H. , Madurawe Rapti D. , Subramanian Anuradha , Kumar Guneet , Sinai‐Zingde Gurudas , Riffle Judy S. , Orthner Carolyn L. 
Published: December 2004

AbstractSynthetic polymers have long been used to modify various properties of proteins such as activity and solubility. Polyethylene glycol (PEG) has been widely used to form adducts with enzymes and antibodies. In this study, the polyoxazoline family of water‐soluble polymers was used to synthesize adducts containing a synthetic peptide recognized by a monoclonal antibody (MAb) directed against human protein C (hPC). This is the first application of direct conjugation of unterminated or “living” polymer to a peptide. The avidity of the antibody for the various adducts was characterized with respect to size and hydrophilicity of methyl‐ and ethyl‐substituted polyoxazoline polymers (POX). Avidity of the adducts was not found to be dependent upon the hydrophilicity and was slightly decreased due to polymer modification. The methyl‐POX‐peptide adducts were found to be highly water soluble, while the ethyl‐POX‐peptide adducts showed sporadic problems with aqueous solubility. Because the polymer‐peptide adducts retained avidity for the antibody, polyoxazoline polymers may have potential application to protein‐adduct chemistry.
Factors affecting 2‐hydroxypropiophenone formation by benzoylformate decarboxylase from Pseudomonas putida
Authors: Wilcocks R. , Ward O. P. 
Published: December 2004

AbstractBenzoylformate (100 mM) was quantitatively converted to the acyloin compound, 2‐hydroxypropiophenone (61.76 mM) and benzaldehyde (38.2 mM) by an enzyme extract from Pseudomonas putida ATCC 12633 in the presence of 1.6M acetaldehyde. Biotransformations were carried out at pH 6.0 and 30°C with an incubation time of 60 min. Activity of the acyloin forming enzyme, benzoylformate decarboxylase, was 1.23 units/mL in the biotransformation mixture. Acyloin formation increased dramatically with pH in the range 4–5 and had a broad activity plateau in the pH range 5–8. A broad temperature optimum for acyloin formation was also observed in the range 20–40°C.
Biocatalytic synthesis of acrylates in organic solvents and supercritical fluids: I. Optimization of enzyme environment
Authors: Kamat Sanjay , Barrera Juliet , Beckman J. , Russell Alan J. 
Published: December 2004

AbstractBiocatalytic transesterification of methylmethacrylate is possible in many different solvents. The reaction rate is readily controlled by variation in solvent physical properties. The reaction proceeds better in hydrophobic solvents, and activity can be restored in hydrophilic solvents by the addition of water. We have now demonstrated that supercritical carbon dioxide is not a good solvent for the reaction between 2‐ethlhexanol and methylmethacrylate. It apperars that the supercritical carbon dioxide may either alter the pH of the microaqueous environment associated with the protein or reversibly form covalent complexes with free amine groups on the surface of the enzyme. Although supercritical carbon dioxide is a poor solvent for acrylate transesterification, many other supercritical fluids (ethane, ethylene, sulfur hexafluoride, and fluoroform) are better than most conventional solvents. In supercritical ethane it is possible to control the activity of the enzyme by changing pressure, and the enzyme appears to follow Michaelis–Menten Kinetics. We find that sulfur hexafluoride, the first anhydrous inorganic solvent in which biocatalytic activity has been reported, is a better solvent than any conventional or supercritical organic fluid tested.
Chemostat cultivation of Candida blankii on sugar cane bagasse hemicellulose hydrolysate
Authors: Meyer P. S. , Du Preez J. C. , Kilian S. G. 
Published: December 2004

AbstractA Candida blankii yeast isolate was grown in sugar cane bagasse hemicellulose hydrolysate at 38°C in carbon‐limited chemostat culture. The pretreatment of the acid hydrolysate prior to microbial cultivation consisted of partial neutralization with ammonia and sodium hydroxide, plus the addition of phosphorus, which was the only other growth‐limiting nutrient apart from nitrogen. The cell yield coefficient on nitrogen was 16.78. The critical dilution rate was higher (0.35 h−1) in diluted hydrolysate than in undiluted hydrolysate (0.21 h−1). In undiluted hydrolysate at a dilution rate of 0.1 h−1 and pH 4, where aseptic procedures proved unnecessary, the cell and protein yield coefficients were 0.53 and 0.26, respectively, and no residual carbon substrates (D‐xylose, L‐arabinose, D‐glucose, and acetic acid) were detected. The cell yield on oxygen increased linearly as a function of dilution rate. The cellular content of protein, carbohydrate, and RNA also increased with an increase in dilution rate, whereas the DNA content decreased slightly. C. blankii has considerable potential for the production of single cell protein from hemicellulose hydrolysate, because of its ability to utilize all of the major carbon substrates in the hydrolysate at a low pH and at a relatively high temperature with a high protein yield. © 1992 John Wiley & Sons, Inc.
The use of laminar tube flow in the study of hydrodynamic and chemical influences on polymer flocculation of Escherichia coli
Authors: Whittington P. N. , George N. 
Published: December 2004

AbstractThe optimization of microbial flocculation for subsequent biomass separation must relate the floc properties to separation process criteria. The effects of flocculant type, dose, and hydrodynamic conditions on floc formation in laminar tube flow were determined for an Escherichia coli system. Combined with an on‐line aggregation sensor, this technique allows the flocculation process to be rapidly optimized. This is important, because interbatch variation in fermentation broth has consequences for flocculation control and subsequent downstream processing. Changing tube diameter and length while maintaining a constant flow rate allowed independent study of the effects of shear and time on the flocculation rate and floc characteristics. Tube flow at higher shear rates increased the rate and completeness of flocculation, but reduced the maximum floc size attained. The mechanism for this size limitation does not appear to be fracture or erosion of existing flocs. Rearrangement of particles within the flocs appears to be most likely. The Camp number predicted the extent of flocculation obtained in terms of the reduction in primary particle number, but not in terms of floc size. © 1992 John Wiley & Sons, Inc.
Structure and sucrose hydrolysis activity of Saccharomyces cerevisiae aggregates
Authors: Fontana Angélique , Bore Christian , Ghommidh Charles , Guiraud Joseph P. 
Published: December 2004

AbstractThe sucrose hydrolysis activity of dense spherical yeast flocs, cultivated on a sucrose medium in a continuous reactor with internal settler, is nearly proportional to the particle surface. From computer simulation, in good agreement with experimental determinations, the calculated sucrose penetration depth is in the range 0.2–0.3 mm, a dimension smaller than the usual diameter of strongly flocculating yeast particles. From specific gravity determinations, the flocs can be considered as homogeneous and cannot exhibit a fractal structure, reported in the literature for a number of microbial aggregates. However, the analysis of the sucrose hydrolysis rates reveals that the cell density may be lower in the outer layer of the flocs. © 1992 John Wiley & Sons, Inc.
CHO cell responses to low oxygen: Regulation of oxygen consumption and sensitization to oxidative stress
Authors: Lin Andy A. , Miller William M. 
Published: December 2004

AbstractWe have investigated the regulation of oxygen consumption and modulation of glutathione levels in CHO‐K1 cells under oxygen‐limiting conditions. We report here suppression of oxygen consumption and alteration of the supply‐dependent relationship as a consequence of prolonged hypoxic or anoxic exposure. The suppression is characterized by an increase in the value of P (the oxygen tension at which oxygen consumption is half maximal). Under prolonged anoxia there is also a decrease in the cells' potential to use oxygen. Elevated glucose consumption under low oxygen conditions may contribute to the suppression in respiration. The glutathione concentration remains constant throughout hypoxic exposure but may decrease by as much as 40% under anoxia. The glutathione level in hypoxic and anoxic cells increases by two‐ and four‐fold, respectively, over that of the control cells when exposed to a cytotoxic level of oxygen (93%). This suggests that anoxic and hypoxic exposure sensitizes CHO cells to oxidative stress. © 1992 John Wiley & Sons, Inc.