bluuebunny/crossref_metadata_2025_split huggingface dataset:
Substrate conditions that influence the assays used for determining the β‐glucosidase activity of cellulolytic microorganisms
Authors: Breuil C. , Mayers P. , Saddler J. N. 
Published: December 2004

AbstractCulture filtrates from Trichoderma harzianum E58, T. reesei CL 847 and Penicillium sp. C 462 were assayed for β‐glucosidase activity using a range of substrates and sugar analysis methods. Although sugar analyses by the dinitrosalicylic acid (DNS) and Nelson–Somogyi methods gave a similar profile, when increasing concentrations of salicin were assayed, considerably higher values were obtained with the DNS assay. The salicin concentration used for the assay greatly influenced the final β‐glucosidase values with higher values obtained for T. harzianum E58 and T. reesei CL 847 at substrate concentrations of 1 mg/mL while optimum values for Penicillium sp. C 462 were obtained at substrate concentrations greater than 3 mg/mL. Low concentrations of salicin and p‐nitro‐phenyl‐β‐D‐glucopyranoside (PNPG) gave the same response as cellobiose. Cellobiose should be used at concentrations greater than 3.74 mg/mL to avoid substrate limitation of the β‐glucosidase assay.
Regeneration of NAD+ cofactor by photosensitized electron transfer in an immobilized alcohol dehydrogenase system
Authors: Julliard M. , Le Petit J. , Ritz P. 
Published: December 2004

AbstractThe irradiation with visible light of a photosensitizer dye like methylene blue was used to regenerate by electron transfer the oxidized form of a pyridine nucleotide coenzyme (NAD+). The process has been studied on a common enzymatic reaction: ethanol oxidation by alcohol–NAD+ oxidoreductase immobilized on polyacrylamide gel or porous glass balls. In the experimental conditions used, the initial NAD+ recycling rates were 2.33 × 104 cycles/h (polyacrylamide) and 3 × 104 cycles/h (glass balls). A total number of 49.5 × 104 cycles was obtained for 13 runs of 2 h. The enzyme immobilization strongly increased its stability: after 28 days at 20°C, the residual activity was 25% of the initial value.
Production of the macrolide antibiotic tylosin in cyclic fed‐batch culture
Authors: Gray P. P. , Vu‐Trong K. 
Published: December 2004

AbstractTylosin‐producing Streptomyces fradiae was cultured on a synthetic medium with a high glutamate–glucose ratio. Tylosin batch fermentations with this medium were characterized by a high initial specific production rate of tylosin (qtylosin, mg/g h) that decreased as the fermentation progressed. Continuous feeding of glutamate, glucose, and methyloleate at a constant feed rate initiated during the period of high qtylosin had been shown to produce some increase in tylosin productivity. By using a cyclic feeding strategy, it was possible to increase tylosin productivity further. Tylosin fed‐batch fermentations with glutamate and glucose being fed to the culture in cyclic square‐wave profiles with methyloleate in excess showed several‐fold increase in final qtylosin and tylosin titers. By varying cycle amplitudes and period of the substrates, it was found that maximum tylosin productivity occurred when the glutamate cycle amplitude was 600 mg/L and that of glucose was 42.5 mg/L per cycle period of 24 h. With these cycle amplitudes of glutamate and glucose, the tylosin cyclic fed‐batch culture also showed high cellular uptake of methyloleate. Decreasing or increasing glucose cycle amplitude at fixed glutamate amplitude lowered tylosin production, and no further stimulation of tylosin synthesis was observed when α‐ketoglutarate was supplemented to the cyclic substrate feeds. Under optimum cyclic conditions it was possible to maintain linear tylosin accretion and a constant value of qtylosin up to 240 h.
Prevention of formation of acid drainage from high‐sulfur coal refuse by inhibition of iron‐ and sulfur‐oxidizing microorganisms. I. Preliminary experiments in controlled shaken flasks
Authors: Dugan P. R. 
Published: December 2004

AbstractChanges of pH and sulfate concentration in high‐sulfur coal refuse slurries are used as measurements of microbial pyrite oxidation in the laboratory. Sodium lauryl sulfate (SLS), alkylbenzene sulfonate (ABS), benzoic acid (BZ) and combinations of SLS plus BZ and ABS plus BZ effectively inhibited formation of sulfate and acid when added in concentrations greater than 50 mg/L to inoculated 20 or 30% coal refuse slurries. Here 25 mg/L concentrations of SLS, ABS, and ABS + BZ stimulated acid production. Formic, hexanoic, oxalic, propionic, and pyruvic acids at 0.1% concentrations were also effective inhibitors. Four different lignin sulfonates were only slightly effective inhibitors at 0.1% concentrations. It was concluded that acid formation resulting from microbial oxidation in high‐sulfur coal refuse can be inhibited.
Performance of the duckweed species Lemna gibba on municipal wastewater for effluent renovation and protein production
Authors: Oron Gideon , Porath Dan , Jansen Hans 
Published: December 2004

AbstractAn outdoor experiment was conducted in miniponds to evaluate the performance of Lemna gibba, a duckweed species, as a domestic wastewater stripper. Duckweed is one of the floating plants with a high capability of ammonia uptake and assimilation rate into valuable protein. The results indicate that under adequate operational conditions, depending mainly on the organic loading, the effluent quality meets irrigation reuse criteria and protein yield of the duckweed may reach 12 ton/ha per year, far above other conventional field crops.
Modeling and analysis of diffusion and reaction in legume nodules
Authors: Jones G. T. , Davis L. C. , Ghosh Hajra A. K. , Erickson L. E. 
Published: December 2004

AbstractDiffusion of gases through legume nodules is important for nitrogen fixation. A mathematical model is presented for diffusion and enzymatic reaction for legume nodules with a reactive core and an inert shell. The transient model is solved numerically for spherical geometry for acetylene reduction by nitrogenase enzyme. The results are used to estimate the diffusivities of acetylene and ethylene in the nodules by comparing predicted and experimental lag times. The experimental results are also analyzed using an effectiveness factor plot for spherical nodules with inert shells and reactive cores. The results show that the diffusivities are slightly higher than those for acetylene and ethylene in water because of some contribution of gas phase diffusion. Applications to oxygen diffusion through nodule tissue are suggested.
Citric acid production using immobilized conidia of Aspergillus niger TMB 2022
Authors: Tsay S. S. , To K. Y. 
Published: December 2004

AbstractConidia of Aspergillus niger TMB 2022 were immobilized in calcium alginate for the production of citric acid. A 1‐mL conidia suspension containing ca. 2.32 × 108 conidia were entrapped into sodium alginate solution in order to prepare 3% Ca–alginate (w/v) gel bead. Immobilized conidia were inoculated into productive medium containing 14% sucrose, 0.25% (NH4)2CO3, 0.25% KH2PO4, and 0.025% MgSO4·7H2O with addition of 0.06 mg/L CuSO4·5H2O, 0.25 mg/L ZnCl2, 1.3 mg/L FeCl3·6H2O, pH 3.8, and incubated at 35°C for 13 days by surface culture to produce 61.53 g/L anhydrous citric acid. Under the same conditions with a batchwise culture, it was found that immobilized conidia could maintain a longer period for citric acid production (31 days): over 70 g/L anhydrous citric acid from runs No. 2–4, with the maximum yield for anhydrous citric acid reaching 77.02 g/L for run No. 2. In contrast, free conidia maintained a shorter acid‐producing phase, ca. 17 days; the maximum yield for anhydrous citric acid was 71.07 g/L for run No. 2 but dropped quickly as the run number increased.
A model for growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media
Authors: Sardonini Charles A. , DiBiasio David 
Published: December 2004

AbstractA major problem in the use of plasmids as recombinant vectors is the problem of plasmid‐free cell generation from plasmid shedding and subsequent growth. A common technique for controlling the population of plasmidfree cells is the use of selective media against these cells using an auxotrophic host and a plasmid that has the ability to produced the essential metabolite. A distributed model describing the growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media was developed. The model allows for growth and production of a metabolite by the plasmid‐carrying strain and growth of the plasmid‐free cells on resulting metabolite concentrations. Through a determination of system constants and numerical solution to the equations, experimental batch and continuous culture results for cell concentration transients could be simulated by the model. The results indicated that despite selective pressure, plasmid‐free cell growth was significant.
Continuous production of L‐phenylalanine by transamination
Authors: Ziehr H. , Kula M.‐R. , Schmidt E. , Wandrey C. , Klein J. 
Published: December 2004

AbstractL‐Phenylalanine was produced continuously from L‐as‐partate and phenylpyruvate by transaminase from a newly screened Pseudomonas putida strain. The process was carried out with an isolated enzyme in homogeneous phase in an enzyme membrane reactor and with immobilized whole cells in a stirred tank reactor, respectively. Due to the difference in transport resistance, the productivity of the free enzyme in homogeneous phase (72 mmol/L h) was about 3 times higher than the productivity achieved using immobilized cells. However, a better stability of the biocatalyst was observed with immobilized cells.
A new method to determine active enzyme distribution, effective diffusivity, rate constant for main reaction and rate constant for deactivation
Authors: Do D. D. , Hossain Md. M. 
Published: December 2004

AbstractA new method is presented to determine (1) the rate constant for the main reaction, (2) the rate constant for deactivation, (3) the effective diffusivity, and (4) the active enzyme distribution within a porous solid support by utilizing data of bulk substrate concentration versus time in a continuous stirred basket reactor. The method relies on an assumption of parallel deactivation mechanism with strong pore diffusional resistance with respect to substrate species. The data of hydrogen peroxide‐immobilized catalase published in the literature are used to demonstrate the theory. A parameter determination procedure is also presented.
Kinetics of milk coagulation: I. The kinetics of kappa casein hydrolysis in the presence of enzyme deactivation
Authors: Carlson Alfred , Hill Charles G , Olson Norman F. 
Published: December 2004

AbstractThe kinetics of the primary phase of the enzymatic coagulation of milk, i.e., κ‐casein hydrolysis, was investigated in the presence and in the absence of concurrent enzyme deactivation processes. For conditions under which the enzyme is stable, the rate of hydrolysis can be described by Michaelis–Menten kinetics, as has been reported by previous investigators. A mathematical model, experimental data, and parameter estimates are provided for κ‐casein hydrolysis in the presence of concurrent deactivation of enzyme. The model accurately describes the experimental results when porcine pepsin was used as the renneting enzyme. The model and the experimental results indicate that samples of milk treated under conditions where deactivation of enzyme is significant can have fractional conversions of κ‐casein ranging from zero to unity and yet contain no active enzyme at the termination of the treatment.
Modeling and analysis of radial flow mammalian cell culture
Authors: Tharakan John P. , Chau Pao C. 
Published: December 2004

AbstractA model for radial flow mammalian cell culture has been developed. Two situations, one with permeable hollow fibers and the other with a porous matrix in the annulus, were considered. The hollow fibers were modeled as continuously distributed sinks. Numerical solutions are presented for the complete model as well as limiting analytical solutions. The analysis identified the importance of various kinetic, transport, and design dimensionless groups for maintenance of radial flow cell culture systems under uniform conditions. The important design parameter was the depth of the bed and the important operating parameter was a modified Damkohler number, both of which should be maintained low for gradient free systems. Dispersion was included in the analysis but substrate consumption was relatively independent of dispersion. Preliminary separation of a low‐and high‐molecular‐weight product was also modeled, and shown to be strongly dependent on the permeability of the fibers, as well as the aspect ratio and the magnitude of the transmembrane flux.
Determination of the intrinsic kinetic constants of immobilized glucose oxidase and catalase
Authors: Tse Pius H. S. , Leypoldt John K. , Gough David A. 
Published: December 2004

AbstractModels of membrane systems containing immobilized glucose oxidase and catalase operating together or independently have been developed. A rotated disk electrode apparatus was employed with novel electrochemical operating conditions to experimentally determine mass transfer and intrinsic kinetic parameters of enzyme‐containing membranes. The value of a mass transfer parameter that describes internal and external diffusion was first determined under conditions that do not permit the enzyme reactions. In a subsequent experiment with the reaction allowed, kinetic parameters corresponding to the intrinsic maximal velocity and Michaelis constants of the immobilized enzymes were estimated by regression analysis of data based on an appropriate two‐ or three‐ parameter model. It was found that immobilization reduced the maximal intrinsic velocity but had no detectable effect on the Michaelis constants. In all but one case‐ these methods for membrane characterization are nondestructive and can be used repeatedly on a given membrane. These techniques provide the means for quantitative comparisons of immobilization methods and make possible temporal studies of immobilized enzyme inactivation.
Time‐dependent inactivation of immobilized glucose oxidase and catalase
Authors: Tse Pius H. S. , Gough David A. 
Published: December 2004

AbstractHomogeneous membranes containing immobilized glucose oxidase and catalase were stored in buffered solutions at 37°C to determine the mechanisms and rates of catalyst inactivation. The experiments were designed so that inactivation occurred homogeneously throughout the membrane, thereby simplifying the analysis. The mechanism of inactivation is consistent with the reaction of hydrogen peroxide and certain catalytic intermediates of both enzymes. Based on this information, numerical simulations were developed that incorporate spatially heterogeneous catalytic and inactivation processes.
Kinetics and bioenergetics of light‐limited photoautotrophic growth of Spirulina platensis
Authors: Lee H. Y. , Erickson L. E. , Yang S. S. 
Published: December 2004

AbstractBlue–green algae, Spirulina platensis, is cultivated under photoautotrophic growth conditions designed to have nearly uniform growth rate throughout the fermentor by illumination both sides of a rectangular vessel. The results show that growth rate and bioenergetic yield are a function of light intensity. Several kinetic models are considered to express the relationship between growth rate and light intensity.
Static characteristics of a continuous flow bioreactor containing antibiotic‐resistant recombinant cells
Authors: Chang Yong K. , Lim H. C. 
Published: December 2004

AbstractThe steady‐state behavior of a continuous bioreactor containing antibiotic‐resistant recombinant cells has been investigated. Only the plasmid‐free cell is susceptible to and killed by antibiotics. A Monod form of specific death rate was found to simulate quite well the experimental death rates of various cells due to antibiotics. The stability characteristics, including bifurcation of the possible steady states, are examined. Appropriate numerical illustrations for the steady‐state characteristics have been provided. Theoretically, two coexistence steady states (CO), three partial washout steady states (PW), and one total washout steady state (TW) are feasible, but only one CO, one PW, and one TW were realized. When antibiotic consumption is not extremely significant the CO can exist over one or two ranges of dilution rates depending upon the antibiotic concentration in the feed. The CO is globally stable. Whenever the PW and/or the TW exist(s) together with the CO they are unstable. Sensitivity analyses for several key kinetic parameters have been made. The rate at which the plasmid‐bearing cells revert to the plasmid‐free cells has the most significant effect on the antibiotic susceptibility of the system. Some simplified optimization calculations for maximum profit have been carried out.
A process for protein enrichment of cassava by solid substrate fermentation in rural conditions
Authors: Daubresse P. , Ntibashirwa S. , Gheysen A. , Meyer J. A. 
Published: December 2004

AbstractAn artisanal static process for protein enrichment of cassava by solid‐state fermentation, developed in laboratory and tested on pilot units in Burundi (Central Africa), provides enriched cassava containing 10.7% of dry matter protein versus 1% before fermentation. Cassava chips, processed into granules of 2–4‐mm diameter, are moistened (40% water content) and steamed. After cooling to 40°C, cassava is mixed with a nutritive solution containing the inoculum (Rhizopus oryzae, strain MUCL 28627) and providing the following per 100 g dry matter: 3.4 g urea, 1.5 g KH2PO4, 0.8 g MgSO4·7H2O, and 22.7 g citric acid. For the fermentation, cassava, with ca. 60% moisture content, is spread in a thin layer (2–3 cm thick) on perforated trays and slid into an aerated humidified enclosure. The incubation lasts ± 65 h. The production of protein enriched cassava is 3.26 kg dry matter/m2tray. The effects of the variation of the nutritive solution composition and the inoculum conservation period on the protein production are equally discussed.
Cadmium accumulation by a Citrobacter sp. immobilized on gel and solid supports: Applicability to the treatment of liquid wastes containing heavy metal cations
Authors: Macaskie L. E. , Wates J. M. , Dean A. C. R. 
Published: December 2004

AbstractPolyacrylamide gel‐immobilized cells of a Citrobacter sp. removed cadmium from flows supplemented with glycerol 2‐phosphate, the metal uptake mechanism being mediated by the activity of a cell‐bound phosphatase that precipitates liberated inorganic phosphate with heavy metals at the cell surface. The constraints of elevated flow rate and temperature were investigated and the results discussed in terms of the kinetics of immobilized enzymes. Loss in activity with respect to cadmium accumulation but not inorganic phosphate liberation was observed at acid pH and was attributed to the pH‐dependent solubility of cadmium photsphate. Similarly high concentrations of chloride ions, and traces of cyanide inhibited cadmium uptake and this was attributed to the ability of these anions to complex heavy metals, especially the ability of CN− to form complex anions with Cd2+. The data are discussed in terms of the known chemistry of chloride and cyanide‐cadmium complexes and the relevance of these factors in the treatment of metal‐containing liquid wastes is discussed. The cells immobilized in polyacrylamide provided a convenient small‐scale laboratory model system. It was found that the Citrobacter sp. could be immobilized on glass supports with no chemical treatment or modification necessary. Such cells were also effective in metal accumulation and a prototype system more applicable to the treatment of metal‐containing streams on a larger scale is described.
Rules for optimization of biocatalysis in organic solvents
Authors: Laane Colja , Boeren Sjef , Vos Kees , Veeger Cees 
Published: December 2004

AbstractGeneral rules for the optimization of different biocatalytic systems in various types of media containing organic solvents are derived by combining data from the literature, and the logarithm of the partition coefficient, log P, as a quantitative measure of solvent polarity. (1) Biocatalysis in organic solvents is low in polar solvents having a log P < 2, is moderate in solvents having a log P between 2 and 4, and is high in a polar solvents having a log P > 4. It was found that this correlation between polarity and activity parallels the ability of organic solvents to distort the essential water layer that stabilizes the biocatalysts. (2) Further optimization of biocatalysis in organic solvents is achieved when the polarity of the microenvironment of the biocatalyst (log Pi) and the continuous organic phase (log Pcph) is tuned to the polarities of both the substrate (log Ps) and the product (log Pp) according to the following rules: |log Pi − log Ps| and |log Pcph − log Pp| should be minimal and |log Pcph − log Ps| and |log Pi − log Pp| should be maximal, with the exception that in the case of substrate inhibition log Pi, should be optimized with respect to log Ps In addition to these simple optimization rules, the future developments of biocatalysis in organic solvents are discussed.
Use of epifluorescence microscopy for characterizing the activity ofThiobacillus Ferrooxidanson iron pyrite
Authors: Yeh Timothy Y. , Godshalk John R. , Olson Gregory J. , Kelly Robert M. 
Published: December 2004

AbstractThe enumeration and characterization of microorganisms attached to solid surfaces have always presented significant difficulties. This is particularly true for micro organisms that are indigenous to coal mines and mineral deposits where metal sulfides are ubiquitous. The complications that arise are the result of the variety of inorganic compounds that are present in these environments, the harsh conditions under which the microorganisms proliferate, and the low cell densities to which they grow. The work presented here suggests that epifluorescence microscopy using acridine orange can be a useful probe to study acidophilic metal‐leaching bacteria. Experiments involving the growth ofThiobacillus ferrooxidanson iron pyrite are described which indicate a relationship between cell fluorescence color and bacterial activity. Both attached and free‐solution cell densities were determined throughout the course of the leaching process and considered along with changes in cell fluorescence color which might be associated with changes in intracellular pH. As such, epifluorescence microscopy, using acridine orange, can be used for assessing the activity ofT. ferrooxidanson iron pyrite as well as resolving the controversy concerning the significance of attachment during the leaching process.