bluuebunny/crossref_metadata_2025_split huggingface dataset:
Steam‐explosion pretreatment of wood: Effect of chip size, acid, moisture content and pressure drop
Authors: Brownell H. H. , Yu E. K. C. , Saddler J. N. 
Published: May 2005

AbstractMaterial balances for pentosan, lignin, and hexosan, during steam‐explosion pretreatment of aspenwood, showed almost quantitative recovery of cellulose in the water‐insoluble fraction. Dilute acid impregnation resulted in more selective hydrolysis of pentosan relative to undesirable pyrolysis, and gave a more accessible substrate for enzymatic hydrolysis. Thermocouple probes, located inside simulated aspenwood chips heated in 240°C‐saturated steam, showed rapid heating of air‐dry wood, whereas green or impregnated wood heated slowly. Small chips, 3.2 mm in the fiber direction, whether green or airdry gave approximately equal rates of pentosan destruction and solubilization, and similar yields of glucose and of total reducing sugars on enzymatic hydrolysis with Trichoderma harzianum. Partial pyrolysis, destroying one third of the pentosan of aspenwood at atmospheric pressure by dry steam at 276°C, gave little increase in yield of reducing sugars on enzymatic hydrolysis. Treatment with saturated steam at 240°C gave essentially the same yields of glucose and of total reducing sugars, and the same yields of butanediol and ethanol on fermentation with Klebsiella pneumoniae, whether or not 80% of the steam was bled off before explosion and even if the chips remained intact, showing that explosion was unnecessary.
Diffusion coefficients of glucose and ethanol in cell‐free and cell‐occupied calcium alginate membranes
Authors: Hannoun Betty J. M. , Stephanopoulos Gregory 
Published: May 2005

AbstractThe diffusivities of glucose and ethanol in cell‐free and cell‐occupied membranes of calcium alginate were measured in a diffusion cell. The lag time analysis was used. Diffusivities decreased with increasing alginate concentration and were comparable with those in water for a 2% alginate membrane. Glucose and ethanol concentrations had no effect on the respective diffusion coefficients. The ratio of ethanol diffusivity to glucose diffusivity in 2 and 4% alginate agreed closely with the inverse ratio of the hydrodynamic raii for the two molecules in water, indicating that the hydrodynamic theory of diffusion in liquids may be applicable to diffusion in dilute alginate gels. Also, the presence of 20% dead yeast cells had no effect on the diffusivities. The data reported can be used to study reaction and diffusion in immobilized cell reactors and cell physiology under immobilized conditions.
Kinetics of batch fermentations for ethanol production with Zymomonas mobilis growing on Jerusalem Artichoke juice
Authors: Favela‐Torres E. , Allais J.‐J. , Baratti J. 
Published: May 2005

AbstractA flocculent strain of Zymomonas mobilis was used for ethanol production from Jerusalem Artichoke juice containing 113–245 g/L sugar in batch fermentation. The kinetic and yields parameters are calculated using a new method based on polynomial equations for the variation of biomass, ethanol, and sugar concentrations with time. The results show that. Z. mobilis can convert rapidly and efficiently Jerusalem Artichoke juice to ethanol. When a sugar concentration of 248 gL was used, 100 g/L ethanol was formed with an ethanol yield based on sugar utilized of 0.47 g/g (92% of theoretical LP).
Fermentation kinetics of Zymomonas mobilis at high ethanol concentrations: Oscillations in continuous cultures
Authors: Jöbses I. M. L. , Egberts G. T. C. , Luyben K. C. A. M. , Roels J. A. 
Published: May 2005

AbstractSubstrate‐limited continuous culture results at 47 g/L ethanol show that the maintenance factor and the yield factor of an unstructured maintenance model are lower compared to the values at 23 g/L ethanol. Computing the results according to a structured two‐compartment model predicts an enhanced turnover rate of the K‐compartment (RNA fraction) by ethanol, resulting in a lower steady‐state amount of K‐compartment. This is in agreement with experimentally determined RNA fractions. The parameters of both models respond qualitatively in the same way to elevation of the ethanol concentration as to elevation of the temperature. In product‐inhibited continuous cultures, at ethanol concentrations above 55 g/L, nearly sustained oscillations in biomass, substrate, and products were observed. The maximum ethanol concentration achieved in these continuous cultures was 70 g/L. The oscillations could be described by a structured mathematical model, in which ethanol inhibits the maximum specific growth rate indirectly by inhibiting the synthesis of an internal growth‐rate‐determining compound.
Analysis of unstable recombinant Saccharomyces cerevisiae population growth in selective medium
Authors: Srienc Friedrich , Campbell J. L. , Bailey J. E. 
Published: May 2005

AbstractWidely applied selection strategies for plasmid‐containing cells in unstable recombinant populations are based upon synthesis in those cells of an essential, selection gene product. Regular partitioning of this gene product combined with asymmetric plasmid segregation produces plasmid‐free cells which retain for some time the ability to grow in selective medium. This theory is elaborated here in terms of a segregated model for an unstable recombinant population which predicts population growth characteristics and composition based upon experimental data for stable strain growth kinetics, plasmid content, and selection gene product stability. Analytical solutions from this model are compared with an unsegregated phenomenological model to evaluate the effective specific growth rate of plasmid‐free cells in selective medium. Model predictions have been validated using experimental growth kinetics and flow cytometry data for Saccharomyces cerevisiae D603 populations containing one of the plasmids YCpG1ARS1, YCpG1ΔR8, YCpG1ΔR88, YCpG1ΔH103, YCpG1ΔH200, pLGARS1, and pLGSD5. The recombinant strains investigated encompass a broad range of plasmid content (from one to 18 plasmids per cell) and probability α of plasmid loss at division (0.05 ≤ α ≤ 0.42). Experimental data for all strains considered is inconsistent with the hypothesis that plasmid‐free cells are unable to grow in selective medium. For a given value of a, the fraction of plasmid‐containing cells in the population decreases with increasing plasmid content and increases for less stable selection gene products. This conceptual framework and mathematical model will aid in strain development for greater effective stability.
Enzymatic formation of propylene bromohydrin from propylene by glucose oxidase and lactoperoxidase
Authors: Kawakami Koei , Nagamatsu Shigeki , Ishii Masuki , Kusunoki Koichiro 
Published: May 2005

AbstractThe time course of the peroxidative bromination of propylene accompanied by in situ generation of hydrogen peroxide by glucose oxidase was examined to improve the productivity of propylene bromohydrin. To prevent the rapid inactivation of lactoperoxidase by excess hydrogen peroxide, it was effective to use lactoperoxidase in large excess as compared with glucose oxidase, and to raise the concentration of bromide ion. However, the rate of glucose consumption was lowered at high concentrations of bromide ion, and at higher mole fraction of oxygen as compared with propylene in the gas mixture. Therefore, it seemed that for the favorable production of bromohydrin there existed the optimal conditions for the concentration of bromide ion and for the composition of oxygen‐propylene gas mixture. Such kinetic behaviors of the sequential enzymatic reactions were explained by a mechanism involving free hypobromous acid as a reactive intermediate. Furthermore, the stability of the coimmobilized enzymes with k‐carrageenan gels was investigated in continuous operations. The half‐life of the enzymes was ca. 60 h for the production of propylene bromohydrin.
Detailed study of anaerobic digestion of Spirulina maxima algal biomass
Authors: Samson Réjean , Leduyt Anh 
Published: May 2005

AbstractBiomass of the blue–green alga Spirulina maxima was converted to methane using continuous stirred tank digesters with an energy conversion efficiency of 59%. Digesters were operated using once‐a‐day feeding with a retention time (θ) between 5 and 40 days, volatile solid concentrations (Sto) between 20 and 100 kg VS/m3, and temperatures between 15 and 52°C. The results indicated a maximum methane yield of 0.35 m3 (STP)/kg VS added at θ 30 days and Sto 20 kg VS/m3. Under such conditions, the energy conversion of the algal biomass to methane was 59%. The maximum methane production rate of 0.80 m3 (STP)/m3 day was obtained with θ= 20 days and S = 100 kg VS/m3. The mesophilic condition at 35°C produced the maximum methane yield and production rate. The process was stable and characterized by a high production of volatile acids (up to 23, 200 mg/L), alkalinity (up to 20, 000 mg/L), and ammonia (up to 7000 mg/L), and the high protein content of the biomass produced a well buffered environment which reduced inhibitory effects. At higher loading rates, the inhibition of methanogenic bacteria was observed, but there was no clear‐cut evidence that such a phenomenon was due to nonionized volatile acids or gaseous ammonia. The kinetic analysis using the model proposed by Chen and Hashimoto indicated that the minimum retention time was seven days. The optimum retention time increased gradually from 11 to 16 days with an increase in the initial volatile solid concentration. The kinetic constant K decreased with the improvement in the digester performance and increased in parallel with the ammonia concentration in the culture media.
Purification, characterization, and synergistic action of endoglucanases from Fusarium lini
Authors: Rao Mala , Deshpande Vasanti , Mishra Chitra 
Published: May 2005

AbstractFive endoglucanases (1,4‐β‐D‐glucan‐glucanohydrolase, EC 3.2.1.4) were isolated from Fusarium lini. Endo I and II were purified by preparative gel electrophoresis and Endo III, IV, and V were purified in a single‐step procedure involving preparative flat‐bed isoelectric focusing. All the endoglucanases were homogenous on disk gel electrophoresis and analytical isoelectric focusing in polyacrylamide gel. The pi values were between 6 and 6.6 for Endo III, IV, and V; for Endo I, the pi value was 8. The molecular weights of the enzymes were between 4 × 104 and 6.5 × 104. The Km values for endoglucanases using carboxymethyl cellulose (CM‐cellulose) as the substrate were 2–12 mg/mL. The specificity of the enzymes was restricted to β‐1, 4‐linkages. All the enzymes showed activity towards D‐xylan. The endoglucanases had high viscosity reducing activity with CM‐cellulose. Striking synergism was observed for the hydrolysis of CM‐cellulose by endoglucanases. Endo II, IV, and V attacked cellopentaose and cellotetraose more readily than cellotriose. Endo II and V hydrolyzed cellotriose, cellotetraose, and cellopentaose, yielding a mixture of cellobiose with a trace amount of glucose; endo IV produced only cellobiose.
Atypical kinetics of immobilized firefly luciferase
Authors: Blum Loïc J. , Coulet Pierre R. 
Published: May 2005

AbstractThe kinetic properties of collagen‐bound firefly luciferase have been investigated. Under definite hydrodynamic conditions with low agitation in the reaction medium, the observed behavior is modified compared to the enzyme free in solution: reducing the stirring rate decreases the observed enzymatic activity. But diffusional resistances alone cannot account for these atypical kinetics though mass transfer may certainly play an important role during the transient state of the bioluminescent reaction. After immobilization, the time necessary to reach the steady state increased from 300 ms to 3 min and the two substrates, luciferin and ATP, behave differently with respect to the enzyme: The nature of the saturating substrate first in contact with the bound enzyme is not indifferent suggesting that immobilization can reveal behaviors or mechanisms which are not visualized with the free enzyme.
Quantification of bacterial chemotaxis by measurement of model parameters using the capillary assay
Authors: Rivero‐Hudec Mercedes , Lauffenburger Douglas A. 
Published: May 2005

AbstractThe capillary assay for quantitative characterization of bacterial motility and chemotaxis is analyzed in terms of a mathematical model for cell population migration, in order to determine values for the cell random motility coefficient, μ and the cell chemotaxis coefficient, χ. The analysis involves both analytical perturbation methods and numerical finite‐difference techniques. Transient cell density profiles within the capillary tube are determined as they depend upon μ and χ, providing a means for estimating μ and χ from the common protocol measurements of cell accumulation in the tube at specified observation times. The effects of extraneous factors such as assay geometry, stimulus diffusivity, bacterial density, and observation time are thus separated from the intrinsic cell–stimulus interaction and response. This allows independent population measurements of cell chemosensory movement properties to be extrapolated to situations involving growth and competition of populations, for purposes of better understanding microbial population dynamics in systems of biotechnological and microbial ecological importance.
Validity of quasi‐steady‐state and transfer‐function representations for input–output relation in a Michaelis–Menten reaction
Authors: Sakamoto Naoto 
Published: May 2005

AbstractIn relation to the input–output characteristics of enzymatic reactions in the cellular metabolism and biochemical reactors, the validity of the quasi‐steady‐state and transfer‐function representations of reaction velocity has been examined for a basic Michaelis–Menten reaction employing computer simulation, that is, numerical integration of the rate equation. The well‐known S–v relationship (relationship between substrate concentration and reaction velocity)derived on the quasi‐steady‐state assumption is found to be in general a good approximation to the actual velocity throughout the temporal progress of the reaction. The validity of the approximation depends on a ratio of the Michaelis constant to the total enzyme concentration in the reaction system rather than on the individual rate constants. A transfer‐function representation is derived on assuming an exponential change in the reaction velocity for the indicial response to the substrate influx rate. The representation has a wider valid region with a decrease in influx rate than with an increase in the influx rate. The validity is most dependent on a ratio of total enzyme concentration to the steady‐state concentration of the substrate. The analysis of the linear sensitivity of the reaction velocity to rate constants reveals that the characteristics of these valid representations in systems analysis change according to the phase of the reaction.
Modulation by a high citrate concentration of kinetic parameters and of functional stability of two immobilized thylakoid systems
Authors: Thomasset Brigitte , Friboulet Alain , Barbotin Jean‐Noel , Thomas Daniel 
Published: May 2005

AbstractThis article deals with aspects of the reciprocal interaction between the activity of chloroplast membranes and their microenvironment. The artificial matrices used in the present work to immobilize thylakoids (albumin–glutaraldehyde matrix, polyurethane foam) can be regarded as weak ion exchangers. Thus, the distribution of the solute between the matrix surface and the external solution should, at least in part, be governed by a Donnan equilibrium. The influence of a high ionic strength medium (750mM potassium citrate) on the kinetic parameters (Kp1 Vm) and on the stability of the photosynthetic activity of immobilized chloroplast membranes has been studied. The results show similarities in behavior of the two supports studied in that, for both, a high concentration of salt (citrate) increases the apparent affinity for ferricyanide and allows a better transformation of this electron acceptor in CSTR experiments.
Mechanized systems for media dispensing, inoculation, and replication of microorganisms
Authors: Stieglitz B. , DeFelice C. P. 
Published: May 2005

AbstractTwo instruments were developed to mechanize the handling of anaerobic microorganisms for microbial mutant isolation. The instruments automatically dispense liquid or agar medium to large and small 96‐well platesand petridishes. Protocols were developed for inoculating different microorganisms, and calibration curves of number of areas or wells inoculated versus cell concentration were prepared for bacteria, yeast and fungi (spores). Experiments with yeast auxotrophic mutants and fungal spores showed that microbe inoculation follows Poisson statistics in distributing a single microorganism per inoculation point. The isolation and identification of Yarrowia lipolytica auxotrophic, morphological, and temperature‐sensitive or tolerant mutants demonstrated the use of the instruments for microbial screening.
Continuous hydrolysis of tallow with immobilized lipase in a microporous membrane
Authors: Taylor Frank , Panzer Curtis C. , Craig James C. , O'Brien Dennis J. 
Published: May 2005

AbstractThermostable lipase from Thermomyces lanuginosus was immobilized in untreated microporous membranes. Melted tallow pumped through the membrane did not wash the enzyme out. From 0.4 to 0.9% of the soluble activity remained after immobilization with half‐lives of 1–2 months or more at 50°C. Membranes can be acid/base washed and reloaded with enzyme with no adverse effects. Buffer was required for a long half‐life, and recycling the buffer improved the mass transfer of glycerol out of the immobilized lipase reactor. Immobilized activity was unaffected when the pH of the aqueous product changed from 5.5 to 6.5.
Feedback identification of continuous microbial growth systems
Authors: O'Neil D. G. , Lyberatos G. 
Published: May 2005

AbstractThe fundamental problem of dynamic modeling of continuous culture systems for process control and optimization is addressed. Forcing a system to bifurcation via feedback control is a very promising method for model discrimination and identification. Dynamic information is obtained by using this technique, the dynamic behavior of the chemostat as predicted by unstructured models, the model with delay, and a structured model has been analyzed. The method exposes significant differences in the nonlinear dynamic structure of the various models and can be implemented to discriminate between various possible models for a continuous culture system.
Systems analysis of the culture physiology in acetone–butanol fermentation
Authors: Yerushalmi L. , Volesky B. , Votruba J. 
Published: May 2005

AbstractThe Pronounced differences in performance of a strain of Clostridium acetobutylicum ATCC 824 were analyzed by the method of systems analysis. The mechanism for cellular transport of substrate (glucose), solvents, and acids was studied and mathematically formulated. The systems analysis approach in the treatment of data from culture experiments pointed out the cell membrane malfunction indicated by its altered permeability and reflected in the altered number of active sugar transport sites. Experimental results obtained from the study of the cell uptake of 3‐0‐methyl glucose (0.7mM) by the “normal culture” and the “retarded culture” confirmed the theoretical predictions regarding a slower transport in the retarded culture. The initial uptake rate and the accumulation coefficient of the sugar in the normal culture were 15.0 and 4.1 times higher, respectively, than those for the retardedculture. Adjustment of the culture pH resulted in further increases in these parameters by factors of 3.0 and 3.5, respectively.
Cadmium accumulation by immobilized cells of a Citrobacter sp. using various phosphate donors
Authors: Michel L. J. , Macaskie L. E. , Dean A. C. R. 
Published: May 2005

AbstractImmobilized cells of a Citrobacter species scavenge cadmium with high efficiency from challenge flows containing Cd2+. Metal uptake by the cells in mediated by a cellbound phosphatase which liberates inorganic phosphate from an organic phosphate to precipitate cadmium as cell‐bound metal phosphate. Hitherto glycerol 2‐phosphate has served as the phosphate donor, but for an economic large scale process an inexpensive and readily available phosphate donor is required and the use of alkyl phosphates was investigated. This was limited due to interference by the alcohol simultaneously liberated. An alternative, pulsed process is described whereby alkyl phosphate‐supplemented main pulses interspersed with short alkyl phosphate‐free “recovery” pulses greatly reduced the requirement for glycerol 2‐phosphate. Wider aspects of phosphate donor utilization were also investigated to compare this strain of Citrobacter with a strain previously reported to accumulate lead but not cadmium.
Synthesis and regulation of extracellular β (1–3) glucanase and protease by cytophaga sp. In batch and continuous culture
Authors: Andrews B. A. , Asenjo J. A. 
Published: May 2005

AbstractLytic enzyme systems with the ability to break whole cells of yeast are a mixture of several enzymes and virtually all contain β(1–3)glucanases and some protease. It appears that the presence of these two enzyme activities is necessary to break the two layers of the rigid cell wall. The enzyme system of Cytophaga NCIB 9497 has a high activity towards the walls of yeast and also of bacteria. This article describes the production of this extracellular lytic enzyme system in batch and continuous culture—it was found to be inducible. The synthesis and regulation of the two main constituent enzymes, β(1–3)glucanase and protease, have been investigated. The synthesis of β(1–3)glucanase is regulated by bothinduction (by an unknown inducer) and catabolite repression. Highβ(1–3)glucanase activities were obtained in continuous culture at low dilution rates over a narrow range (0.05–0.10 h−1), and there is evidence of the presence of more than one glucanase enzyme. Proteolytic activity appears subject to catabolite repression and made up of the activities of more than one protease enzyme. Productivity and enzyme concentration were increased several fold in continuous culture when compared to batch culture.
Computational algorithms for optimal feed rates for a class of fed‐batch fermentation: Numerical results for penicillin and cell mass production
Authors: Lim H. C. , Tayeb Y. J. , Modak J. M. , Bonte P. 
Published: May 2005

AbstractBased upon the general characteristics of the optimal feed rate profiles presented in an earlier article, efficient computational algorithms have been developed for fed‐batch fermentation processes described by four or less mass balance equations. These algorithms make computations of optimal substrate feed rate profiles straight forward and simple for various fed‐batch cultures for such products as antibiotics, amino acids, enzymes, alcohols, and cell mass. Numerical examples of penicillin fermentation and bacterial cell mass production are given in detail, illustrating the use of these algorithms.