bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cybernetic modeling of microbial growth on multiple substrates
Authors: Kompala Dhinakar S. , Ramkrishna Doraiswami , Tsao George T. 
Published: December 2004

AbstractThe internal regulatory processes, which underlie a variety of behavior in microbial growth on multiple substrates, are viewed as a manifestation of an invariant strategy to optimize some goal of the cells. A goal‐seeking or cybernetic model is proposed here, with the optimization obased on a short‐term perspective of response to the environment. The model parameters are determined from the growth data on single substrates. The model predicts the entire range of microbial growth behavior on multiple substrates from simultaneous utilization of all sugars to sequential utilization with pronounced diauxic lags. It is shown to predict the many variations of the diauxic phenomenon in different growth conditions. The transients in continuous culture growth on mixed substrates caused by varying the feed strategies are easily simulated by this model. The framework of this model can be applied to batch or continuous culture growth of many bacteria on different combinations of substrates.
Thermal stabilization of amylolytic enzymes by covalent coupling to soluble polysaccharides
Authors: Lenders J.‐P. , Crichton R. R. 
Published: December 2004

AbstractThe immobilization of pullulanase and β‐amylase on soluble polysaccharides (dextrans and amylose) has been carried out. The method used for coupling the enzymes to the carbohydrate support involves limited periodate oxidation of the polysaccharide followed by reductive alkylation with sodium cyanoborohydride or borohydride. The influence of the degree of functionalization of the carbohydrate, the incubation time, the nature of the reducing agent and, for the dextrans studied, their molecular weight, on the properties of the conjugate were studied. We have observed an apparent correlation between the molecular weight of the glycoprotein conjugates formed and their thermal stability, resistance to urea denaturation and their kinetic parameters. By selecting the proper experimental conditions leading to conjugates with maximum thermal stabilities, it has also been shown that β‐amylase conjugates can hydrolyze starch at a temperature 20°C higher than the corresponding value for the native enzyme. This result demonstrates that conjugation may result in modified enzymes leaving a high operational stability at elevated temperatures. We suggest that the immobilization method presented in this article represents an approach to the stabilization of enzymes employed at an industrial level, which may be of general application.
A cybernetic view of microbial growth: Modeling of cells as optimal strategists
Authors: Dhurjati P. , Ramkrishna D. , Flickinger M. C. , Tsao G. T. 
Published: December 2004

AbstractA cybernetic framework is presented which views microbial response in multiple substrate environments as a judicious investment of cellular resources in synthesizing different key proteins according to an optimal regulatory strategy. A mathematical model is developed within the cybernetic framework for the diauxic growth of Klebsiella pneumoniae on a mixture of D‐glucose and D‐xylose. The “bang–bang” optimal policy describes well the experimental observations obtained using a fermenter coupled to an Apple II microcomputer. Striking variations in respiratory levels are observed experimentally during the switching of the cell's adaptive machinery for the utilization of the less preferred substrate.
Solid‐state fermentation of sweet sorghum to ethanol
Authors: Kargi Fikret , Curme James A. , Sheehan John J. 
Published: December 2004

AbstractSolid‐state fermentation of chopped sweet sorghum particles to ethanol was studied in static flasks using an ethanol tolerant yeast strain. The influence of various process parameters, such as temperature, yeast cell concentration, and moisture content, on the rate and extent of ethanol fermentation was investigated. Optimal values of these parameters were found to be 35°C, 7 × 108 cells/g raw sorghum, and 70% moisture level, respectively.
Enzymatic gallic acid esterification
Authors: Weetal Howard H. 
Published: December 2004

AbstractGallic acid esters of n‐propyl and amyl alcohols have been produced by enzymatic synthesis in organic solvents using immobilized tannase. Studies indicate that maximum esterification of gallic acid occurs with amyl alcohol. The enzyme shows broad alcohol specificity. However, the enzyme exhibits absolute specificity for the acid portion of the ester. Studies were carried out on Km, Vmax, pH, and temperature optima.
Enzymatic hydrolysis and recrystallization behavior of initially amorphous cellulose
Authors: Bertran Maria Silvia , Dale Bruce E. 
Published: December 2004

AbstractCellulose samples from cotton and wood pulps with varying low degrees of crystallinity (mechanically decrystallized) were studied. The influence of initial cellulose crystallinity on sugar yield after enzymatic hydrolysis was determined by two different methods. As expected, samples with low crystallinity were much more accessible to enzymatic attack and glucose yields were higher than were samples of high initial crystallinity. Hydrolysis of cellulose seems more dependent on cellulose crystallinity than on the source of cellulose. It is known that decrystallized or amorphous cellulose can recrystallize under proper conditions, e.g., during acid hydrolysis. The data reported here also reveal some recrystallization during enzymatic hydrolysis which probably occurs simulataneously with a selective enzymatic attack on the amorphous regions of cellulose. In all cases, the amorphous celluloses recrystallized in the original lattice form, that of native cellulose.
Application of the upflow anaerobic sludge bed (UASB) process for treatment of complex wastewaters at low temperatures
Authors: Koster I. W. , Lettinga G. 
Published: December 2004

AbstractThe feasibility of the upflow anaerobic sludge bed (UASB) process for the treatment of potato starch wastewater at low ambient temperatures was demonstrated by operating two 5.65‐L reactors at 14°C and 20°C, respectively. The organic space loading rates achieved in these laboratory‐scale reactors were 3 kg COD/m3/day at 14°C and 4‐5 kg COD/m3/day at 20°C. The corresponding sludge loading rates were 0.12 kg COD/kg VSS/day at 14°C and 0.16−0.18 kg COD/kg VSS/day at 20°C.These findings are of considerable practical importance because application of anaerobic treatment at low ambient temperatures will lead to considerable savings in energy needed for operating the process. As compared with various other anaerobic wastewater treatment processes, a granular sludge upflow process represents one of the best options developed so far. Although the overall sludge yield under psychrophilic conditions is slightly higher than under optimal mesophilic conditions, this doesn't seriously hamper the operation of the process. The extra sludge yield, due to accumulation of slowly hydrolyzing substrate ingredients, was 4.75% of the COD input at 14°C and 1.22% of the COD input at 20°C.
Feasible and optimal retrofitting of batch‐soluble to continuous‐immobilized enzyme processes applied to adsorbed enzymes
Authors: Domach M. M. , Gricus T. J. 
Published: December 2004

AbstractThe advantages of retrofitting an in situ soluble enzyme batch process to an immobilized enzyme continuous process are contrasted against the disadvantages by means of a dimensionless feasibility/optimization analysis. The general analysis is applied to the case of an adsorbed enzyme system where a maximum in activity occurs with respect to loading. For this case, a minimum in the ratio of enzyme‐carrier complex working lifetime to in situ batch process time and a maximum in the cost difference between the in situ and retrofit processes occurs with respect to loading and retrofit process conversion. For the maximization of cost difference, the analysis also suggests a criterion that can be used to determine whether the values for optimal loading and retrofit conversion will result in the retrofit being economically feasible. When infeasibility occurs, qualitative sensitivity analysis for a variety of situations points out whether a catalyst or process modification will improve feasibility the most. Apart from forming the basis for an iterative retrofit process design algorithm, the modeling approach's ability to specify optimal values of catalyst properties such as loading lends itself to defining process‐specific, catalyst design “targets” would be useful for those developing immobilized enzyme preparation methodology and those investigating enzyme–carrier interactions.
Structure and properties of enzyme graft copolymers: Temperature effects on HRP immobilization mechanism
Authors: D'Angiuro L. , de Lalla C. , Cremonesi P. 
Published: December 2004

AbstractThe possibility of obtaining immobilized horseradish peroxidase (HRP) materials with K′m values close to that of the native enzyme, but with good thermal stability, was investigated. The photochemical reaction was used as the immobilization methodology. Temperature and catalyst concentration were found to be the main parameters able to control the immobilization reaction mechanism more than type of functional monomer, polymer–matrix, and enzyme–polymer ratios. By carrying out the immobilization reaction at 35°C and using either bisacryloylpiperazine (BAP) or hexhydro‐1,3,5‐triacryloyl‐s‐triazine (HTsT) as the functional monomer, materials with a good thermal stabilization (the retained activity after 240 min at 60°C was between 65–25%) as well as kinetic constants (0.6–0.8 × 10−4M) similar to that of the free enzyme (0.57 × 10−4M) were obtained. Since low K′m values were obtained also using a high polymer content (pBAP copolymers, 25%; pHTsT copolymers, 30%) and neither limitation to substrate diffusion nor a reduction of the enzyme mobility was found, the enzyme should be linked to the matrix during the last steps of monomer polymerization, and it should have an external disposition with respect to the support.
Heterogeneous denaturation of enzymes: A distributed activation energy model with nonuniform activities
Authors: Agarwal Pradeep Kumar 
Published: December 2004

AbstractA model is proposed for the denaturation of enzymes based on heterogeneous enzyme subpopulations with nonuniform initial activities and nonzero final activities. The more frequently used simple first‐order deactivation model is a special case of the model corresponding to the standard deviation of Gaussian distribution of activation energies approaching zero. Parametric studies made with the model are capable of simulating the reported trends in experimental data on the thermal profile and activity time behavior of native as well as modified enzymes with a minimum number of adjustable parameters. The model predictions are found to be in good agreement with data reported in the literature.
Steric hindrance of growth of filamentous fungi in solid substrate fermentation of wheat straw
Authors: Laukevics J. J. , Apsite A. F. , Viesturs U. S. , Tengerdy R. P. 
Published: December 2004

AbstractCellulolytic fungi, such as Trichoderma reesei, T. lignorum, and Chaetomium cellulolyticum reach a low packing density of mycelia when grown on straw under conditions of solid substrate fermentation. The low packing density is shown to be caused partially by the geometric limitation of the growth of mycelia in the substrate and particularly in its pores, but the exact contribution of this limitation and other limitations such as mass transfer and substrate availability cannot be easily distinguished. The combined effect of such limitations is called steric hindrance. This steric hindrance is associated with and may be the principal cause of low biomass concentration in SSF.
Ion exchange process for removing glucosyltransferase from crude glucoamylase
Authors: Ayers J. S. 
Published: December 2004

AbstractThe advant of a new range of high‐protein capacity cellulosic ion exchangers suitable for use on an industrial scale made it worthwhile investigating the conditions necessary to remove the contaminating enzyme glucosyltransferase from a commercial preparation of crude glucoamylase. The potential of the SP derivative, SP Indion®, for achieving this separation is shown. At pH 2.5 the glucosyltransferase was selectively adsorbed by the ion exchanger, and 99% of the glucoamylase was recovered in the eluate from the column. Purification of an Aspergillus culture filtrate by this method will require careful control of the ionic strength of the culture medium if it is to be used without the additional step of cation exchange to lower than pH to 2.5.
Stability of alginate‐immobilized algal cells
Authors: Dainty A. L. , Goulding K. H. , Robinson P. K. , Simpkins I. , Trevan M. D. 
Published: December 2004

AbstractInvestigations were carried out using immobilized Chlorella cells to determine the diameter, compressibility, tolerance to phosphate chelation, and ability to retain algal cells during incubation of various alginate beads. These physical bead characteristics were found to be affected by a variety of interactive factors, including multivalent cation type (hardening agent) and cell, cation, and alginate concentration, the latter exhibiting a predominant influence. The susceptibility of alginate beads to phosphate chelation was found to involve a complex interaction of cation type, concentration, and pH of phosphate solution. A scale of response ranging from gel swelling to gel shrinking was observed for a range of conditions. However, stable calcium alginate beads were maintained in incubation media with a pH of 5.5 and a phosphate concentration of 5μM. A preliminary investigation into cell leakage from the beads illustrated the importance of maintaining a stable gel structure and limiting cell growth to reduce leakage.
Dilute acid hydrolysis of wheat straw hemicellulose at moderate temperature: A simplified kinetic model
Authors: González G. , López‐Santín J. , Caminal G. , Solà C. 
Published: December 2004

AbstractWheat straw has been hydrolized with sulfuric acid at 34 and 90°C. The treatment at 90°C yields complete solubilization of hemicellulose to xylose and arabinose without significant amounts of furfural. The influence of acid concentration was studied and the kinetics of the acid‐catalyzed hydrolysis has been modeled suggesting a two‐consecutive reactions mechanism. This model is useful to explain the different behavior of the concentration of the two main sugars produced. The enhanced cellulose accessibility to enzymatic attack is also reported.
Growth of animal cells on microbeads. I. In situ estimation of numbers
Authors: Miller S. J. O. , Henrotte M. , Miller A. O. A. 
Published: December 2004

AbstractEvaluation of the number of anchorage‐dependent cells growing on the surface of microbeads kept in suspension in a bioreactor is a tedious procedure fraught with many difficulties. Using the Coulter counter as a biomass probe, this article shows that the number of cells adhering to microbeads can be determined while the cells are still attached.
Role of exocellular polymer in the design of activated sludge
Authors: Sheintuch M. , Lev O. , Einav P. , Rubin E. 
Published: December 2004

AbstractThis research is aimed at understanding the reactor‐settler interaction. The reactor operating conditions affect the sludge‐settling properties due to (a) production of exocellular polymer that serves as a flocculant in the settler and (b) population shift from flocculating bacteria to filamentous microorganisms that do not settle. A structured kinetic model that accounts for stored substrate and production of polymers, biomass, and inerts was constructed and applied to various open and closed reactor configurations. It is based on our observation that, in a batch reactor, the polymer is produced during endogenous respiration. The model describes well the observed temporal variation in substrate, biomass, and polymer concentration. Application of the model to continuous operation predicts increasing polymer concentration with sludge age, which is in good agreement with one study in the literature. Our study in a once‐through reactor, as well as others, suggests an inverse dependence. The difference is probably due to different operating modes. Our study confirmed the role of the polymer in the sedimentation process. Under some conditions, however, a slow population shift to filamentous growth becomes the dominant factor.
Encapsulation of viable cells within polyacrylate membranes
Authors: Gharapetian H. , Davies N. A. , Sun A. M. 
Published: December 2004

AbstractA new, semipermeable hydrogel membrane for encapsulating viable cells has been developed. The encapsulation was performed by consecutively introducing droplets of a suspension of hybridoma cells in a solution of a polyanionic acrylic copolymer into aqueous solutions of three polycationic polymers. As a result of interpolymeric ionic interactions and some chemical reactions, a polyelectrolyte complex membrane was formed at the interface between each droplet and the polycationic polymeric solutions. The hybridoma cells, used as a model system, were derived by fusing spleen cells from immunized BALB/c mice with the NS‐1 murine plasmacytoma cell line. The cells divided and gradually filled the microcapsules over a period of 8 days. Prior to encapsulation of the hybridoma cells, the polyanions were tested for toxicity and inhibition of cell growth. A direct relationship was observed between hybridoma cell viability in the acrylic polyanion/RPMI‐1640/10% (w/v) fetal calf serum (FCS) solutions and the kinematic viscosities of the solutions of the polyanions. Antihuman IgM was produced by the encapsulated hybridoma cells and immunoassay showed that the antibody concentration was 3 μg/ml of the total culture medium.
Quantitative method based on energy and mass balance for estimating substrate transient accumulation in activated sludge during wastewater treatment
Authors: Guiot S. R. , Nyns E. J. 
Published: December 2004

AbstractTo calculate the transient accumulation of soluble organic matter in activated sludge, an equation based on COD and respirometry is described. In this approach the difference between the actual utilized organic matter and the metabolized matter is expressed as substrate transient accumulation. The amount of substrate generated by the lysis of dead microorganisms was taken into account, and the metabolized organic matter was expressed in two main endergonic functions of O2 consumption, that is, assimilation and maintenance. The equation thus derived was simplified to contain parameters such as COD and O2 consumption and tested on experimental results. The results show that the values obtained using this equation compared well to substrate removal in the absence of O2 in short‐term batch cultures.
Mechanistically detailed model of cellular metabolism for glucose‐limited growth of Escherichia coli B/r‐A
Authors: Peretti Steven W. , Bailey James E. 
Published: December 2004

AbstractA structured mathematical model for cellular metabolism in Escherichia coli has been extended to encompass the mechanistic structure surrounding the kinetics and control of transcription and translation. The dependence of transcription on RNA polymerase and the mechanism of translation initiation have been explicitly included. This model correctly simulates cell growth, cell composition, and the timing of chromosome synthesis as a function of extracellular substrate concentration for glucose‐limited balanced growth. Simulation results for the subpopulation of RNA polymerase engaged in transcription and for the distribution of this subpopulation among different promoter sites agree closely with experimental findings, as do calculated estimates of the active ribosomal fraction. In addition, the existence of an antitermination system for transcription of stable RNA operons is supported by model results. This model should provide a useful framework for investigating metabolic perturbations to E. coli, such as those resulting from insertion of extra‐chromosomal vectors into the cells.
Enhancement of enzymatic hydrolysis of cellulose by surfactant
Authors: Ooshima Hiroshi , Sakata Masaru , Harano Yoshio 
Published: December 2004

AbstractEffects of surfactants on enzymatic saccharification of cellulose have been studied. Nonionic, amphoteric, and cationic surfactants enhanced the saccharification, while anionic surfactant did not. Cationic and anionic surfactants denatured cellulase in their relatively low concentrations, namely, more than 0.008 and 0.001%, respectively. Using nonionic surfactant Tween 20, which is most effective to the enhancement (e.g., the fractional conversion attained by 72 h saccharification of 5 wt % Avicel in the presence of 0.05 wt % Tween 20 is increased by 35%), actions of surfactant have been examined. As the results, it was suggested that Tween 20 plays an important role in the hydrolysis of crystalline cellulose and that Tween 20 disturbs the adsorption of endoglucanase on cellulose, i.e., varies the adsorption balance of endo‐ and exoglucanase, resulting in enhancing the reaction. The influence of Tween 20 to the saccharification was found to remain in simultaneous saccharification and fermentation of Avicel.
Coexistence of S. cerevisiae and E. coli in chemostat under substrate competition and product inhibition
Authors: Davison Brian H. , Stephanopoulos Gregory 
Published: December 2004

AbstractA mixed culture of Saccharomyces cerevisiae and Escherichia coli was established in a stable coexistence steady state in a chemostat under constant operating conditions. The species competed for glucose, the growth‐limiting resource, and produced acetate and ethanol. The acetic acid was shown to be very inhibitory to E. coli in pure culture at pH 5 while ethanol inhibition was only marginal. No significant inhibition of S. cerevisiae growth was observed by either acetate or ethanol. Pure culture parameters were measured and used in the analysis. Linearized stability analysis for the case when both organisms produce the inhibitor showed that a transition through three stable outcomes was possible as the feed concentration is lowered. Experimental studies verified these predictions, and successive transitions from a yeast growth steady state, to a coexistence steady state, and to an E. coli growth steady state were obtained by lowering the glucose concentration in the feed from 10 to 5 to 2.5 g/L, respectively. This dynamic behavior is distinct from the outcomes of other competition–inhibition combinations and experimentally demonstrates for the first time that coexistence is possible due to substrate competition and product inhibition.
Properties of cellulase immobilized on agarose gel with spacer
Authors: Chim‐anage Patoomporm , Kashiwagi Yutaka , Magae Yumi , Ohta Teruo , Sasaki Takashi 
Published: December 2004

AbstractCellulase produced by fungus Trichoderma viride was immobilized on agarose beads (Sepharose 4B) activated by cyanogen bromide and also on activated agarose beads that contained spacer arm (activated CH‐Sepharose 4B and Affi‐Gel 15). The CMCase activity retained by immobilized cellulase on activated Sepharose containing the spacer tended to be higher than that immobilized without spacer, although the extent of protein immobilization was lower. Also, the higher substrate specificity for cellulase immobilized on beads with spacer was obtained for cellobiose, acid‐swollen cellulose, or cellulose powder. The hydrolysis product from their substrates was mainly glucose.