bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of sludge flocs on the aeration performance of suction‐impellers
Authors: van der Kroon Gerard T. M. , Vlot Jaap
Published: May 2005

The authors have investigated a special aspect of the transfer of oxygen: the aeration performance of small‐scale suction‐impellers in a suspension of activated sludge floes and a performance comparison with clear water. The principle of the impellers is, that in order to disperse air bubbles into the aforementioned liquids, all that we need do is a simple stirring. Due to the impellers the authors could not show a reduction of the oxygen transfer coefficient in the presence of sludge flocs. Former comparative studies of oxygen transfer, using a fixed orifice, did show a reduction in the presence of sludge flocs. Therefore, it seems probable that the effect of activated sludge flocs on the transfer coefficient is linked with the manner in which air is dispersed, i.e., depends on whether an orifice is fixed or moved. The experimental results allow presumption that by developing a high intensity of shear near the location where air bubbles are produced, we are able to minimize the effect of sludge flocs on the process of bubble formation.
Improved medium for saprophytic production of ergot alkaloids by Claviceps purpurea (Fr.) Tul.
Authors: Sambamurthy K. , Rao L. Nageshwara
Published: May 2005

Studies were undertaken on the production of ergot alkaloids in saprophytic culture employing two strains of C. purpurea. In an attempt to improve the yield of the alkaloids and to develop a cheaper medium, the commonly used carbohydrate source, mannitol, was replaced with different types of starches and starchy materials as these are comparatively much cheaper than mannitol. Results indicated that, in stationary cultures, certain starches enhanced the yield greatly, while in shaker cultures starches could replace mannitol for equivalent yields.
A generalization of kinetic data on sulphite oxidation systems
Authors: Linek V. , Tvrdík J.
Published: May 2005

Kinetic data of the reaction between sulphite ions and dissolved oxygen depend on the purity of sulphite used. Thus it is adequate to determine them for each batch and concentration of sulphite used. Besides the dependence of reaction rate constants on catalyst concentration, it is usually also required to know their dependence on pH and on temperature. Both quantities can change to a great extent especially in absorption apparatus in which high sulphite conversion occurs. They profoundly influence the value of the reaction rate constant. To get a complete picture of the influence of these three quantities without repeating extensive kinetic measurements for every kind and concentration of sulphite used, a method for obtaining information on the influence of all three quoted quantities in the range of values of interest for application is presented.
Effect of shear on the death of two strains of mammalian tissue cells
Authors: Augenstein D. C. , Sinskey A. J. , Wang D. I. C.
Published: May 2005

This study reports some findings on the death of mammalian cells occurring from fluid dynamic effects when they are pumped through capillaries. The cell strains used were human HeLa S3 and mouse L929, grown in monolayer culture. Cells were harvested and suspensions were pumped through various lengths and diameters of stainless steel capillary tubing. Viability of the cells was assayed by the dye exclusion test. Cell deaths occurred and could be correlated with either average wall shear or power dissipation within the capillary tube. L929 cells were found to be more sensitive than HeLa S3 cells at all shear rates tested.
Oxygen transfer and scale‐up in lysine production by Ustilago maydis mutant
Authors: Sanchez‐Marroquin A. , Ledezma M. , Barreiro J.
Published: May 2005

The oxygen transfer coefficient estimated by both sulfite and dynamic methods and some of the rheological properties of fermentation broths derived from the batch cultivation of a mutant of U. maydis in a sugar cane juice substrate, are used in a scaling‐up procedure on the basis of the power consumption per volume unit concept. The fluid was of the Binham plastic type; the Np‐NRE correlations showed that the modified Reynolds numbers of the flat‐blade turbine impellers were low, near to or in the laminar region; the Na‐Pg/P relations were established and then used in the calculation regardless of the geometrical dissimilarities of the vessels. A change of scale from 5 to 50 liters was calculated and operated keeping the power per volume value constant. Reproduction of lysine yields, 2.5–3.2 g/liter, was repeatedly reached in 8 successive runs.
Simulation of oxygen transfer in microbial slimes
Authors: Bungay H. R. , Harold D. M.
Published: May 2005

A model based on diffusion mechanisms accounts for oxygen transfer from flowing nutrient medium into a film of organisms in slime. Profiles of dissolved oxygen concentration are generated at distances downstream from the start of the slime. In these studies, the nutrient medium was assumed rich, thus the rate of oxygen transport limited microbial respiration. Parameter sensitivity tests were performed for flow rate, oxygen concentration in the medium, and mass transfer coefficients.
Kinetic modeling of the hydrolysis of sucrose by invertase
Authors: Bowski L. , Saini R. , Ryu D. Y. , Vieth W. R.
Published: May 2005

The kinetics of the enzymatic hydrolysis of sucrose by invertase have been examined, with particular emphasis on high substrate concentration. Initial rates of reaction were determined by following the production of glucose directly as a function of time over a wide range of substrate concentrations (0.04M to 2.06M). The resulting data reveal a reaction rate that increases gradually until the sucrose concentration reaches about 0.29M, after which the reaction velocity decreases with increasing sucrose concentration. Previous workers (e.g., Nelson and Schubert1) have reported a peak reaction velocity as determined by indirect polarimetric measurements of glucose, at a sucrose concentration of about 0.17M. These measurements, however, neglect the intermediate oligosaccharides formed by the transferase action of invertase,8–10 and assume equal amounts of glucose and fructose. According to Anderson et al.,10 these oligosaccharides interfere by producing an erroneously low reaction rate. Experimental results of this work confirm Anderson's observations, and show a further reaction rate increase of nearly 20% between sucrose concentrations of 0.177M and 0.285M under the same conditions of temperature, pH, and enzyme‐concentration.

Effects of substrate diffusion, solution viscisity, water concentration, and substrate inhibition were experimentally studied and the results incorporated into a kinetic model that has proven satisfactory in modeling the experimental results. This model takes into account inhibition by primary substrate, with concentration of the secondary substrate water, as a rate limiting factor at sucrose concentrations greater than 0.285M.

The effects of the mixing, in terms of volumetric power input, on the relation rate have been tested. Approximately 40‐fold increase in volumetric power input caused on increase in the reaction rate. These experiments have shown that bulk mass transfer is not a rate limiting factor under the experimental conditions.
Hydrocarbon fermentations using Candida lipolytica. I: Basic growth parameters for batch and continuous culture conditions
Authors: Moo‐Young M. , Shimizu T. , Whitworth D. A.
Published: May 2005

Candida lipolytica (strain ATCC 8661) was grown on a simple defined medium with n‐dodecane as sole carbon source under batch and continuous fermentation conditions. The composition of cellular material recovered from the fermentations, the oxygen demand of the cells, and the effect of operating conditions on cell growth were evaluated experimentally. These basic data are presented and discussed.
Hydrocarbon fermentations using Candida lipolytica. II: A model for cell growth kinetics
Authors: Moo‐Young M. , Shimizu T.
Published: May 2005

A mechanistic model is presented for the growth kinetics of a yeast grown by submerged aerobic fermentation using a liquid hydrocarbon as sole carbon source. The model is based on the assumption that cell growth is governed by the extent of probable cell attachment at the hydrocarbon oil‐droplet surfaces in a four‐phase dispersion. An analytical expression has been developed for the model. It is shown that for the case of relatively small oil droplets, the model predicts the present and previous experimental data for growth of yeasts (Candida species) in n‐alkane systems. The model is further examined for maximal growth in terms of substrate dilution rate and agitation power consumption for a continuous fermentation process.
Growth of microbes in an oil‐continuous environment
Authors: Coty V. F. , Gorring R. L. , Heilweil I. J. , Leavitt R. I. , Srinivasan S.
Published: May 2005

The growth of microorganisms in fermentations where oil had been maintained as the continuous phase was examined to determine whether advantage could be gained from the increased solubility of oxygen in hydrocarbon. Although cell concentrations were highest in the aqueous phase of oil‐continuous systems, due to the large oil fraction, productivities achieved per unit fermenter volume were generally equivalent to those obtained from water‐continuous systems. With the oil‐continuous emulsions, the power requirement for aeration and mixing was less, and phase reversal resulted in a threefold concentration of cells in the aqueous medium, thereby facilitating their recovery.
A pilot plant apparatus for continuous phased culture—some observations on oxygen usage by Candida utilis during the cell cycle
Authors: Dawson P. S. S.
Published: May 2005

An inexpensive scale‐up of the cyclone column apparatus (Can. J. Microbiol., 11, 893 (1965)) is described which is suitable for pilot plant studies on the 10 liter scale. Details of its construction and operation are given.

Experimental with phased cultures of C. utilis growing in the equipment are reported during which studies of dissolved oxygen and oxygen uptake were made over the cell cycle. Changes in both oxygen parameters occurred during the cycle and were useful as monitors of the growth. Cell of C. utilis were found to be very sensitive to changes in oxygen supply during the early stages of the cell cycle.
Discussion on entrained droplets in fermenters used for the cultivation of single‐celled mircoorganisms
Authors: Hamer G.
Published: May 2005

The validity of regarding the liquid phase in vigorously agitated sparged fermenters during the cultivation of single‐celled aerobic microorganisms as essentially homogeneous is examined. Droplet formation from bursting bubbles and physical effects of the spray environment on single‐celled microorganisms are discussed. The implications of droplet removal from the head space of fermenters by collision with and drainage down the walls are considered, particularly factors concerned with wall growth above the liquid level in fermenters.
Parameter adaptation and control in a biochemical reactor
Authors: Weinrich S. D. , Lapidus L.
Published: May 2005

A discrete optimally sensitive controller is developed which yields steady‐state feedback control of a three‐stage biochemical reactor system in spite of system parameter variations. A feedback law is implemented that estimates those variations which cause the output states to deviate from nominal, and adjusts the control policy in light of these variations.
A kinetic model for microbial growth on solid hydrocarbons
Authors: Chakravarty M. , Amin P. M. , Singh H. D. , Baruah J. N. , Iyengar M. S.
Published: May 2005

A kinetic model has been presented to explain the growth of microorganism on solid hydrocarbons. The model is based on the assumption that metabolite produced by the growing cells helps the dissolution of the solid substrate in the aqueous medium. The linear behavior of the growth curve predicted by the model is verified experimentally.
Effect of mercury on algal growth rates
Authors: Hannan Patrick J. , Patouillet Constance
Published: May 2005

In experiments with one freshwater (Chlorella pyrenoidosa) and three marine organisms (Phaeodactylum tricornutum, Cyclotella nana, and Chaetoceros galvestonensis), mecury was more toxic than the other metals tested (silver, cadmium, lead, and copper); and its toxicity is comparatively irreversible. Growth was monitored by changes in fluorescence of the cultures over a 3‐day test period. The toxicity of the mercury varied inversely with the concentrations of nutrients present. Preliminary experiments indicate that mercury in the form of mercuric chloride is more than as dimethylmercury.
Continuous culture of Pseudomonas fluorescens with sodium maleate as a carbon source
Authors: Edwards Victor H. , Kinsella John E. , Sholiton David B.
Published: May 2005

Pseudomonas fluorescens (ATCC 11150) was grown in batch and continuous culture in minimal media with sodium maleate as growth‐limiting sole organic carbon source. Growth was followed by turbidity and dry weight measurements. Gross composition of washed cells (relative amounts of protein, lipid, RNA, and DNA) and the distribution of amino acids in protein hydrolyses of the cells were determined for cells grown in continuous culture at various dilution rates. Extracellular concentrations of the original carbon source and a number of metabolites were monitored by a total carbon analysis, ion exchange chromatography, and ultraviolet‐visible scans of cell‐free supernatants and chromatographic fractions, thereof.

Substrate inhibition by maleate was a major factor in the growth kinetics of both batch and continuous cultures. Excessive maleate concentration caused instability in continuous cultures. By appropriate operation, much higher specific growth rates (0.305/hr) could ultimately be achieved in continuous culture compared to batch culture (0.174/hr). Adaptation was responsible for only part of the differences between batch and continuous cultures; the differing distribution of metabolites were also major factors.
A radial flow hollow fiber bioreactor for the large‐scale culture of mammalian cells
Authors: Tharakan John P. , Chau Pao C.
Published: May 2005

A radial flow hollow fiber bioreactor has been developed that maximizes the utilization of fiber surface for cell growth while eliminating nutrient and metabolic gradients inherent in conventional hollow fiber cartridges. The reactor consists of a central flow distributor tube surrounded by an annular bed of hollow fibers. The central flow distributor tube ensures an axially uniform radial convective flow of nutrients across the fiber bed. Cells attach and proliferate on the outer surface of the fibers. The fibers are pretreated with polylysine to facilitate cell attachment and long‐term maintenance of tissuelike densities of cell mass. A mixture of air and CO2 is fed through the tube side of the hollow fibers, ensuring direct oxygenation of the cells and maintenance of pH. Spent medium diffuses across the cell layer into the tube side of the fibers and is convected away along with the spent gas stream. The bioreactor was run as a recycle reactor to permit maximum utilization of nutrient medium. A bioreactor with a membrane surface area of 1150 cm2 was developed and H1 cells were grown to a density of 7.3 × 106 cells/cm2.
Study of lignin biotransformation by Aspergillus fumigatus and white‐rot fungi using 14C‐labeled and unlabeled kraft lignins
Authors: Kadam Kiran L. , Drew Stephen W.
Published: May 2005

The biodegradation of lignin by fungi was studied in shake flasks using 14C‐labeled kraft lignin and in a deep‐tank fermentor using unlabeled kraft lignin. Among the fungi screened, A. fumigatus—isolated in our laboratories—was most potent in lignin biotransformation. Dialysis‐type fermentation, designed to study possible accumulation of low MW lignin‐derived products, showed no such accumulation. Recalcitrant carbohydrates like mi‐crocrystalline cellulose supported higher lignolytic activity than easily metabolized carbohydrates like cellobiose. An assay developed to distinguish between CO2 evolved from lignin and carbohydrate substrates demonstrated no stoichiometric correlation between the metabolism of the two cosubstrates. The submerged fermentations with unlabeled lignin are difficult to monitor since chemical assays do not give accurate and true results. Lignolytic efficiencies that allowed monitoring of such fermentations were defined. Degraded lignins were analyzed for structural modifications. A. fumigatus was clearly superior to C. versicolor in all aspects of lignin degradation; A. fumigatus brought about substantial demethoxylation and dehydroxylation, whereas C. versicolor degraded lignins closely resembled undegraded kraft lignin. There was a good agreement among the different indices of lignin degradation, namely, 14CO evolution, OCH3 loss, OH loss, and monomer and dimer yield after permanganate oxidation.
Protein separation by potential barrier chromatography
Authors: Ruckenstein E. , Lesins V.
Published: May 2005

Potential barrier chromatography (PBC) is a liquid chromatographic method in which the adsorption and desorption of proteins are controlled by modifications of repulsive double‐layer and attractive van der Waals interactions between the proteins and the adsorbent through changes in mobile phase composition. In this review PBC is compared and contrasted to the more traditional chromatographic methods, namely, ion exchange, gel permeation, hydrophobic interaction, and affinity chromatography. The physical forces that underlie PBC (as well as the other methods) are discussed in terms of their effects on chromatographic behavior. Experimental results are presented to illustrate the use and simplicity of the method.
The adsorption of Thiobacillus ferrooxidans on coal surfaces
Authors: Bagdigian Robert M. , Myerson Allan S.
Published: May 2005

The adsorption of Thiobacillus ferrooxidans to coal surfaces has been studied. Adsorption experiments were conducted on coal samples from eight different Eastern coal fields. In all cases the adsorption process was at least 90% complete within the first two minutes following inoculation. The results of these experiments were used to test the validity of two proposed adsorption models. The first model assumes that bacterial adsorption follows second‐order irreversible kinetics of the second kind with respect to the concentration of bacteria and substratum surface area in the system. The second model allows for the contribution of reversible adsorption detected in desorption experiments. It was found that the combined reversible–irreversible model more accurately describes the initial stages of adsorption. Rate constants in both models were calculated for each coal sample. The relation of each of these constants to the pyrite concentration in coal is presented and the significance of these relations is discussed.

Scanning electron micrographs of inoculated coal samples sho that Thiobacillus ferrooxidans selectively adsorb to exposed pyrite phases dispersed throughout the organic coal matrix. Preferential attachment was also observed along topographical faults in the caol surface. Mercury contact angle measurements on coal indicate that the selective adsorption of Thiobacillus ferrooxidans may be attributable to the lower surface free energy of pyrite relative to the organic coal matrix.
Alkali‐explosion pretreatment of straw and bagasse for enzymic hydrolysis
Authors: Puri V. P. , Pearce G. R.
Published: May 2005

Sugarcane bagasse and wheat straw were subjected to alkali treatment at 200°C for 5 min and at 3.45 MPa gas pressure (steam and nitrogen), followed by an explosive discharge through a defibrating nozzle, in an attempt to improve the rate and extent of digestibility. The treatment resulted in the solubilization of 40–45% of the components and in the production of a pulp that gave saccharification yields of 80 and 65% in 8 h for bagasse and wheat straw, respectively. By comparison, alkali steaming at 200°C (1.72 MPa) for 5 min gave saccharification yields of only 58 and 52% in 48 h. The increase in temperature from 140 to 200°C resulted in a gradual increase in in vitro organic matter digestibility (IVOMD) for both the substrates. Also, the extent of alkalinity during pretreatment appears to effect the reactivity of the final product towards enzymes. Pretreatment times ranging from 5 to 60 caused a progressive decline in the IVOMD of bagasse and wheat straw by the alkali explosion method and this was accompanied by a progressive decrease in pH values after explosion. In the alkali‐steaming method, pretreatment time had no apparent effect with either substrate. An analysis of the alkali‐exploded products showed that substantial amounts of hemicellulose and a small proportion of the lignin were solubilized. The percentage crystallinity of the cellulose did not alter in either substrate but there was a substantial reduction in the degree of polymerization. The superiority of the alkali‐explosion pretreatment is attributed to the efficacy of fiber separation and disintegration; this increases the surface area and reduces the degree of polymerization.
Direct evidence for a xylose metabolic pathway in Saccharomyces cerevisiae
Authors: Batt C. A. , Caryallo S. , Easson D. D. , Akedo M. , Sinskey A. J.
Published: May 2005

Xylose transport, xylose reductase, and xylitol dehydrogenase activities are demonstrated in Saccharomyces cerevisiae. The enzymes in the xylose catabolic pathway necessary for the conversion of xylose to xylulose are present, although S. cerevisiae cannot grow on xylose as a sole carbon source. Xylose transport is less efficient than glucose transport, and its rate is dependent upon aeration. Xylose reductase appears to be a xylose inducible enzyme and xylitol dehydrogenase activity is constitutive, although both are repressed by glucose. Both xylose reductase and xylitol dehydrogenase activities are five– to tenfold lower in S. cerevisiae as compared to Candida utilis. In vivo conversion of 14C‐xylose in S. cerevisiae is demonstrated and xylitol is detected, although no significant levels of any other 14C‐labeled metabolites (e. g., ethanol) are observed.
A mathematical model for cell separation technique of centrifugal elutriation
Authors: Barford J. P.
Published: May 2005

A mathematical model for the cell separation technique of centrifugal elutriation is developed. The model simulates both steady and non‐steady‐state operation of the elutriator. The model can be used to predict the required set of flow rates of elutriating liquid necessary to fractionate a cell culture, the required time of sampling before steady state is achieved, and the range of cell size/cell density combinations contained in any fraction. The model predictions were verified experimentally. Variations in cell density and cell size due to the suspending environment have a significant effect on the accuracy (although not the trends) of the model predictions. Quantification of these variations will lead to significantly more accurate model predictions. An enhanced separation method was developed using the model, to yield finer separation of a cell culture than previously possible. The use of the centrifugal elutriator may now be given a firm theoretical basis, with the quality of separation understood in terms of the basic theory of operation.
Immobilization of trypsin on alginic acid–poly (glycidyl methacrylate) graft copolymer
Authors: Reddy C. Raghuram , Reddy C. Rami , Raghunath K. , Joseph K. Thomas
Published: May 2005

Trypsin was immobilized onto alginic acid–poly(glycidyl methacrylate) graft copolymer (AAGMA). The resulting immobilized enzyme showed 65% of the soluble enzymatic activity. The temperature optimum was shifted by 5°C to a higher value. The pH optimum of immobilized enzyme has also been shifted by 0.5 units toward the alkaline side when compared to that of soluble enzyme. The pH stability and thermal stability are better than that of soluble enzyme.
Hexokinase activity as marker to assess time of harvest of foot‐and‐mouth disease virus in BHK21 Cl13 cell cultures
Authors: Suryanarayana V. V. S. , Banumathi N. , Rao B. U.
Published: May 2005

Hexokinase (B.C. 2.7.1.1) activity as a marker enzyme during FMD viral infection has been observed spectrophotometrically in a system coupled with glucose‐6‐phosphate dehydrogenase, in supernatants of BHK21Cl13 suspension as well as anchored cell culture at a minimum of 104 infective virus particles/ml. Specific activity increased with virus concentration in culture supernatants and abruptly decreased with a fall in virus titer, as has been noted by TCID/50,146 S concentration, and enzyme‐linked immunosorbent assay (ELISA) readings.
Immobilized phenylalanine hydroxylase through the SH groups
Authors: Koizumi Shinich , Takeuchi Tomio , Umezawa Hamao , Nagatsu Toshiharu
Published: May 2005

Purified rat liver phenylalanine hydroxylase [L‐phenylalanine:tetrahydropteridine:oxygen oxidoreductase (4‐hydroxylating), EC 1.14.16.1] was immobilized with activated thiol‐Sepharose 4B via disulfide bond formation, which is expected to immobilize the enzyme in its activated form through the SH modification. This immobilized enzyme was more stable against thermal denaturation than the free enzyme. When tetrahydrobiopterin was used as the natural cofactor, the Km value for phenylalanine was decreased and that for the cofactor was increased. Constant conversion from phenylalanine to tyrosine was demonstrated continuously for over 8 h at 25°C.
Sugar cane bagasse as a possible source of fermentable carbohydrates. II. Optimization of the xylose isomerase reaction for isomerization of xylose as well as sugar cane bagasse hydrolyzate to xylulose in laboratory‐scale units
Authors: Olivier S. P. , du Toit P. J.
Published: May 2005

Both the forward and backward reactions of xylose isomerase (Sweetzyme Q) with xylose and glucose as substrates have been studied in terms of kinetics and thermodynamics. The relationship between the two reactions can thus be determined. Much attention has been given to the reaction with xylose as substrate. The optimal conditions of the xylose reaction in terms of pH, buffer, metal ions, substrate concentration, temperature, and ionic strength have been determined. These findings did not differ much from those reported for the glucose reaction. Equilibrium constants for the aldose to ketose conversion were more favorable in the case of glucose. The results obtained with continuous isomerization of xylose in columns packed with either Sweetzyme Q or Taka‐Sweet were very similar to those obtained from batch isomerization processes. Particle size had a definite effect on reaction rate, which indicates that diffusion limitations do occur with the immobilized enzyme particles. Heat stability of Sweetzyme Q was good with t1/2 of 118, 248, and 1200 h at 70, 55, and 40°C, respectively. A novel method for the separation of xylose–xylulose mixtures with water as eluant on a specially prepared Dowex 1 × 8 column was developed. This technique has the capability of producing pure xylulose for industrial or research applications. A writ for a patent regarding this technique is at present prepared.
Granulation of biomass in thermophilic upflow anaerobic sludge blanket reactors treating acidified wastewaters
Authors: Wiegant W. M. , de Man A. W. A.
Published: May 2005

The development of granular sludge in thermophilic (55°C) upflow anaerobic sludge blanket reactors was investigated. Acetate and a mixture of acetate and butyrate were used as substrates, serving as models for acidified waste‐waters. Granular sludge with either Methanothrix or Methanosarcina as the predominant acetate utilizing methanogen was cultivated by allowing the loading rate to increase whenever the acetate concentration in the effluent dropped below 200 and 700 mg COD/L, respectively. The highest methane generation rates, up to 162 kg CH4‐COD/m3 day, or 2.53 mole CH4/L day, were achieved at hydraulic retention times down to 21 min, with granules consisting of Methanothrix. The formation of Methanothrix granules did not depend on the type of seed material, nor on the addition of inert support particles. The growth of granules proceeded rapidly with adapted seed material, even when the reactors were inoculated with low concentrations. With mesophilic seed materials growth of granules took much longer. Thermophilic Methanothrix granules strongly resemble mesophilic granules of the “filamentous” type. Some factors governing the thermophilic granulation process are discussed.
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

Material 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

The 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

A 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

Substrate‐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

Widely 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

The 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

Biomass 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

Five 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

The 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

The 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

In 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

This 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

Two 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

Thermostable 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

The 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

The 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.