bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of biodegradation of 2,4‐dichlorophenoxyacetate in the presence of glucose
Authors: Papanastasiou A. C. , Maier W. J.
Published: December 2004

Biodegradation of 2,4‐dichlorophenoxyacetate (2,4‐D) and glucose were studied using a 2,4‐D acclimated culture. Biodegradation of glucose by the 2,4‐D preacclimated culture follows the typical Monod kinetics after a 20‐h lag period in the presence or absence of 2,4‐D. Biodegradation of 2,4‐D by the same culture follows Andrew's “substrate inhibition” model. When both glucose and 2,4‐D are available, mutual inhibition is observed. However, the effect on 2,4‐D is masked by the fact that larger concentrations of active biomass are produced when glucose is available. This kind of concurrent utilization and interaction results in a substantial reduction of the mean cell residence time in a continuous flow system. It also extends the area of stability of the process into higher dilution rates as well as into higher influent concentrations.
Stability of glucose oxidase and catalase adsorbed on variously activated 13X zeolite
Authors: Pifferi P. G. , Vaccari A. , Ricci G. , Poli G. , Ruggeri O.
Published: December 2004

The use of 13X zeolite (0.1‐0.4‐mm granules), treated with 2N and 0.01N HCI, 0.01M citric acid, 0.1M citric‐phosphate buffer (pH 3.6), and in untreated form to adsorb glucose oxidase of fungal origin and microbial catalase was examined. Physicochemical analysis of the support demonstrated that its crystalline structure, greatly altered by the HCl and buffer, could be partially maintained with citric acid. The specific adsorption of the enzymes increased with decreasing pH and proved to be considerable for all the supports. The stability with storage at 25°C is strictly correlated with the titrable acidity of the activated zeolite expressed as meq NaOH/g and with pH value of the activation solution. It proved to be lower than 55 h for both enzymes if adsorbed on zeolite treated with 2N HCl, and 15‐fold and 30‐fold higher for glucose oxidase and catalase adsorbed, respectively, on zeolite treated with the 0.1M citric‐phosphate buffer and 0.01M citric acid. The specific adsorption of glucose oxidase and catalase was, respectively, 1840 U/g at pH 3.0 and 6910 U/g at pH 5.0. Their half‐life at 25°C with storage at pH 3.5 for the former and at pH 5.0 for the latter was 800 and 1560 h vs. 40 and 110 h for the corresponding free enzymes.
Continuous glutamate production using an immobilized whole‐cell system
Authors: Kim H. S. , Ryu Dewey D. Y.
Published: December 2004

For the purpose of saving the energy and raw materials required in glutamate fermentation, an immobilized whole‐cell system was prepared and its performance in a continuous reactor system was evaluated. Corynebacterium glutamicum (a mutant strain of ATCC 13058) whole cell was immobilized in K‐carrageenan matrix and the gel structure was strengthened by treatment with a hardening agent. The effective diffusivities of carrageenan gel for glucose and oxygen were found to decrease significantly with an increase in carrageenan concentration, while the gel strength showed an increasing trend. Based on the physical and chemical properties of carrageenan gel, the immobilization method was improved and the operation of the continuous reactor system was partially optimized. In an air‐stirred fermentor, the continuous production of glutamate was carried out. The effect of the dilution rate on glutamate production and operational stability were investigated. The performance of the continuous whole‐cell reactor system was evaluated by measuring glutamate productivity for a period of 30 days; it was found to be far superior to the performance of conventional batch reactor systems using free cells.
Continuous conversion of D‐xylose to ethanol by immobilized pachysolen tannophilus
Authors: Slininger P. J. , Bothast R. J. , Black L. T. , McGhee J. E.
Published: December 2004

The yeast Pachysolen tannophilus was entrapped in calcium alginate beads to ferment D‐xylose on a continous basis in the presence of high cell densities. Experimental operating variables included the feed D‐xylose concentration, the dilution rate, and the fermentor biomass concentration. Under favorable operating conditions, cultures retained at least 50% of their initial productivity after 26 days of operation. The specific ehanol production rate was dependent on the substrate level in the fermentor, passing through an optimum when the D‐xylose concentration was between 28 and 35 g/L. Consequently, reactor productivity increased with dilution rate and feed D‐xylose concentration until a maximum was reached. The ethanol content of the effluent always decreased with increasing dilution rate, but excessive dilution rates diminished the ethanol content without increasing productivity. Unlike production rate, ethanol yield declined monotonically from 0.35 g/g as the fermentor substrate concentration increased. The yield was 69% of that theoretically possible when the D‐xylose concentration was near zero, as opposed to 42% when it was in the range supporting the optimum specific rate of ethanol production. As long as D‐xylose was supplied to cells faster than they could consume it, productivity increased with the mass of cells immobilized. The effectiveness factor associated with the calcium alginte beads used in this system was 0.4, indicating that only 40% of the entrapped biomass was effective in converting D‐xylose to ethanol because of diffusion limitations.
Modeling of percolation process in hemicellulose hydrolysis
Authors: Cahela D. R. , Lee Y. Y. , Chambers R. P.
Published: December 2004

A mathematical model was developed for a percolation reactor in connection with consecutive first‐order reactions. The model was designed to simulated acid‐catalyzed cellulose or hemicellulose hydrolysis. The modeling process resulted in an analytically derived reactor equation, including mass‐transfer effects, which was found to be useful in process desing and reactor optimization. The modedl was verified by experimental data obtained from hemicellulose hydrolysis.
Conversion of pentoses by yeasts
Authors: Gong Cheng‐Shung , Claypool Tanya A. , McCracken Linda D. , Maun Christine M. , Ueng Pear P. , Tsao George T.
Published: December 2004

The utilization and conversion of D‐xylose, D‐xylulose, L‐arabinose, and xylitol by yeast strains have been investigated with the following results: (1) The majority of yeasts tested utilize D‐xylose and produce polyols, ethanol, and organic acids. The type and amount of products formed varies with the yeast strains used. The most commonly detected product is xylitol. (2)The majority of yeasts tested utilize D‐xylulose aerobically and fermentatively to produce ethanol, xylitol, D‐arabitol, and organic acids. The type and amount of products varies depending upon the yeast strains used. (3) Xylitol is a poor carbon and energy source for most yeasts tested. Some yeast strains produce small amounts of ethanol from xylitol. (4) Most yeast strains utilize L‐arabinose, and L‐arabitol is the common product. Small amounts of ethanol are also produced by some yeast strains. (5) Of the four substrates examined, D‐xylulose was the perferred substrate, followed by D‐xylose, L‐arabinose, and xylitol. (6) Mutant yeast strains that exhibit different metabolic product patterns can be induced and isolated from Candida sp. Saccharomyces cerevisiae, and other yeasts. These mutant strains can be used for ethanol production from D‐xylose as well as for the study of metabolic regulation of pentose utilization in yeasts.
Effects of mass‐transfer resistance on apparent stability and performance of fixed‐bed immobilized enzyme reactors: Theory and experiments with immobilized invertase
Authors: Ooshima Hiroshi , Harano Yoshio
Published: December 2004

Taking the hydrolysis of sucrose by invertase immobilized on anion‐exchange resin as an example, the effects of mass‐transfer resistance on the apparent stability of immobilized enzyme (IME) and the optimal policy for an IME reaction in a fixed‐bed reactor have been studied theoretically and experimentally. The following results were obtained: (1) The effect of mass‐transfer resistance on the effective deactivation rate of IME is summarized in two parameters concerning the intraparticle diffusion αp and the interparticle αf. (2) At a constant processed amount of raw materials, there exists an optimal flow rate of reaction fluid to enhance the reactor performance while the mass‐transfer resistance shifts the optimal point. (3) The intrinsic deactivation rate of IME has been estimated from the relationship between the fractional conversion at the reactor outlet and the operation time.
Characterization of the two‐phase systems in airlift tower–loop bioreactors during the cultivation of E. coli
Authors: Lippert J. , Adler I. , Meyer H. D. , Lübbert A. , Schügerl K.
Published: December 2004

During the cultivation of E. coli in an airlift tower–loop bioreactor, the following properties were measured: transverse profiles of Sauter bubble diameter, dS; local relative gas holdup, EG; bubble rise velocity, uBS; local mean velocity, ū turbulence intensity, u′; macrotime scale, TEL; dissipation time scale, τE; power spectrum, E(n); and energy dissipation spectrum D(n) at different distances from the aerator. The influence, distance from the aerator, absence and/or presnece of cells, and batch and/or continuous‐culture operation on the behavior of the two‐phase system are discussed on the basis of these properties.
Factors affecting cell attachment, spreading, and growth on derivatized microcarriers. I. Establishment of working system and effect of the type of the amino‐charged groups
Authors: Reuveny Shaul , Mizrahi Avshalom , Kotler Moshe , Freeman Amihay
Published: December 2004

A working system for studying the effects of factors involved in the chemical nature of microcarriers on cell attachment, spreading, and growth was established. The system is based on polyacrylamide beads, prepared by the emulsion polymerization technique. Sieved beads of desirable mean diameter were derivatized to generate controlled amounts of primary and tertiary amino groups. These microcarriers were used for the propagation of four different cell strains: BHK, MDCK, CEF, and MRC‐5. It was found that BHK cells attach and spread significantly faster on primary amino‐derivatized beads than those with tertiary amino groups, and at a lower degree of charging. Cell yields of MDCK cells (with pronounced epithelial morphology) propagated on primary amino‐derivatized beads were higher than that obtained for the tertiary amino‐derivatized microcarriers. On the other hand, CEF and MRC‐5 cells (with pronounced fibroblast morphology) achieved higher cell yields on the tertiary amino‐derivatized microcarriers.
Ethanol fermentation with cell recycling: Computer simulation
Authors: Lee J. M. , Pollard J. F. , Coulman G. A.
Published: December 2004

A mathematical model for glucose‐to‐ethanol fermentation at high yeast cell concentrations was developed. The feasibility of improving fermenter productivity over that of a conventional continuous‐stirred‐tank fermenter by using multiple stage reactors and yeast cell recycling was predicted by computer simulation. The optimum size distribution for multistage fermentors was obtained for different glucose feedstream concentrations and different glucose conversion levels. Productivity increases over a single‐stage reactor ranged from 1.2–2.0 times. The use of yeast cell recycling to increase cell concentration and productivity increases of over 4.0 times that of a system without recycling.
Anodic reactions in microbial fuel cells
Authors: Bennetto H. Peter , Stirling John L. , Tanaka Kazuko , Vega Carmen A.
Published: December 2004

Potentiometric and amperometric measurements were made with microbial fuel cells containing E. coli or yeast as the anodic reducing agent and glucose as the oxidizable substrate. The catalytic effects of thionine and resorufin on the anode reaction were investigated. Results on the potentiometry, polarization, and coulombic output of the cells support a mediator‐coupled mechanism for the transfer of electrons from the organism to the electrode in preference to a mechanism of “direct” electrochemical oxidation of glucose or its degradation products. Experiments with 14C‐labeled glucose show that when a microbial fuel cell produces a current under load, exogenous glucose is metabolized to produce 14CO2. The Coulombic yields of the cells indicate a high degree of energy conversion in these systems.
Growth and anthocyanin accumulation rates of carrot suspension cultures grown with excess nutrients after semicontinuous culture with different limiting nutrients at several dilution rates, pHs, and temperatures
Authors: Dougall D. K. , LaBrake S. , Whitten G. H.
Published: December 2004

When carrot cell cultures, after growth in semicontinuous culture, were transferred to media containing excess nutrients, they grew at different rates. The growth rates were generally higher after semicontinuous culture at higher dilution rates. There appears to be a limit on dilution rate above which growth rate does not increase. These changes were also displayed by clones from the parental culture. The possibility that these changes in growth rate reflect a need for the cultures to adapt to their new conditions is discussed. The growth rates of the cultures is markedly increased at 25°C compared with 22°C with little further increase at 28°C. Growth rate is altered by less than 20% when pH is changed from 4.5 to either 5.5 or 4.2. The rates of anthocyanin accumulation by the cultures were similar under all conditions tested except at 22°C. They were larger than the rates of dry weight accumulation. In contrast, the amounts of anthocyanin accumulated in the clones and in the parental cultures grown at pH 5.5 instead of pH 4.5 were very different. The observations were interpreted as showing that the clones differ in the rate of metabolism but not in the rate of synthesis of anthocyanins and that at pH 5.5 the rate of metabolism of anthocyanins but not the rate of synthesis is higher than it is at pH 4.5. The use of semicontinuous cultures as a source of inoculum for batch cultures rather than as a source of biomass for extraction of chemicals is discussed.
Kinetic and thermal characteristics of enzyme–graft copolymers
Authors: Cremonesi P. , D'Angiuro L.
Published: December 2004

The characteristics of horseradish peroxidase (HRP) immobilized onto Sepharose by a photochemical‐initiated graft copolymerization are presented. Active copolymers were synthesized using different amounts of glycidylmethacrylate (GMA), bisacryloylpiperazine (BAP), or 1,3,5‐hexhydrotriacryloyl‐s‐triazine (HTsT) as functional monomer. The activities, the K′m values (pGMA) copolymers: 0.53–0.76 × 10−4M; pBAP copolymers: 0.90–1.4 × 10−4; pHTsT copolymers: 1.8–2.6 × 10−4M and the thermal stabilities of the enzyme copolymers were strictly connected to the type of polymer. By varying the polymer amount present in a given copolymer, significant differences were found in the thermostability properties of pBAP and pHTsT copolymers both when checked in water or in phosphate buffer. No differences were found for pGMA copolymers. The samples in which there are the lowest pBAP or pHTsT content resulted the most stable. The activity retained after 240 min at 60°C by free HRP and pGMA–HRP was 30% whereas by pBAP–HRP and pHTsT‐HRP it was 50 and 75% of the original. Operational stability of the materials was in agreement with thermostability data. These results are discussed in terms of enzyme microenvironment which is strongly affected by the different network of the three polymers.
The use of the inverted linear model of enzyme decay to plan a strategy for enzymatic batch reactions and to assess the industrial applicability of immobilized enzyme preparations
Authors: Cardoso J. P. , Costa M. C.
Published: December 2004

This article is concerned with the development of a model to plan a strategy for an enzymatic batch process where enzyme is subjected to deactivation described by the inverted linear decay model. The particular system studied is the enzymatic hydrolysis of penicillin to 6‐amino penicillanic acid (6 APA), but the model can be utilized with other batch systems as long as the decay of the immobilized enzyme (IME) preparation is described by the inverted linear decay model. The model developed is eminently practical and simple and several example of its application are shown. Experimental data obtained in a small pilot plant batch recirculated reactor on the average are well fitted by this model. For IME systems whose decay is best described by the first‐order decay model, it is not possible to use the same approach.
Methanol bioconversion by Butyribacterium methylotrophicum—batch fermentation yield and kinetics
Authors: Datta Rathin , Ogeltree Jacqueline
Published: December 2004

Butyribacterium methylotrophicum is an anaerobic bacterium that can convert methanol to butyrate. This ability to produce longer‐chain carbon compounds from C1 substrates could be of commercial significance. The fermentation rates and product formation depend on the methanol/bicarbonate ratios during fermentation. The kinetics of batch fermentation fit the Luedeking‐Piret model with growth and maintenance associated product formation. Butyrate yield of 0.256 mol/mol methanol (ca. 85% of theoretical yield) has been obtained in batch fermentation.
Bioconversion of cellulose into ethanol by Clostridium thermocellum—product inhibition
Authors: Kundu S. , Ghose T. K. , Mukhopadhyay S. N.
Published: December 2004

Direct anaerobic bioconversion of cellulosic substances into ethanol by Clostridium thermocellum ATCC 27405 has been carried out at 60°C and pH 7.0 (initial for 100 L) under continuous sparging of oxygen free nitrogen in a culture vessel. Raw bagasse, mild alkali‐treated bagasse, and solka floc were used as substrates. The extent of conversion of raw bagasse (cellulose, 50%; hemicellulose, 25%; lignin, 19%) was observed as 52% (w/w) and 79% (w/w) in the case of mild alkali and steam‐treated bagasse (cellulose, 72%; hemicellulose, 11%; lignin, 12%), respectively. Use of bagasse concentration above 10 g/L showed a decreased rate in ethanol production. An inoculum age between 28–30 h and cell mass content of 0.027–0.036 g/L (dry basis) were used. The results obtained with raw and pretreated bagasse have been compared with those of highly pure Solka Floc (hemicellulose, 10%). Studies on the product inhibition indicated a linear fall of the percent of survivors with time. An Arrhenius type correlation between the cell decay rate constant and the product concentration was predicted. Even at low levels, the inhibitory effects of products on cell viability, the specific growth rate, and extracellular cellulase enzyme were observed.
Current practice in designing bottom‐entering fermentor drives
Authors: Wilson J. D. , Andrews T. E.
Published: December 2004

Top entering drives have become almost traditional for fermentor applications, however bottom entering drives have distinct features that merit consideration. The prinicipal advantages of bottom drives are delineated and design criteria discussed. Illustrations based on experience with several hundred fermentors ranging in power from fractional to 100 HP and in scale from 10 to 30,000 gallons are presented. Specific areas dealt with include configuration, alignment, seals, and shaft design.
Fermentation process air filtration via cartridge filters
Authors: Perkowski C. A.
Published: December 2004

The use of cartridge air filters for process air sterilization in commercial fermentation has proliferated in recent years. Sterile air cartridge filter performance is discussed. The use of dispersed oil particle (DOP) tests for in situ integrity testing is described and discussed.
Mass‐energy balance for microbial product synthesis—biochemical and cultural aspects
Authors: Minkevich I. G.
Published: December 2004

Interrelations between the rates of the product synthesis, cell biomass growth, respiration, and organic substrate consumption have been studied by the mass‐energy balance method. This method is based on the utilization of a special unit of substance reducity, namely redoxon. Biochemical parameters have been found which are involved in these interrelations and which describe the processes of high‐energy bond gain and energy expenditure during metabolism. In order to find these, the separation of the whole metabolism into several partial metabolisms has been applied. Equations have been obtained describing the dependences of the product yield and process specific productivity on the biochemical parameters and two macroscopic rates (e.g., rates of dilution and substrate consumption). Both aerobic and anaerobic product syntheses have been considered. The estimate of the upper limit of process productivity has been obtained. Mechanisms of the influence of the producer's intracellular characteristics on the rates of physiological processes and the culture productivity are discussed.
Analysis of protein distribution in budding yeast
Authors: Alberghina Lilia , Mariani Luigi , Martegani Enzo , Vanoni Marco
Published: December 2004

Flow cytometry is a fast and sensitive method that allows monitoring of different cellular parameters on large samples of a population. Protein distributons give relevant information on growth dynamics, since they are related to the age distribution and depend on the law of growth of the population and the law of protein accumulation during the cell cycle. We analyzed protein distributions to evaluate alternative growth models for the budding yeast Saccharomyces cerevisiae and to monitor the changes in population dynamics that result from environmental modifications; such an analysis could potentially give parameters useful in the control of biotechnological processes. Theoretical protein distributions (taking into account the unequal division of yeast cells and the exponential law of protein accumulation during a cell cycle) quantitatively fit experimental distributions, once appropriate variability sources are introduced. Best fits are obtained when the protein threshold required for bud emergence increases at each new generation of parent cells.
Effect of immobilization on stability and kinetic properties of α‐L‐fucosidase from Turbo cornutus
Authors: Cohenford Menashi A. , Urbanowski Joseph C. , Dain Joel A.
Published: December 2004

An amount of α‐L‐fucosidase from T. cornutus liver was copolymerized with glutaraldehyde using bovine serum albumin as the carrier protein. The properties of the native, the soluble enzyme polymer complex, and the insoluble enzyme polymer complex were studied and compared under various conditions of pH, temperature, substrate, and inhibitor concentration. Native α‐L‐fucosidase was heat labile and lost more than 85% of its activity when incubated at 55°C for 5 min. In contrast, under equivalent incubation conditions, both the soluble and the insoluble enzyme polymer complexes exhibited enhanced resistance to thermal inactivation and after 5 min lost only 65 and 40% of their original activity, respectively. Polymerzation also resulted in the shift of pH optima towards the acidic range, a decrease in activation energy and a change in the apparent Km values towards the p‐nitrophenyl‐α‐L‐fucopyranoside substrate.
Dependence of biological treatment rate on species composition in activated sludge or biofilm. I: A biological treatment model with ecosystem adaptation
Authors: Vavilin V. A. , Vasiliev V. B.
Published: December 2004

A biological treatment model with ecosystem adaptation (ESA model) is proposed as a means of describing multicomponent sewage treatment. The distribution of microorganisms which oxidize different components of the pollutant is strongly dependent on organic loading. The model can be used to compute multistep treatment systems with specific microflora at each step.
Theory and modelling of ethanol evaporative losses during batch alcoholic fermentation
Authors: Williams Lynn A.
Published: December 2004

Evaporative loss of ethanol during batch alcoholic fermentation has been modelled, employing modern concepts of kinetics and stoichiometry and the best available phase equilibrium thermodynamic data. Theoretical results demonstrate that loss is proportional to the second power of the sugar concentration utilized and that the logarithm of loss is proportional to reciprocal absolute temperature. Good agreement is demonstrated among the theory, the numerical model, and the literature results. A master correlation for predicting ethanol loss is presented.
Application of a noninhibitory growth model to predict the transient response in a chemostat
Authors: Chiam H. F. , Harris I. J.
Published: December 2004

A method of adapting a kinetic model based on steady‐state chemostat data to predict the transient performance of a chemostat culture is presented. The proposal provides for a time delay which can be considered equivalent to a period of reduced activity of the organism subsequent to the introduction of a step change in operating conditions. The adapted kinetic model gives substantially better performance in predicting the transient response of an experimental system than the unmodified kinetic model.
Growth and phosphate uptake of a high phosphate accumulating bacterium, Arthrobacter globiformis PAB‐6 in continuous culture
Authors: Tamatani Hiroaki , Shoda Makoto , Udaka Shigezo
Published: December 2004

A high phosphate accumulating bacterium, Arthrobacter globiformis PAB‐6, was grown in a chemostat under glucose‐limitation. Two different growth patterns at steady state with various dilution rates were obtained. In one case, cells having a coccus shape tended to washout at a low dilution rate, 0.2 (h−1). In another, cells with a rod shape grew faster and gave a good steady‐state growth at a dilution rate of 0.4. Such a close relationship between growth rate and cell morphology was found both in continuous and batch cultures. The amount of phosphate uptake per cell mass was almost constant irrespective of the dilution rate, but the rate of the uptake was maximum at about the dilution rate of 0.4. A clone of PAB‐6 was isolated from the continuous culture with high dilution rate and had maximum specific growth rate of 0.7 in a simple glucosesalt medium.
The kinetics of penicillin‐V deacylation on an immobilized enzyme
Authors: Haagensen P. , Karlsen L. G. , Petersen J. , Villadsen J.
Published: December 2004

An immobilized Penicillin‐V‐acylase (commercial name, Novozym 217) with high specificity for the phenoxyacetyl‐(V)‐ side chain was investigated in a recycle reactor and in a batch reactor to find the enzymatic reaction rate as a function of conversion, x, substrate concentration, c and pH. The reaction rate depends strongly on pH, and both products, phenoxy‐acetic acid and 6‐APA, inhibit the reaction. Nonspecific side reactions amount to only a few per cent when c <150mM and pH& gt; 6.5. The effectiveness factor for commercial‐size particles is found to be about 0.65, and a value of 1.3mM is obtained for the equilibrium constant, Keq, of the deacylation reaction. A kinetic model for the deacylation process which includes the effect of pH and of the reverse (acylation) reaction is proposed. Rate data for particles of different size are fitted to the nonlinear model. Five kinetic parameters and an effective diffusivity for the immobilized enzyme particles are determined.
The fission yeast Schizosaccharomyces pombe in continuous culture
Authors: Vraná Dagmar
Published: December 2004

The fission yeast Schizosaccharomyces pombe was cultivated in a chemostat at dilution rates of D = 0.03, 0.05, 0.10, and 0.20 h−1. After steady state had been reached, the amount of dry matter, number of cells, concentration of residual sugar, yield coefficient (Y), and some morphological properties of the cells were estimated. Curves reflecting the dry mass, number of cells, and cell mean volume show a changing coordination between the growth rate and the rate of cell division, with respect to D. In addition, it could be concluded that in dividing cells the cell septum is localized asymmetrically; Two nonidentical cells differing both in length and volume result. The degree of asymmetry is a function of the dilution rate.
The role of chitin in uranium adsorption by R. arrhizus
Authors: Tsezos Marios
Published: December 2004

In order to further refine and support the uranium biosorption mechanism hypothesis proposed for Rhizopus arrhizus, uranium competitive equilibrium uptake isotherms by chitin were determined at two different solution pH levels and in the presence of different concentrations of competing ions, namely, Cu2+, Zn2+, and Fe2+. The co‐ion effect became more poronounced as the co‐ion concentration in solution and pH increased. Obtained equilibrium data are in agreement with uranium biosorption data reported earlier. Infrared, mass, and electron paramagnetic resonance (EPR) spectra of chitin before and after uranium uptake in the presence of the competing ions Cu2+, Zn2+, and Fe2+ were recorded. The combination of the spectral data and the information from equilibrium studies supported the hypothesis advanced earlier on the mechanism of uranium uptake by R.arrhizus. In addition, the data suggested the participation of a free radical in uranium coordination by the cell wall chitin. The mechanism of reduction of the uranium uptake capacity of the biomass in the presence of competing ions was also elucidated further.
Alkali treatment of corn stover to improve sugar production by enzymatic hydrolysis
Authors: MacDonald Douglas G. , Bakhshi Narendra N. , Mathews Joseph F. , Roychowdhury Anjali , Bajpai Pratima , Moo‐Young Murry
Published: December 2004

Alkali treatment of corn stover improves the avaliability of cellulose and hemicellulose for enzymatic attack. Treatments were carried out for 1 to 60 min at temperatures and NaOH concentrations ranging from 100 to 150°C and 0 to 2%, respectively. Solubilization of the stover and sugar production by enzymatic hydrolysis (Trichoderma viride cellulase) of the solid residue and the dissolved solids were used to measure the effect of caustic treatment. At 150°C and 2% NaOH concentration, 65% of the original stover was dissolved after 5 min and 52% saccharificatin (g sugar/g stover) of the residue and dissolved solids by enzymatic hydrolysis was achieved compared to 20% for untreated corn stover.
Stopped‐flow kinetic studies of the cellulase‐catalyzed conversion of cellulose to glucose
Authors: Banerjee D. K. , Laidler K. J.
Published: December 2004

The kinetics of the cellulase‐catalyzed conversion of soluble cellulose into glucose have been studied over a range of substrate concentrations and temperatures, and at pH values ranging from 4.75 to 7.0. Lineweaver‐Burk plots were linear and led to V = 6.2μM/s and Km = 13.1 mM at pH 5.8 and 25.0°C. The pK values corresponding to the free enzyme are 4.8 and 6.8 and are consistent with carboxyl and imidazole groups as the active ionizing species. These pK values were little changed in the enzyme‐substrate intermediate that reacts in the ratedetermining step, suggesting that the ionizing groups are still free in this intermediate. The activation energy corresponding to V/Km is 80.6 kJ/mol, and that corresponding to V is 38.7 kJ/mol. The corresponding entropies of activation are 21 J K−1 mol−1 and –157 J K−1 mol−1, respectively.
Properties and application of immobilized β‐D‐glucosidase coentrapped with Zymomonas mobilis in calcium alginate
Authors: Lee James M. , Woodward Jonathan
Published: December 2004

The enzyme β‐D‐glucosidase has been immobilized on concanavalin A‐Sepharose to give a maximum loading of 2050 units/g dry weight of support material. The immobilized β‐D‐glucosidase was also entrapped within calcium alginate gel spheres with apparently only 35% retention of activity when assayed with 10mM cellobiose. However, it was discovered that, unlike the immobilized enzyme, the entrapped immobilized enzyme was not subject to substrate inhibition up to 100mM cellobiose, suggesting that a concentration gradient of cellobiose existed between the bulk solution and the interior of the gel sphere. Thus, the activity of the entrapped immobilized enzyme was almost twice as high as that of the immobilized enzyme when assayed with 100mM cellobiose. Concanavalin A‐Sepharose‐immobilized β‐D‐glucosidase and the bacterium Zymomonas mobilis coimmobilized in calcium alginate gel spheres converted cellobiose to ethanol in both batch and continuous‐flow fermentation systems.
A new function for overall optimization of yeast production
Authors: Klibansky Miriam M. , Otero Miguel A. , González Leonel F.
Published: December 2004

The influence of several operating variables on the productivity and nutritional quality of Candida utilis under carbon‐limited growth conditions was studied. Four responses were analyzed: biomass yield (Y), in vitro dry matter digestibility (d), nucleic acid cotents, and protein content (P). Three operating variables were studied: dilution rate, temperature, and carbon‐nitrogen ratio in the growth medium. Correlation describing the influence of operating variables on the studied response parameters were developed. From these correlations response surfaces were drawn. A new function, α = PdY, is proposed as a more comprehensive criterion for selecting the optimal conditions under the constraint of satisfying multiple objectives. It is demonstrated to be superior to the yield coefficient alone in this respect, since it accounts for factors that are important to the nutritional aspects of the process.
The macrokinetics of an enzymatic system containing an enzyme that inactivates in the course of reaction
Authors: Sud'ina G. F. , Kobel'kov G. M. , Varfolomeev S. D.
Published: December 2004

The work describes the action of a heterogenous multisubstrate enzymatic system under conditions involving inactivation of the enzyme. A nonsteady‐state kinetic model has been suggested for description of the system. It has been found that the time dependence of the product flow from the membrane is a curve with a maximum which falls on a time equal to the reverse inactivation constant. It has been shown that the efficiency of such systems increases as does the time of the operation of the enzyme.
Utilization of statistics and experimental design in data collection and analysis
Authors: Solomon B. O. , Erickson L. E. , Yang S. S.
Published: December 2004

Application of experimental design techniques to Pirt's yield model shows that it is important to collect data at the lowest and highest specific growth rates. In the fed‐batch fermentation process, values of specific growth rate can be varied from the maximum value at the start of the process to very low values near the end of the experiment.Candida utiliswas cultivated using batch followed by fed‐batch culture with glucose as the main source of carbon and energy. Values of substrate concentration, oxygen consumption, carbon dioxide evolution, liquid volume, flow rate cell concentration, and nitrogen concentration, which was an indirect measure of biomass, were measured. Least‐squares estimates of the true biomass energetic yield and maintenance coefficient were obtained using a multivariate statistical analysis procedure referred to as the covariate adjustment procedure. Methods of selecting the best estimates using covariate adjustment are illustrated. The results show that useful parameter estimates with relatively short confidence intervals can be obtained using these statistical methods.
Kinetic studies of enzymatic hydrolysis of insoluble cellulose: Derivation of a mechanistic kinetic model
Authors: Fan L. T. , Lee Yong‐hyun
Published: December 2004

A comprehensive mechanistic kinetic model for enzymatic hydrolysis of insoluble cellulose has been synthesized by combining models for several key aspects which have been derived independent of each other. The model takes into account the major contributing factors: the nature of the enzyme system, the structure of cellulose, and the mode of interaction between the enzyme and cellulose molecules. It consists of a set of simultaneously occurring ordinary differential equations with ten kinetic constants. All of the kinetic constants have been determined independently by carrying out critically designed experiments, and they appear in the comprehensive model without any arbitrary manipulations. The governing equations of the model have been numerically simulated by means of the computer subroutine CSMP III. The model predicts the progress of hydrolysis of cellulose over a wide range of experimental conditions and hydrolysis times reasonably well. The model can even be applied to predict the progress of hydrolysis for intensively pretreated cellulose with a minor adjustment. The applicability of the model for the actual process development is also discussed.
Substrate‐to‐biomass ratio as a process control parameter in heterogeneous populations growing on complex substrates
Authors: McLoughlin Aiden J. , Crombie‐Quilty Mary B.
Published: December 2004

The removal of a complex substrate bovine serum albumin (BSA) by activated sludge was examined with respect to the initial level of substrate adsorbed, the rate of substrate removal, and the induction of exoprotease (located both on the sludge matrix and in the cell‐free supernatant). The relationship of these various processes, which together make up the overall removal process, was investigated with respect to the level of substrate present expressed both per unit volume and per unit biomass. A higher degree of correlation was observed when the substrate per unit biomass (S/B) ratio was used, thus providing some basis for empirical models of the activated sludge system based on the food‐to‐microorganisms (F/M) ratio. The interaction of sludge concentration and substrate concentration, plus the fact that there is not a clear distinction, as in pure culture, between substrate and microorganisms, makes the use of models devised for pure culture questionable.
Development of a culture medium for large‐scale production of cellulolytic enzymes by Trichoderma reesei
Authors: Warzywoda M. , Ferre V. , Pourquie J.
Published: December 2004

Culture filtrates of CL‐847 strain of Trichoderma reesei grown on different carbon sources have been compared. The highest enzyme production is obtained with Whatman C 41 cellulose: 17.9 mg/mL of soluble proteins and 13.7 units of filter paper (FP) activity. Wood pulps gave lower production values and more viscous culture media. About one‐third of maximal enzyme production is obtained on lactose as the sole carbon source. Addition of 0.5% cellulosic inducer to 6% lactose media enhances enzyme production up to the following levels: 14.1 mg/mL of soluble proteins and 8.4 units of FP activity.
A generalized kinetic model for the study of microbial growth
Authors: Hiss Haroldo , Borzani Walter
Published: December 2004

The following general equation is proposed to represent the kinetics of microbial growth

,
where ϕ and ψ depend on several parameters of the fermenting system. The values of ϕ and ψ were calculated based on results obtained in a batch lactic acid fermentation, a batch cultivation of yeast on diesel oil, and a continuous cultivation of yeast on sugarcane molasses.
Adsorption of cellulase from Trichoderma viride on cellulose
Authors: Ooshima Hiroshi , Sakata Masaru , Harano Yoshio
Published: December 2004

The adsorption of cellulase from Trichoderma viride (Meicelase CEP) on the surface of pure cellulose was studied. The adsorption was found to obey apparently the Langmuir isotherm. From the data concering the effects of temperature and the crystallinity of cellulose on the Langmuir adsorption parameters, the characteristics of the adsorption of the individual cellulase components, namely CMCase (endoglucanase) and Avicelase (exoglucanase), were discussed. While β‐glucosidase also adsorbed on the surface of cellulose at 5°C, it did not at 50°C.
Biological oxidation of organic constituents in tar–sand combustion‐process water
Authors: Torpy M. F. , Luthy R. G. , Raphaelian L. A.
Published: December 2004

A study was performed to characterize a sample of reverse‐forward, tar‐sand combustion process water, and to conduct an initial evaluation of activated sludge treatment of the process water. No pretreatment of the wastewater was considered necessary prior to biological oxidation other than addition of ca. 0.006M caustic/L influent to maintain reactor pH in the desired range of 7.0–7.5. The process water was treated successfully by biological oxidation, achieving an 88% reduction of both COD and soluble organic carbon and a 97% reduction of BOD. The disposition of about 150 organic compounds was evaluated and it was shown that a variety of carboxylic acids and aromatic compounds were removed by treatment. Quinolines and certain higher molecular weight carboxylic acids were not removed as effectively as other compounds. These preliminary results should assist in the design of future investigations with tar‐sand process water for purposes of optimizing process treatment and improving sample characterization.
Preparative resolution of D,L‐threonine catalyzed by immobilized phosphatase
Authors: Scollar Mark P. , Sigal George , Klibanov Alexander M.
Published: December 2004

Hydrolysis of L‐ and D‐O‐phosphothreonines catalyzed by four different phosphatases, alkaline phosphatases from calf intestine and E. coli and acid phosphatases from wheat germ and potato, has been kinetically studied. Alkaline phosphatases were found to have comparable reactivities towards the optical isomers. On the other hand, both acid phosphatases displayed a marked stereoselectivity, hydrolyzing the L‐ester much faster than its D counterpart. Wheat germ acid phosphatase was the most stereoselective enzyme: VL/VD = 24 and Km,L/Km,D = 0.17. This enzyme was immobilized (in k‐carrageenan gel, followed by crosslinking with glutaraldehyde) and used for the preparative resolution of D,L‐threonine: the latter was first chemically O‐phosphorylated and then asymmetrically hydrolyzed by the immobilized phosphatase. As a result, gram quantities of L‐threonine of high optical purity and O‐phospho‐D‐threonine were prepared. Immobilized wheat germ phosphatase has been tested for the resolution of other racemic alcohols: serine, 2‐amino‐1‐butanol, 1‐amino‐2‐propanol, 2‐octanol, and menthol. In all those cases, the enzyme was either not sufficiently stereoselective or too slow for preparative resolutions.
Mathematical simulation of pseudo‐crystallofermentation of hydrocortisone by Arthrobacter simplex
Authors: Chen Kuo‐Cheng , Chang Ching‐Chuan , Chiu Chuang‐Fan , Ling Alvin C.
Published: December 2004

A mathematical model has been developed to simulate the pseudo‐crystallofermentation process of hydrocortisone by Arthrobacter simplex. The model describing the process included considerations on the kinetics of microbial growth, the rate of enzyme formation, the rate of substrate dissolution, the rate of solute crystallization, and the kinetics of enzymatic reaction. The system of equations was solved numerically by the Runge‐Kutta‐Gill method. The good agreement between prediction and experiment indicated the reliability of the established model. The simulation was capable of predicting the time when the crystallization of product occurred, which could be further verified by microscopic observation on the culture medium, as well as cell growth, enzyme synthesis, product formation, and the composition of the final product crystals.
Enzymatic hydrolysis and fermentation of corn for fuel alcohol
Authors: Mullins J. Thomas
Published: December 2004

The integration of enzyme saccharification with fermentation reduces the total time required to produce acceptable levels of ethanol. The use of a more concentrated mash (84.8 L total mash/bu corn) results in a 26.6% increase in ethanol productivity and a 21.4% increase in beer ethanol concentration compared to standard corn mash (96.6 L total mash/bu corn). Thus, the energy requirement and cost of distillation can be reduced. The addition of waste cola syrup at 30 g invert sugar/L total mash gave a 19% increase in ethanol concentration in the final beer and required only a small increase in the period of fermentation. Surplus laundry starch can replace 30–50% of the weight of corn normally used in fermentation without influencing ethanol production or the time required for fermentation. Both of these waste materials reduce the unit cost of ethanol and demonstrate the value of such substances in ethanol systems.
Effect of different gas environments on bench‐scale solid state fermentation of oat straw by white‐rot fungi
Authors: Levonen‐Munoz Eeva , Bone Derek H.
Published: December 2004

Three white‐rot fungi, Phanerochaete chrysosporium, Polyporus tulipiferae, and Polyporus sp. A336 were grown on 100‐g amounts of chopped oat straw in gassed 4.5 L (diameter 16 cm, height 23 cm) solid‐state reactors for two weeks. The different gas atmospheres were regulated by (1) air diffusion through foam plugs, (2) intermittent or continuous air flow, (3) intermittent oxygen, 50 or 100% continuous oxygen flow, and (4) continuous 10% carbon dioxide in oxygen flow. The fermented straw was analyzed for total weight loss, Klason lignin loss, and enzymatic (cellulase) hydrolysis. P. chrysosporium grown on straw in continuous oxygen at 35°C caused a 41% weight loss and 33.5% hydrolysis was obtained when the pretreated straw was hydrolyzed with cellulase enzyme. P. tulipiferae caused a 27% weight loss and 34.3% cellulase hydrolysis in the straw at 30°C. Polyporus sp. A336 selectively degraded lignin of the straw and under intermittent oxygen resulted in an 18% weight loss and 33.6% cellulase hydrolysis at 35°C. When the straw was supplemented with 10% xylose (straw basis) and was continuously gassed with 50% oxygen, Polyporus sp. A336 produced a 14.5% weight loss and 38.7% cellulase hydrolysis. Oxygen and carbon dioxide exchange rates were measured for some of these bench‐scale fermentations.
Studies on chemically aggregated pepsin using glutaraldehyde
Authors: Khan Seemi S. , Siddiqi A. M.
Published: December 2004

Porcine pepsin was immobilized by chemical aggregation using glutaraldehyde as a bifunctional crosslinking agent. The immobilzed pepsin followed Michaelis–Menten kinetics (Km = 5.3 × 10−5 M) and the yield of immobilization was 91%. The activation energy of the immobilized preparation was 90,613 cal/mol as compared to 67,532 cal/mol for native pepsin. Using acid‐denatured hemoglobin and N‐acetyl phenyl‐alanyl‐3, 5‐diiodotyrosine (APDT) as substrates, the activities shown by the immobilized pepsin were, respectively, 67 and 79% that of the soluble pepsin. The immobiized pepsin showed marked stabilization against pH, temperature, urea, and guanidine hydrochloride. The activity of the immobilized preparation in the presence of urea was greater when hemoglobin was used as the substrate than when APDT was used as substrate. Storage of the preparation under refrigerated conditions for 160 days showed 58% retention in enzyme activity. The immobilized pepsin can be removed from the reaction mixture volume easily, retaining nearly 100% of its activity even after being used in seven consecutive assays.
Suggestions for the operation of radial flow cells in cell adhesion and biofouling studies
Authors: Fryer P. J. , Slater N. K. H. , Duddridge J. E.
Published: December 2004

An analysis of the radial flow cell is presented to show that the assumption of creeping laminar flow should be used cautiously. Simple models which account for the influence of fluid inertial forces over most of the width of the plate are reviewed. A modified Reynolds number is introduced which may be used to test the validity of the creeping flow solution.