bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics, equilibria, and modeling of the formation of oligosaccharides from D‐glucose with Aspergillus niger glucoamylases I and II
Authors: Nikolov Zivko L. , Meagher Michael M. , Reilly Peter J. 
Published: May 2005

AbstractNear‐homogeneous forms of glucoamylases I and II, previously purified from an industrial Aspergillus niger preparation, were incubated with D‐glucose at a number of temperatures and pH values. Kinetics and equilibria of the formation of α,β‐trehalose, kojibiose, nigerose, maltose, isomaltose, panose, and isomaltotriose, which with isomaltotetraose were the only products formed, were determined. There was no difference in the abilities of GA I and GA II to form these products. Activation energies for the formation of maltose and panose were lower than those of the other Oligosaccharides. Relative rates of oligosaccharide production based on glucoamylase hydrolytic activity did not vary significantly between pH 3.5 and 4.5 but were lower at pH 5.5. Maltose was formed much faster than any other product. Equilibrium concentrations at higher dissolved solids concentrations decreased in the order isomaltose, isomaltotriose, kojibiose, nigerose, maltose, α, β‐Mrehalose, panose, and isomaltotetraose. They were not appreciably affected by changes in temperature or pH. A kinetic model based on adsorption of D‐glucose and the seven di‐ and trisaccharides by the first three glucoamylase subsites was formulated. Oligosaccharide formation was simulated with the model, using equilibrium data gathered for this article and subsite binding energies and kinetic parameters for oligosaccharide hydrolysis measured earlier. Agreement of simulated and actual oligosaccharide formation data through the course of the reaction was excellent except at very high solid concentrations.
On the coexistence of competing microbial species in a chemostat under cycling
Authors: Pavlou S. , Kevrekidis I. G. , Lyberatos G. 
Published: May 2005

AbstractIt is known that two microbial species competing for a single rate‐limiting nutrient cannot grow together in a chemostat under steady‐state operation, but eventually the species with the lower specific growth rate at the particular operating conditions will become extinct. Coexistence of the two populations has been shown obtainable in chemostats under periodic operation. This is possible in cases where the specific growth rate functions of the two species are such that for certain values of the nutrient concentration the first species grows faster than the second, and for other values of the nutrient concentration the second species is the one growing faster. In a previous article it was demonstrated that, even in cases where the specific growth rate functions of the two species are such that one of the species grows faster than the other for all values of the nutrient concentration, extinction of either species is possible provided that time delay in the response of the species to changes in their fermentation environment is accounted for, and that the faster growing species is also faster in its response. Here, we show that coexistence of the two species is also possible in a significant range of the operating parameters. We develop a numerical algorithm with which we trace the boundary of the coexistence region in the entire operating parameter space and construct the operating diagram of the system.
A modeling study of carbon and light limitation in algal biofilms
Authors: Liehr Sarah K. , Suidan Makram T. , Eheart J. Wayland 
Published: May 2005

AbstractIn an effort to develop an understanding of the interaction of inorganic carbon and light limitation in algal biofilms, a mathematical model was developed, based on well‐established mathematical descriptions of the biological, chemical, and physical processes involved. The results showed that the growth of algal biofilms is a very complex function of the inorganic carbon and light conditions, due to the interaction of inorganic carbon speciation with pH. These results are discussed in terms of the distribution of reaction rate through the biofilm and in terms of maximum potential growth rate for given bulk conditions.
Production, purification, and characterization of xylanase from a hyperxylanolytic mutant of Aspergillus ochraceus
Authors: Biswas S. R. , Jana S. C. , Mishra A. K. , Nanda G. 
Published: May 2005

AbstractEnhancement of the productivity of xylanase and β‐xy‐losidase of Aspergillus ochraceus was investigated by multistep mutagenesis. The spores of the wild strain were subjected to UV and N‐methyl‐N‐nitro‐N‐nitro‐soguanidine (NTG). The hyperxylanolytic mutant (NG‐13), which showed good clearing on the surface of the xylan‐agar plate, secretes xylanase and β‐xylosidase at high levels during growth on commercial xylan and on agricultural wastes. Both liquid and solid state cultures were employed in the study for enzyme production. The xylanase from NG‐13 was purified to homogeneity by ammonium sulfate precipitation and gel filtration. This purified enzyme showed a pH optimum of 6.0 and was stable in the range of pH 5 to 10. Prolonged stability of the enzyme was observed at 45°C though its activity was maximal at 50°C. The molecular weight of the enzyme was estimated to be 4.3 × 104 by SDS‐polyacrylamide gel electrophoresis and 5 × 104 by gel filtration on Sephadex G‐75. The kinetic data showed that the Km and Vmax values for xylan were 1 × 10−3M and 19.6 μmol/ min/mg protein, respectively. The enzyme was both more active and thermostable in the presence of K+and was inactivated by thiol reagents such as Hg2+, p‐hydroxymercuribenzoate (PHMB), 3′, 5′‐dithiobis (2′‐nitrobenzoic acid) (DTNB), and N‐ethylmaleimide (NEM).
The use of a single‐fiber reactor for the enzymatic removal of amino acids from solutions
Authors: Reiken Steven R. , Briedis Daina M. 
Published: May 2005

AbstractIn this article we describe the use of bench‐scale single‐fiber dialyzers for the development and testing of an immobilized enzyme reactor for the treatment of leukemia. The treatment is based on the enzymatic removal of specific amino acids from the blood of leukemia patients. L‐Lysine α‐oxidase and catalase were coimmobilized within the void space of the porous region of asymmetric hollow‐fiber membranes for the removal of L‐lysine from simulated human plasma solutions. Hollow‐fiber reactor performance was evaluated using a small single‐fiber dialyzer (SFD) consisting of a single fiber encased in a protective glass shell. This small reactor affords ease of use, requires small amounts of chemicals and biochemicals, and gives useful reactor performance data. Single‐fiber dialyzers were constructed using polyamide fibers with a molecular weight cutoff of 10,000 (PA10 fibers); these fibers demonstrated the best compatibility with and retention of the enzymes. The SFD performance in removing L‐lysine from solution was evaluated under both steady and pulsatile flow operation. Pulsatile flow was tested for two reasons: (1) to enhance the radial mass transfer of lysine within the SFD and (2) to simulate the pulsatile flow of blood in dialysis treatment. The use of pulsatile flow increased lysine conversion by 15% over the steady‐flow case. Approximately 40% of the lysine was removed from simulated plasma by the SFD in a 4‐h experiment using pulsatile flow in the recycle mode.
Diffusion of phenol through a biofilm grown on activated carbon particles in a draft‐tube three‐phase fluidized‐bed bioreactor
Authors: Fan L.‐S. , Leyva‐Ramos R. , Wisecarver K. D. , Zehner B. J. 
Published: May 2005

AbstractDiffusion of phenol through a biofilm attached to activated carbon particles was investigated. The biofilm was grown on activated carbon particles in a draft‐tube three‐phase fluidized‐bed bioreactor operating in a fed‐batch mode. It was found that phenol did not adsorb on the biofilm and that the diffusion coefficient of phenol within the biofilm varied from 13 to 39% of its corresponding value in water. The diffusion coefficient of phenol within the biofilm was reduced by increasing the biofilm density. An extensive literature review of diffusion of substrates through biofilms indicated that this conclusion could be extended to biofilms grown on flat surfaces, rotating cylinders, and even bioflocs.
Prediction of diffusion coefficients of proteins
Authors: Tyn Myo T. , Gusek Todd W. 
Published: May 2005

AbstractA correlation for predicting the diffusion coefficients of proteins at standard conditions is proposed by adapting the Stokes‐Einstein equation to a model for the equivalent hydrodynamic sphere. The radius of gyration, which accounts for the size and shape of protein molecules in solution, was used in deriving the new correlation. The correlation successfully predicted the diffusion coefficients of proteins, for which experimental data were available, with a higher degree of accuracy than achieved by previous correlation methods.
A process for the production of human proinsulin in Saccharomyces cerevisiae
Authors: Tøttrup Hanne V. , Carlsen Søren 
Published: May 2005

AbstractIn order to develop a large‐scale fermentation process for the production of human proinsulin in yeast, the intra‐cellular expression of a human superoxide dismutase‐human proinsulin fusion product (SOD‐PI) has been studied. The expression of SOD‐PI in Saccharomyces cerevisiae is regulated by a hybrid alcohol dehydrogenase 2/glyceraldehyde‐3‐phosphate dehydrogenase promoter. The promoter is repressed by glucose and derepressed by depletion of glucose. Although the genetic stability of the construction is shown to be poor under product‐inducing conditions, it is demonstrated in shake flask experiments that a stable expression potential can be maintained in a complex medium for more than 60 generations by maintaining excess glucose throughout the cultivations. These results have been confirmed in continuous cultures in chemostat and turbidostat experiments. Addition of the glucose analogs glucosamine, 2‐desoxyglucose, methylglucose, and thioglucose also leads to repression of SOD‐PI formation. The analogs, however, are not suitable for improving genetic stability during propagation because of growth inhibition. In batch fermentation experiments in a complex medium at 30°C, it has been demonstrated that initial glucose concentrations up to 50 g/L result in high specific SOD‐PI yields giving an overall yield of up to 700 mg SOD‐PI/L whereas higher glucose concentrations lead to both lower specific and overall yields due to depletion of critical medium components in the production period. In fed‐batch experiments at 30°C it has been possible to obtain high specific SOD‐PI yields even at high biomass concentrations by feeding glucose at a constant rate of 1.5 g/L/h for 40 h followed by a feeding of ethanol at 1.0 g/L/h for 24 h, thus giving an overall yield of 1200 mg/L. Decreasing the temperature from 30 to 26°C leads to improved yields in batch as well as fed‐batch experiments. The optimized fed‐batch fermentation process which is suitable to be scaled up to the cubic meter level has been tested in 200‐L fermentations resulting in yields of more than 1500 mg/L of the fusion protein which conveniently can be used as a precursor in the production of recombinant human proinsulin.
Mechanism of enhanced oxygen transfer in fermentation using emulsified oxygen‐vectors
Authors: Rols J. L. , Condoret J. S. , Fonade C. , Goma G. 
Published: May 2005

AbstractLimitations of oxygen transfer in fermentation can be solved using auxiliary liquids immiscible in the aqueous phase. The liquids (called oxygen‐vectors) used in this study were hydrocarbon (n‐dodecane) and perfluorocarbon (forane F66E) in which oxygen is highly soluble (54.9 mg/L in n‐dodecane and 118 mg/L in forane F66E at 35°C in contact with air at atmospheric pressure). It has been demonstrated that the use of n‐dodecane emulsion in a culture of Aerobacter aerogenes enabled a 3. 5‐fold increase of the volumetric oxygen transfer coefficient(kLa) calculated on a per‐liter aqueous phase basis. The droplet size of the vector played a crucial role in the phenomena. When a static contact between gas bubble and vector droplet was established in water, the vector covered the bubble, in agreement with positive values of the spreading coefficient for these fluids. The determination of the oxygen transfer coefficients (kL) in a reactor with a definite interfacial area enabled the main resistance to be located in the boundary layer of the waterside either for a gas‐water or a vector‐water interface. Because oxygen consumption by weakly hydrophobic cells can only occur in the aqueous phase, the oxygen transfer is achieved according to the following pathway: gas‐vector‐water‐cell. Finally, a mechanism for oxygen transfer within this four‐phased system is proposed.
Mass transfer phenomena in an airlift reactor: Effects of solids loading and temperature
Authors: Smith Bryan C. , Skidmore Duane R. 
Published: May 2005

AbstractGas holdups and volumetric mass transfer coefficients were measured in a concentric tube airlift reactor designed for the microbial desulfurization of coal. The solutions studied were comprised of an acidified basal salts solution containing thirteen different weight percentages (0 to 40) of coal (74 μm Ohio #1) at three different temperatures (30, 50, and 72°C). Gas holdup ϵG decreased with solids loading for the entire range studied. An enhancement in the volumetric mass transfer coefficient KLa with respect to that in pure solution was observed from zero to approximately 5 wt % (solids volume fraction ϵs = 0.035), the maximum enhancement occurring at approximately 2 wt % (ϵs = 0.014). At higher solids fractions, the mass transfer coefficient decreased with further solids additions. Gas holdups and the mass transfer coefficients increased with temperature over the studied range. The KLa and ϵG were correlated to three process variables separately and the separate correlations combined to yield generalized correlations for the mass transfer coefficient and gas holdup for this system. The correlations may be used for design, operation, and ost estimation of such systems.
Effect of biofilm growth on steady‐state biofilm models
Authors: Skowlund Christopher T. 
Published: May 2005

AbstractThe results of numerical simulations for a growing biological film are presented to justify the use of steady‐state biofilm models for approximating the behavior of both unlimited and shear‐limited biofilms. For an unlimited biofilm we show that although the total biofilm thickness may continue to increase over time, the active biofilm volume will reach a constant value. We also show that the profile of active microorganisms within the biofilm will become constant with respect to the biofilm/fluid interface and simply move outward as the biofilm thickness increases. For a shear‐limited biofilm we similarly show that once a “limiting” thickness has been reached the active biofilm volume, substrate consumption, and profile of active microorganisms within the biofilm will also be independent of the biofilm thickness.
Kinetic model for microbial uptake of insoluble solid‐state substrate
Authors: Huang Shih‐Yow , Chou Ming‐Shean 
Published: May 2005

AbstractA kinetic model for anaerobic digestion of insoluble solid‐state substrates was developed. Rate equations for cell growth and substrate consumption were derived based on the assumption that the microorganisms assimilate the substrate mainly at the point of contact where they grow. The model emphasizes effects of substrate particle size, organic loading, and cell concentration on the rates of cell growth and substrate utilization. Batch digestion of a stearic acid emulsion with a mean particle size of 2.0 μm and a biological sludge was conducted at 30 and 37°C to verify the proposed model. Agreement between the experimental and calculated results indicated the validity of the model for describing the microbial degradation of insoluble solid‐state substrates. Further examinationof the model revealed that with low cell substrate affinity or at low cell concentration, it coincided with a Michaelis–Menten type kinetics in which the effect of particle size was taken into consideration.
Immobilized cell biocatalyst activation and pseudo‐steady‐state behavior: Model and experiment
Authors: Monbouquette H. G. , Sayles G. D. , Ollis D. F. 
Published: May 2005

AbstractAn intrinsic, unstructured model has been utilized to describethe startup dynamics of a continuous Caalginate‐immobilized Zymomonas mobilis (ATCC 10988) fermentation. This model predicts, at least qualitatively, transients in the fermenter effluent glucose, ethanol, and biomass concentrations as well as radial gradients in immobilized‐cell concentration and activity within the gelbiocatalysts. Predicted intrabiocatalyst gradients in immobilized‐cell specific growth rate were used to calculate the corresponding gradients in intracellular RNA level based on a reported linear relationship between the two. Mathematical simulations of immobilized biomass concentration profiles and RNA content were verified using a novel, scanning microfluorimetry technique.
Comparison of simultaneous wet milling and enzymatic hydrolysis of cellulose in ball mill and attrition mill reactors
Authors: Furcht P. W. , Silla H. 
Published: May 2005

AbstractSimultaneous wet milling and enzymatic hydrolysis of newsprint in a ball mill reactor (BMR) and in an attrition mill reactor (AMR) were studied. The effect of milling on the enzyme deactivation was also investigated. Variables studied included milling media size, material, and the presence or absence of an air–liquid interface in the reactor. At a reaction temperature of 45°C and a pH of 4.5 and in the presence of an air–liquid interface, the amount of reducing sugars produced by hydrolysis using a BMR was typically 5 to 15%less than the amount produced using an AMR. Without an air–liquid interface there was no significant difference. The effect of an air–;liquid interface on enzyme deactivation without any substrate was also studied. Enzyme activity after six hours of milling ranged from 1 to 85% ofthe starting activity. In both the AMR and the BMR, the extent of enzyme deactivation was 20 to 50% greater with an air–liquid interface present than with the air–liquid interface absent.
Production of indole alkaloids by surface immobilized C. roseus cells
Authors: Archambault J. , Volesky B. , Kurz W. G. W. 
Published: May 2005

AbstractA technique was developed to surface immobilize plant cells and was scaled up in laboratory size bioreactors. This technique was shown not to hinder the biosynthetic potential of Catharanthus roseus immobilized cells and to induce a partial release (300 μg/L) of serpentine into the culture medium contrary to suspension cultured cells. The release pattern seemed to follow the biosynthesis trends of the product. This release mechanism could be stimulated by a factor of 10 within 2 h by increasing the pH of the culture from 5.0 to 5.5.
Plasmid‐encoded protein: The principal factor in the “metabolic burden” associated with recombinant bacteria
Authors: Bentley William E. , Mirjalili Noushin , Andersen Dana C. , Davis Robert H. , Kompala Dhinakar S. 
Published: May 2005

AbstractExperimental elucidation of the metabolic load placed on bacteria by the expression of foreign protein is presented. The host/vector system is Escherichia coli RR1/pBR329 (ampr, camr, and letr). Plasmid content results, which indicate that the plasmid copy number monotonically increases with decreasing growth rate, are consistent with the literature on ColE1‐like plasmids. More significantly, we have experimentally quantified the reduction in growth rate brought about by the expression of chloramphenicol‐acetyl‐transferase (CAT) and β‐lactamase. Results indicate a nearly linear decrease in growth rate with increasing foreign protein content. Also, the change in growth rate due to foreign protein expression depends on the growth rate of the cells. The observed linear relationship is media independent and, to our knowledge, previously undocumented. Furthermore, the induction of CAT, mediated by the presence of chloramphenicol, is shown to occur only at low growth rates, which further increases the metabolic load.Results are vdelineated with the aid of a structured kinetic model representing the metabolism of recombinant E. coli. In this article, several previous hypotheses and model predictions are justified and validated. This work provides an important step in the development of comprehensive, methabolically‐structured, kinetic models capable of prediciting optimal conditions for maximizing product yield.
Enzyme production by genetically engineered Streptomyces strains: Influence of culture conditions
Authors: Erpicum Thomas , Granier Benoît , Delcour Marianne , Lenzini V. Mauro , Nguyen–Distèche Marline , Dusart Jean , Frère Jean–Marie 
Published: May 2005

AbstractProduction of various extracellular enzymes (the β‐lactamases from Streptomyces albus G, Streptomyces cacaoi, Actinomadura R39, and the DD‐carboxypeptidase from Streptomyces R61) by genetically engineered Streptomyces lividans TK24 in Lennox broth medium reached a maximum after 36 to 48 h. Subsequently, the enzyme activity drastically decreased probably due to an increased pH value and the production of an inactivator by Streptomyces lividans. Protease activity did not seem to play a major role. The increased pH and inactivator synthesis are related to amino acid catabolism and generally result in cellularlysis. The use of a medium where the catabolism of amino acids was made less likely by the presence of glucose and NH4Cl and by buffering at pH 7.4 considerably inproved the yield. Furthermore, the water activity of the medium seemed to be an important parameter for the production of extracellular proteins by genetically engineered Streptomyces. Better production was observed when the water activity was decreased to 0.96–0.98 by addition of sucrose.Under those conditions, the concentration of extracellular enzyme reached about 0.3 g (1 g in the best case)/L of culture supernantant.
Optimum ph and temperature conditions for xylose fermentation by Pichia stipitis
Authors: Slininger P. J. , Bothast R. J. , Ladisch M. R. , Okos M. R. 
Published: May 2005

AbstractPichia stipitis NRRL Y‐7124 is a xylose‐fermenting yeast able to accumulate ca. 57 g/L ethanol. Because optimum process conditions are important, data were collected to determine the effects of temperature and pH on growth and fermentation rates and product accumulations. Temperatures (26–35°C) providing optimum biomass and ethanol productivities did not necessarily provide maximum ethanol accumulation. Xylitol and residual xylose concentrations increased with temperature. Maximum ethanol selectivity was achieved at 25–26°C with minimal sacrifice to production rates. The temperature optimum for xylose could not be generalized to glucose fermentations, in which ethanol productivity and accumulation were optimum at 34°C. The optimum pH range for growth and fermentation on xylose was 4–7 at 25°C.