bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between the fine structure of native cellulose and cellulose degradability by the cellulase complexes of Trichoderma reesei and Clostridium thermocellum
Authors: Weimer Paul J. , Weston Wayde M.
Published: December 2004

The initial rate of hydrolysis of six commercially available native (type l) celluloses was determined for the crude cellulase complexes of the thermophilic anaerobic bacterium C. thermocellum and the mesophilic fungus T. reesei. These rates were then compared with certain physical features of the substrates in an attempt to determine the role of cellulose structure in its degradability. Within the substrate series tested, the Clostridium system showed a greater relative range in rate of enzymatic hydrolysis than did the Trichoderma system. Average correlation coefficients for the kinetic rates from bacterial and fungal cellulases, respectively, and the following physical parameters were obtained: relative crystallinity index (RCl) from acid hydrolysis, −0.61 and −0.85; RCl from x‐ray diffraction, −0.75 and −0.89; accessibility to formylation at 4°C, + 0.49 and +0.60; nonaccessibility to formylation at 65°C, −0.40 and −0.73; fiber saturation point, + 0.83 and + 0.85. Kinetic and pore volume distribution data suggest that the rate‐limiting components of both the bacterial and fungal cellulase systems are of similar size, approximately 43 Å along one axis.
Utilization rates of trace halogenated organic compounds in acetate‐grown biofilms
Authors: Bouwer Edward J. , McCarty Perry L.
Published: December 2004

Trace concentrations of chlorinated benzenes and chlorinated aliphatics were biotransformed by acetate‐supported biofilms, the former under aerobic conditions and the latter under methanogenic conditions. The rates of transformation of the halogenated organic compounds (secondary substrates) differed from that of acetate, the primary substrate; some were higher, some were lower, and some were similar. Factors affecting the relative rates of utilization in multisubstrate systems are not known.
A kinetic model for product formation in unstable recombinant populations
Authors: Lee Sun Bok , Seressiotis Alex , Bailey James E.
Published: December 2004

A mathematical model has been formulated for product formation by unstable recombinant organisms in batch and in continuous flow reactors. The cell population is characterized by three different genotypes according to the absence or presence of plasmids (segregational instability) and of active cloned gene (structural instability). Empirical growth inhibition factors due to plasmids and to product protein are assigned to the corresponding strains. Product formation kinetics are based upon a quasi‐steady‐state transcription–translation expression model. An approximate form of these mechanism‐based product formation kinetics is identical to the traditional, empirically based Leudeking–Piret formula. Alternative models which consider inhibition based on overall product concentration and based on intracellular product concentration are posed, and their implications are compared. Simulation results based on these models indicate (1) overall plasmid stability depends on product expression and reactor operating conditions as well as on intrinsic segregation and mutation rate parameters; (2) there exists an optimum combination of plasmid copy number and cloned‐gene transcription and translation efficiencies to maximize reactor productivity; and (3) continuous reactor dilution rate influences the fraction of productive cells. General trends and substrate, product, and cell concentration time trajectories obtained from model simulation agree well qualitatively with currently available experimental information.
Effect of shear on membrane‐associated enzymes: Studies of the release of intracellular protein and of the progesterone 11α‐hydroxylase complex from rhizopus nigricans
Authors: Talboys B. L. , Dunnill P.
Published: December 2004

Rhizopus nigricans ATCC 6227b grown in either shake flasks or a fermentor was sheared in a concentric cylinder viscometer. The cells grown in shake flasks were found to be more susceptible to disruption by shear than those grown in the fermentor. Cells resuspended in a medium containing reduced glutathione and EDTA were found to be more easily disrupted than cells resuspended in 0.5% NaCl. The optimum condition for disruption of shake flask cells grown in the former medium with retention of progesterone 11α‐hydroxylase activity was a laminar shear rate of 4300 s−1, for a period of 3 min at 4°C. During the first 30 s the apparent viscosity was found to decrease significantly with applied shear.
Grain sorghum stillage recycling: Effect on ethanol yield and stillage quality
Authors: Egg Richard P. , Sweeten John M. , Coble Charlie G.
Published: December 2004

Stillage obtained from ethanol production of grain sorghum was separated into two fractions: thin stillage and wet solids. A portion of the thin stillage was recycled as cooking water in subsequent fermentation runs using both bench‐ and full‐scale ethanol production plants. When thin stillage replaced 50–75% of the cooking water, large increases occurred in solids content, COD, and EC of the resulting thin stillage. It was found that while the volume of thin stillage requiring treatment or disposal was reduced, there was little reduction in the total pollutant load. Stillage rcycling had little effect on the quality of the stillage wet solids fraction. At the high levels of stillage recycle used, ethanol yield was reduced after three to five runs of consecutive recycling.
Extraction chemistry of fermentation product carboxylic acids
Authors: Kertes A. S. , King C. J.
Published: December 2004

Within the framework of a program aiming to improve the existing extractive recovery technology of fermentation products, the state of the art is critically reviewed. The acids under consideration are propionic, lactic, pyruvic, succinic, fumaric, maleic, malic, itaconic, tartaric, citric, and isocitric, all obtained by the aerobic fermentation of glucose via the glycolytic pathway and glyoxylate bypass. With no exception, it is the undissociated monomeric acid that is extracted into carbon‐bonded and phosphorus‐bonded oxygen donor extractants. In the organic phase, the acids are usually dimerized. The extractive transfer process obeys the Nernst law, and the measured partition coefficients range from about 0.003 for aliphatic hydrocarbons to about 2 to 3 for aliphatic alcohols and ketones to about 10 or more for organophosphates. Equally high distribution ratios are measured when long‐chain tertiary amines are employed as extractants, forming bulky salts preferentially soluble in the organic phase.
A semicontinuous culture model that links cell growth to extracellular nutrient concentration
Authors: Quinlan Alician V.
Published: December 2004

During semicontinuous culture, a sample of fixed volume is removed at regular time intervals to make measurements and/or harvest culture components, and an equal volume of fresh medium is immediately added to the culture, thereby instantaneously enhancing nutrient concentrations and diluting cell concentration. The resulting cell concentration versus time curve (i.e., the actual cell growth curve) has a saw‐toothed appearance because of the periodic dilution of cell concentration. The observed cell concentrations correspond to the peaks of the saw‐toothed curve. Cell growth rates are estimated from the locus of observed cell concentrations (i.e., from the apparent growth curve obtained by connecting the peaks of the saw‐toothed curve). The sole preexisting model (Fencl's mode) for estimating cell growth rate is valid only when the cells are growing exponentially at a constant rate between samplings. This model has limited validity: despite the periodic enhancement of nutrient concentration, cell growth between samplings eventually causes nutrient depletion, and the cells cease to grow exponentially. Failure to recognize the limits of validity for Fencl' model has resulted in many erroneous applications of the model and, consequently, many incorrect estimates of cell growth rates. To provide a means for correctly estimating cell growth rates, Fencl's exponential model was extended, and a new model that describes the effects of nutrient depletion on cell growth in semi‐continuous culture was obtained. The new model shows that exhaustion of a single growth‐limiting nutrient in semicontinuous culture causes the locus of cell concentrations observed at time intervals of Δt to follow a logistic growth curve. The actual cell growth rate was shown to equal the apparent logistic growth rate plus the effective dilution rate −Δt−1 In (1 − f), where f is the ratio of sample volume to total culture volume. Moreover, the model predicts that both the apparent logistic growth rate and the apparent steady‐state cell concentration should rise linearly with the concentration of growth‐limiting nutrient in the input medium, but fall linearly with increases in the effective dilution rate. The new logistic model for nutrient‐limited cell growth in semicontinuous culture was successfully tested using published data for Asterionella formosa, Cyclotella meneghiniana, Daucus carota, and strain L mouse cells.
Enzymatic production of L‐serine with a feedback control system for formaldehyde addition
Authors: Hsiao Humg‐Yu , Wei Tena
Published: December 2004

Serine hydroxymethyltransferase (SHMT) in the form of crude extract from a recombinant strain of Klebsiella aerogenes was used for the production of L‐serine from glycine and formaldehyde (HCHO). A stirred tank bio‐reactor with a continuous feed of HCHO (37%) was employed. Since the performance of the serine bioreactor was heavily dependent on how HCHO was fed, an automatic feedback control system was developed for HCHO delivery utilizing the phenomenon of formol titration. This control procedure was based on the following circumstance: as a bioconversion proceeded, if the rate of HCHO feed was balanced by the rate of serine synthesis so that HCHO concentration was maintained near zero, then there was no pH change in the bioreactor. Once the rate of HCHO addition exceeded that of serine synthesis, the HCHO concentration built up and the excess HCHO reacted with the amino group of an amino acid (e.g. glycine or serine) to produce a Schiff base and a proton which lowered the pH. A pH controller detected and relayed this pH change to the on–off switch of the HCHO feed pump. Thus, HCHO infusion stopped when the pH was lower than the set point, which was the initial pH of the reaction. With this control system, the maximum concentration of HCHO that was reached in the bioreactor was only 1mM–3.3mM depending on the pH and amino acid composition in the bioreactor. Moreover, a decrease in pH also signaled the use of a slower feed rate at which HCHO was to be, delivered once the pH resumed its initial value after excess HCHO was consumed by the reaction. Employing this control system, we have optimized the performance of the serine bioreactor to give a serine titer of 450 g/L with an 88% molar conversion of glycine at a volumetric serine productivity of 8.9 g/L/h.
Saccharification of concentrated brewing bagasse slurries with dilute sulfuric acid for producing acetone–butanol by Clostridium acetobutylicum
Authors: Juanbaró Josep , Puigjaner Lluis
Published: December 2004

A comprehensive kinetic study of the acid hydrolysis of concentrated brewing bagasse slurries was performed. The use of the simple series reaction model was found to be suitable when a “heterogeneous correction” (pseudosubstrate‐inhibition) is taken into account in slurries with low liquid‐to‐biomass ratios. Rate constants are shown to be dependent not only on temperature and acid concentration but essentially also on the initial biomass concentration. Actual rate constants, activation energies, and acid and substrate reaction orders are reported for xylan, arabinan, and α‐glucan acid saccharification. There is a threshold acid loading necessary to overcome the 80% conversion, but no threshold has been found to overcome the “neutralizing” property of cellulosic materials. Reversible acid capture from brewing bagasse has been postulated. The highest monosccharide concentration into hydrolyzates has been found (65 g/L) after 10 h treatment, but economic considerations led us to treat a mean‐concentrated slurry (156 g/L) with 0.3M H2SO4 at 96°C, thus obtaining 45.5 g/L monosaccharides in 5 h with 50% less furfural content. After pH regulation only, growth of Clostridium acetobutylicum has been obtained, although complete sugar comsumption has not been achieved. Experiments are now underway to reach complete digestion and to investigate the increase of enzymic accessibility into residual substrate rich in cellulose.
Anaerobic digestion of high‐strength cheese whey utilizing semicontinuous digesters and chemical flocculant addition
Authors: Barford J. P. , Cail R. G. , Callander I. J. , Floyd E. J.
Published: December 2004

Semicontinuous digesters were used to anaerobically treat high‐strength whey (70 kg/m3·COD). A maximum loading of 16.1 kg COD/m3·day was obtained with soluble COD removal efficiencies greater than 99%. The use of a chemical flocculant resulted in an increased biomass concentration in the digester compared to a control, thus enabling correspondingly higher space loadings to be applied. With the onset of substantial levels of granulation of the biomass, flocculant dosage was able to be discontinued. This article discusses the performance of the digesters in detail and, briefly, the long‐term operational difficulties experienced and the control strategies employed on such systems.
Modeling the liquid flow in up‐flow anaerobic sludge blanket reactors
Authors: Bolle W. L , van Breugel J. , van Eybergen G. C. , Kossen N. W. F. , Zoetemeyer R. J.
Published: December 2004

By means of stimulus‐response experiments an Li+ tracer, models for the fluid flow in a 30‐m3 UASB reactor, used for the anaerobic treatment of wastewater, were tested. From the model with the best fit it could be derived that both the sludge bed and the sludge blanket can be described as perfectly mixed tank reactors with short‐circuiting flows; the settler volume acts like a plug‐flow region.

Apart from the volumes of the different flow regions, two parameters are necessary and sufficient to describe the fluid flow in a well functioning UASB reactor, i.e., the short‐circuiting flow over the sludge bed and the short‐circuiting flow over the sludge blanket. The volumes could be measured accurately.

The short‐circuiting flow over the sludge bed is a linear function of the sludge bed height. When the optimal height of the sludge bed is defined as the height for which the short‐circuiting flows are as small as possible, a bed‐height of 3.5–4 m is sufficient (for superficial gas velocities between 1 and 1.5 m/h). This is in contradiction to the results of other authors. The short‐circuiting flows over the sludge bed and the sludge blanket were also influenced by the superficial gas velocity.
Immobilization of Enzyme into Poly(vinyl alcohol) Membrane
Authors: Imai Kiyokazu , Shiomi Tomoo , Uchida Kozo , Miya Masamitsu
Published: December 2004

Glucoamylase, invertase, and cellulase were entrapped within poly(vinyl alcohol) (PVA) membrane cross‐linked by means of irradiation of ultraviolet light. The conditions for immobilization of glucoamylase were examined with respect to enzyme concentration in PVA, sensitizer (sodium benzoate) concentration in PVA, irradiation time, and membrane thickness. Various characteristics of immobilized glucoamylase were evaluated. Among them, the pH activity curve for the immobilized enzyme was superior to that for the native one, and thermal stability was improved by immobilization with bovine albumin. The apparent Km was larger for immobilized glucoamylase than for the native one, while Vmax was smaller for the immobilized enzyme. Also, the apparent Km appeared to be affected by the molecular size of the substrate. Further, immobilized invertase and cellulase showed good stabilities in repeating usage.
Ethanol production from starch by a coimmobilized mixed culture system of Aspergillus awamori and Zymomonas mobilis
Authors: Tanaka Hideo , Kurosawa Hiroshi , Murakami Hiroshi
Published: December 2004

The production of ethanol from starch by a coimmobilized mixed culture system of aerobic and anaerobic microorganisms in Ca‐alginate gel beads was investigated. The mold Aspergillus awamori was used as an aerobic amylolytic microorganism and an anaerobic bacterium, Zymomonas mobilis, as an ethanol producer. By controlling the mixing ratio of the microorganisms in the inoculum size, a desirable coimmobilized mixed culture system, in which the aerobic mycelia grew on and near the oxygen‐rich surface of the gel beads while the anaerobic bacterial cells mainly grew in the oxygen‐deficient central part of the gel beads, was naturally established under the aerobic culture conditions, and ethanol could be directly produced from starch by the system. The ethanol productivity by the system in flask culture was particularly affected by the shear stress (dependent on the shaking speed) which controlled the mycelial growth on the surface of the gel beads. Under optimum culture conditions in the flask culture, the glucose produced was instantly consumed, and was not observed in the culture broth; the final concentration of ethanol produced from 100 g/L starch was 25 g/L and the yield coefficient for ethanol, Ypls, was 0.38. The ethanol productivity by the coimmobilized mixed culture system was compared with those by other various culture systems and the advantages of the system were clarified.
The application of a novel heat flux calorimeter for studying growth of Escherichia coli W in aerobic batch culture
Authors: Marison I. W. , von Stockar U.
Published: December 2004

The modification and principle of a novel heat flux calorimeter for the in situ, on‐line measurement of the heat generated during microbial growth is described. Data concerning the physical characterization of the calorimeter as a fermentor, including stability and sensitivity of the heat signal, are presented. The calorimeter has been successfully applied to the study of the aerobic batch culture of Escherichia coli W on glucose under carbon and nitrogen limitation. A direct correlation between growth and heat evolution was obtained. Quantitative analysis of the data suggests that the new calorimetric technique could be used for monitoring growth and specific metabolic events, for convenient medium optimization, and as a basis for a novel fermentation process control system.
Coimmobilization of malate dehydrogenase and formate dehydrogenase in polyethyleneglycol(#4000)diacrylate gel by droplet gel‐entrapping method
Authors: Kajiwara S. , Maeda H.
Published: December 2004

A new immobilization technique suitable for coupled enzymes requiring cofactors was established. This is a droplet gel‐entrapping method in which many small droplets including the enzymes are fixed in the gel. The first emulsion was prepared by mixing of a solution containing thermostable malate dehydrogenase (MDH) and formate dehydrogenase (FDH) with benzene containing a surfactant. The first emulsion was added to a solution containing polyethyleneglycol(#4000)diacrylate and N,N′‐methylenebisacrylamide to prepare the second emulsion (w/o/w). After the second emulsion was gelled by addition of potassium persulfate and 3‐dimethylaminopropionitrile, the benzene was removed. The expressed MDH and FDH activities of the MDH–FDH immobilized gel were 7.1 and 13.9% of the initial activities, respectively. The Km values of the gel were 0.60mM for formate and 1.5μM for NAD, respectively. The Km for formate and NAD were found to be extremely low. By using the column packed with 30 g gel having the MDH activity of 41.7 units and the FDH activity of 11.1 units, 13.8mM oxalacetate was completely converted to malate at 30°C. The malate production rate was not affected by the concentration of more than 50mM formate, more than 2mM oxalacetate, and more than 0.1 mM NAD, respectively. Long‐term malate production was demonstrated at 30°C by passing the substrate solution containing the two substrates and NAD through the column. The maximum conversion ratio (7.8%) was obtained at the fifth day, and 83% of maximum productivity was maintained even after 3 weeks. The expressed FDH activity at the fifth day was calculated to be 20.5% of the initial activity.
A model for the filterability of activated sludge supported by mixed‐liquor biochemical data
Authors: Novak R. A.
Published: December 2004

A predictive model was developed to estimate the dewatering characteristics of waste‐activated sludges. This model utilizes the COD‐nitrogen ratio of the wastewater and the organic loading rate of the process to predict sludge filterability in terms of specific resistance. A completely mixed, continuous flow secondary treatment process with solids recycle was used for the cultivation of activated sludges. The sludge wasted from this process was used in Buchner funnel specific resistance determinations. The basic concepts involved in the development of the model were supported by sludge carbohydrate, protein, and surface charge data.
Production of penicillin in a fluidized‐bed bioreactor using a carrier‐supported mycelial growth
Authors: Kim J. H. , Oh D. K. , Park S. K. , Park Y. H. , Wallis D. A.
Published: December 2004

A carrier‐supported mycelial growth of Penicillium chrysogenum was applied to penicillin fermentation system using celite as a support material. Hyphal growth through the pore matrices of the material showed strong anchorages and provided highly stable biofilm growth. With bioparticles developed in such a manner, both cell growth and penicillin production were observed to increase significantly compared to the conventional dispersed filamentous cultures. Maximum values of specific penicillin production rate were found to be constant regardless of the growth form. A three‐phase fluidized‐bed fermentor was designed and tested for penicillin production using the bioparticles. Two modes of operation, semicontinuous and repeated fed batch, of the fermentor were tried. It was noted that the overgrowth of free mycelia and the development of fluffy loose bioparticles caused poor mixing and made the fermentor operation quite difficult. Control of the bioparticle size and the extension of production phase were therefore considered important to maintain the reactor productivity at a desired level. From the results of repeated fed‐batch operation it was found that the control of bioparticle size could be successfully achieved by phosphate‐limiting culture condition. Penicillin production under this condition was also observed to be maintained at a high level (about 80% of the maximum) for at least 1 month.
Pretreatment of wheat straw for fermentation to methane
Authors: Hashimoto Andrew G.
Published: December 2004

The effects of pretreating wheat straw with gamma‐ray irradiation, ammonium hydroxide, and sodium hydroxide on methane yield, fermentation rate constant, and loss of feedstock constituents were evaluated using laboratory‐scale batch fermentors. Results showed that methane yield increased as pretreatment alkali concentration increased, with the highest yield being 37% over untreated straw for the pretreatment consisting of sodium hydroxide dosage of 34 g OH−/kg volatile solids, at 90°C for 1 h. Gamma‐ray irradiation had no significant effect on methane yield. Alkaline pretreatment temperatures above 100°C caused a decrease in methane yield. After more than 100 days of fermentation, all of the hemi‐cellulose and more than 80% of the cellulose were degraded. The loss in cellulose and hemicellulose accounted for 100% of the volatile solids lost. No consistent effect of pretreatments on batch fermentation rates was noted. Semicontinuous fermentations of straw‐manure mixtures confirmed the relative effectiveness of sodium and ammonium‐hydroxide pretreatments.
Prevention of formation of acid drainage from high‐sulfur coal refuse by inhibition of iron‐ and sulfur‐oxidizing microorganisms. II. Inhibition in “run of mine” refuse under simulated field conditions
Authors: Dugan P. R.
Published: December 2004

The combination of sodium lauryl sulfate and benzoic acid effectively inhibits iron‐ and sulfur‐oxidizing bacteria in coal refuse and prevents the conversion of iron pyrite to sulfate, ferric iron, and sulfuric acid, thereby significantly reducing the formation of acidic drainage from coal refuse. The inhibitors were effective in a concentration of 1.1 mg/kg refuse, and data indicate that the SLS was in excess of the concentration required. The treatment was compatible with the use of lime for neutralization of acid present prior to inhibition of its formation.
Hydrolysis of dilute acid pretreated mixed hardwood and purified microcrystalline cellulose by cell‐free broth from Clostridium thermocellum
Authors: Lynd L. R. , Grethlein H. E.
Published: December 2004

The cellulase activity in cell‐free broths from the thermophilic, ethanol‐producing anaerobic bacterium Clostridium thermocellum is examined on both dilute‐acid‐pretreated mixed hardwood (90% maple, 10% birch) and Avicel. Experiments were conducted in vitro in order to distinguish properties of the cellulase from properties of the organism and to evaluate the effectiveness of C. thermocellum cellulase in the hydrolysis of a naturally occurring, lignin‐containing substrate. The results obtained establish that essentially quantitative hydrolysis of cellulose from pretreated mixed hardwood is possible using this enzyme system. Pretreatment with 1% H2SO4 and a 9‐s residence time at 220, 210, 200, and 180°C allowed yields after enzymatic hydrolysis (percentage of glucan solubilized/ glucan potentially solubilized) of 97.8, 86.1, 82.0, and 34.6%, respectively. Enzymatic hydrolysis of mixed hardwood with no pretreatment resulted in a yield of 10.1%. Hydrolysis yields of >95% were obtained from ∼0.6 g/L mixed hardwood pretreated at 220°C in 7 h at broth strengths of 60 and 80% (v/v) and in approximately 48 h with 33% broth. Hydrolysis of pretreated mixed hardwood is compared to hydrolysis of Avicel, a pure microcrystalline cellulose studied previously. The initial rate of Avicel hydrolysis saturates with respect to enzyme, whereas the initial rate of hydrolysis of pretreated wood is proportional to the amount of enzyme present. Initial hydrolysis rates for pretreated wood and Avicel at 0.6 g/L are greater for wood at low broth dilutions (1.25: 1 to 5 :1) by up to 2.7‐fold and greater for Avicel at high broth dilutions (5 : 1 to 50 : 1) by up to 4.3‐fold. Maximum rates of hydrolysis are achieved at <2 g substrate/L for both pretreated wood and Avicel. The substrate concentration at one‐half the maximum observed rate for C. thermocellum broths is smaller for pretreated mixed hardwood than for Avicel and decreases with increasing broth dilution for both substrates. An initial activity per volume broth of approximately 11 μmol soluble glucose equivalent produced/L broth/min is observed for mixed hardwood pretreated at 220°C and for Avicel at high broth dilutions; the initial activity per volume broth for Avicel is lower at low broth dilutions. The results indicate that pretreated wood is hydrolyzed at rates comparable to Avicel under many conditions and at rates significantly faster than Avicel under several conditions.
Cellulase immobilized on poly‐L‐glutamic acid
Authors: Takeuchi Tamio , Makino Keisuke
Published: December 2004

Cellulase (Cellulosin AC‐8) was immobilized on poly‐L‐glutamic acid. This immobilized cellulase (IC) is water soluble in the neutral and alkaline solutions, where IC has the activity, while IC can be made insoluble by lowering the pH so that it can be recovered from the reaction mixture with its activity. The optimum pH and temperature were determined to be 5.5 and 55°C, respectively. The stability of IC against change in the pH and temperature was improved by the immobilization. Solvolysis of 3N‐NaOH‐treated cellulose, with IC under the optimum conditions found here, led to the production of low‐molecular‐weight compounds.
Modeling and static optimization of the ethanol production in a cascade reactor. II. Static optimization
Authors: Dourado A. , Calvet J. L. , Sevely Y. , Goma G.
Published: December 2004

In Part I1 of this research a complex model was obtained for describing the ethanol fermentation in a cascade reactor. This complexity is due to both the nonlinearity and the large scale representation. Based on techniques of partitioning and relaxation, a decentralized successive approximation method is developed for static optimization. The influence of the way of fermentation during continuous culture in multistage fermentors is studied in the case of a double inhibition of cell growth and product formation by both substrate and final product. The optimal number of reactors is discussed with respect to the strength of the ethanol inhibition, while the interest of head feeding or distributed feeding is evaluated in relation to the strength of substrate inhibition.
Chronocoulometric techniques in the study of computerized enzyme electrode systems
Authors: Rishpon J.
Published: December 2004

The electrochemical transient of a two‐substrate enzyme electrode was studied theoretically and experimentally. Operation of such electrodes in the chronocoulometric mode leads to increased electrode sensitivity and makes possible the retrieval of useful information on transport and kinetics parameters. Digital simulation was used to solve the kinetics and transport equations and to produce the theoretical chronocoulometric response. A glucose electrode based on glucose oxidase crosslinked to different matrices was tested with air oxygen and p‐benzoquinone as the cosubstrate. A computerized electrochemical system was employed for electrode potential control and data acquistion and analysis.
Oxidation of hydrogen sulfide by Thiobacillus denitrificans: Desulfurization of natural gas
Authors: Sublette Kerry L. , Sylvester Nicholas D.
Published: December 2004

It has been demonstrated that Thiobacillus denitrificans may be readily cultivated anaerobically in batch reactors on H2S (g) under sulfide‐limiting conditions. Under these conditions sulfide concentrations in the culture medium were less than 1 μM, resulting in very low concentrations of H2S in the reactor outlet gas. The stoichiometry of the reaction was determined, and stable reactor operation was demonstrated at reactor loadings as high as 4–5 mmol H2S oxidized/h g biomass. Maximum loading was estimated at 5.4–7.6 mmol H2S/h g biomass under the conditions employed in this study. Indicators of reactor upset were determined and recovery from upset conditions demonstrated. Barotolerance of T. denitrificans to 12.5 MPa as well as a relative insensitivity to pressurization–depressurization cycles were also demonstrated. T. denitrificans was observed to be very sensitive to CH3SH but relatively tolerant of CS2, COS, and CH3SCH3.
Modeling bisubstrate removal by biofilms
Authors: Namkung Eun , Rittmann Bruce E.
Published: December 2004

A bisubstrate secondary utilization model is based on the concept that an individual substrate can be utilized not only by the biomass by its utilization but also by the biomass made from the utilization of the other substrate. When substrate concentrations are low, a key factor is having sufficient substrate to initiate biofilm growth. Modeling results for three characteristic cases demonstrate that satisfying a total Smin concentration for a bisubstrate system is the necessary condition for initiating biofilm growth and simultaneous utilization of both substrates. Because having more than one substrate supporting biofilm growth enhances the removal of each compound, the utilization rate of a specific compound can be increased by the concentration of other compounds, and the total Smin concentration can be less than the weighted average of individual Smin values.
Energetic analysis of the growth of Methanobrevibacter arboriphilus A2 in hydrogen‐limited continuous cultures
Authors: Morii Hiroyuki , Koga Yosuke , Nagai Shiro
Published: December 2004

Hydrogen‐limited chemostat cultures of Methanobrevibacter arboriphilus A2 were carried out. The available electron balance and carbon balance in M. arboriphilus A2 and other methanogenic strains grown on various substrates were well satisfied. This indicates that no extracellular organic products were formed during methanogenic growth. The molar growth yields for methane (Y) were calculated as 1.06–1.42 g cell/mol CH4 at dilution rate (0.21–0.43 day−1). The smaller Y of M. arboriphilus A2 compared with that of the other methanogenic strains was probably owing to the low growth rate of M. arboriphilus A2. The low value of Y may be favorable for methane fermentation because less sludge accumulation is expected. The efficiency of free energy transduction to ATP during methane formation from H2 + CO2 was 12–17% at the dilution rate (0.21–0.43 day−1) assuming that YATP was 6.5 g/mol and the free energy change of CO2 reduction to methane with H2 was −62.8 kJ/mol under physiological conditions.
The effect of pH and lactose concentration on solvent production from whey permeate using Clostridium acetobutylicum
Authors: Ennis B. M. , Maddox I. S.
Published: December 2004

A study was performed to optimize the production of solvents from whey permeate in batch fermentation using Clostridium acetobutylicum P262. Fermentations performed at relatively low pH values resulted in high solvent yields and productivities, but lactose utilization was incomplete. At higher pH values, lactose utilization was improved but acid production dominated over solvent production. When operating at the higher pH values, an increase in the initial lactose concentration of the whey permeate resulted in lower rates of lactose utilization, and this was accompanied by increased solvent production and decreased acid production. Analysis of data from several experiments revealed a strong inverse relationship between solvent yield and lactose utilization rate. Thus, conditions which minimize the lactose utilization rate, such as low culture pH values or high initial lactose concentrations, favor solventogenesis at the expense of acid production.
Low‐pressure airlift fermenter for single cell protein production: I. Design and oxygen transfer studies
Authors: Chen N. Y. , Kondis E. F. , Srinivasan S.
Published: December 2004

The energy consumption of a fermenter constitutes a major part of the operating expense of a single cell protein process. A low‐pressure airlift fermenter was designed to reduce this cost. In this new design, the fermenter broth is kept below 120 cm in depth, and air alone is employed to fulfill the need of supplying oxygen, and cooling and agitating the broth. The use of low‐pressure air from air blowers instead of air compressors lowers the capital cost of air delivery and reduces the energy consumption in the fermenter section to below 1 kWh/kg protein, a saving of over 70% as compared to a conventional stirred tank fermenter. It also eliminates the investment of mechanical agitators, heat exchangers, and air compressors. Sulfite oxidation studies confirmed the design concepts.
Physicochemical factors affecting ethanol adsorption by activated carbon
Authors: Bradley K. J. , Hamdy M. K. , Toledo R. T.
Published: December 2004

Powder and granular activated charcoal were evaluated for ethanol adsorptivity from aqueous mixtures using an adsorption isotherm. Ethanol adsorption capacity was more pronounced at 25°C as compared to 5, 15, and 40°C. When pH of the ethanol–buffer mixture (0.09 ionic strength) was changed from acidic (2.3) to neutral and then to alkaline (11.2), ethanol adsorption was decreased. Increasing ionic strength of the ethanol‐buffer mixtures from 0.05 to 0.09 enhanced ethanol adsorption but a further increase to 0.14 showed no significant effect. Ethanol adsorption was more efficient from an aqueous ethanol mixture as compared to semidefined and nondefined fermentation worts, respectively. Heating granular charcoal to 400°C for 1 h and 600°C for 3 h in N2 increased ethanol adsorptivity and heating to 1000°C (1 h) in CO2 decreased it when ethanol was removed from dilute solutions by simple pass adsorption in a carbon packed column. Granular charcoal was superior to powdered charcoal and an inverse relationship was noted between the weight of the granular carbon bed in the column and ethanol adsorbed/g carbon. Decreasing the column feed flow rate from 7.5 to 2.0 L aqueous ethanol/min increased the adsorption rate.
Evaluation of Escherichia coli and Candida utilis as a model continuous, competitive mixed culture system
Authors: Goochee Charles F. , Hatch Randolph T. , Cadman Theodore W.
Published: December 2004

The yeast Candida utilis and the bacterium Escherichia coli B/r were evaluated as a candidate experimental, continous, competitive mixed culture system under ammonia–nitrogen limited conditions at 30°C. High dilution rates favored yeast dominance, while low dilution rates favored bacterial dominance. The hydrogen ion concentration was also demonstrated to be an effective manipulative variable for control of the yeast–bacterial mixed culture. Through trial‐and‐error manipulation of the pH for the mixed culture operating at constant dilution rate, it was possible to locate a metastable equilibrium point and to operate in the vicinity of that point for more than 24h. The reproducible emergence of a variant E. coli was also noted in this study.
Effect of a broad‐host range plasmid on growth dynamics of Escherichia coli and Pseudomonas putida
Authors: De Bernardez Eliana R. , Dhurjati Prasad S.
Published: December 2004

Host–plasmid interactions were studied for the broad‐host range plasmid, pTJS26, a derivative of RK2. To isolate host and plasmid contributions to the growth dynamics and plasmid stability, separate experiments were performed with host and recombinant cells for two different gram‐negative hosts, Pseudomonas putida and Escherichia coli, at two different temperatures, 30 and 37°C. At the lower temperature (30°C) the growth kinetics were not affected by the plasmid, but plasmid instability was observed. At the higher temperature (37°C) growth rates and yields were lower than that for the hosts, but the plasmid was stable. This behavior can be explained by a combination of two phenomena. First, the copy number control mechanism may be temperature sensitive and, second, plasmid segregation may be inefficient. For both E. coli and P. putida the growth dynamics of the recombinant system was dictated by the presence of the plasmid.
Evaluation of organosolv processes for the fractionation and modification of corn stover for bioconversion
Authors: Lee Yong‐Hyun , Robinson Campbell W. , Moo‐Young M.
Published: December 2004

Corn stover was pretreated for compositional fractionation and structural modification for maximum conversion of carbohydrate to soluble sugars. The process scheme consisted of three steps: (1) mild prehydrolysis in dilute sulfuric acid, (2) delignification with various organosolv solvents, and (3) enzymatic hydrolysis in an agitated bead reactor. Prehydrolysis of corn stover can be achieved at temperatures ranging from 95 to 120°C, which is a much milder condition than must be applied to wood. Various organosolv solvents, including several alcohols with acid as catalyst, ethylene glycol, and its derivatives, and amines were used for delignification of the prehydrolyzed corn stover. Aromatic alcohols were found to be more effective in solubilizing the prehydrolyzed corn stover than were the aliphatic alcohols. Butanol was the most effective among the aliphatic alcohols; on the other hand, phenol was the best among the aromatic alcohols. Ethylene glycol, methylcellosolv, and ethylcellosolv were effective in solubilizing the prehydrolyzed corn stover but not for enhancing the enzymatic hydrolysis. Various amines achieved delignification at the mild temperature of 95°C, but they tended to solubilize substantial amounts of carbohydrate in addition to lignin. n‐Butylamine was effective in enhancing the conversion during enzymatic hydrolysis; it was a good delignifying agent as well as one that achieved a concomitant swelling of the cellulose structure. The low enzymic conversion (20–37%) of prehydrolyzed and solvent‐extracted corn stover that was achieved implies that lignin is not the only major barrier for enzymatic hydrolysis. Modification of cellulose structure also should be accomplished to achieve a high degree of conversion. Enzymatic hydrolysis in the agitated bead system increased the rate and extent of conversion of corn stover substantially compared to systems without beads.
Coexistence of bacteria and feeding ciliates: Growth of bacteria on autochthonous substrates as a stabilizing factor for coexistence
Authors: Sambanis A. , Pavlou S. , Fredrickson A. G.
Published: December 2004

There is good evidence that the specific feeding and growth rates of a population of suspension‐feeding ciliates on a population of bacteria is described by the classic Monod model or something very like it. However, use of this model combined with the assumption that feeding of the ciliates is the only interaction between the populations leads to predictions grossly at variance with experimental observations. A second interaction between the populations, growth of the bacteria on products of lysis, and perhaps metabolism of the ciliates is known to occur and might be an important factor in determining the dynamics of ciliate–bacterial systems. Whether or not this is the case is examined in the present article. It is concluded that accounting for the second interaction does not remove the discrepancies between model predictions and experimental observations. It is concluded also that the second interaction is likely not important except in batchtype situations where the supply of available energy for supporting biological activity is not replenished.
Alcohol fermentation of corn starch digested by Chalara paradoxa amylase without cooking
Authors: Mikuni Katsuhiko , Monma Mitsuru , Kainuma Keiji
Published: December 2004

Alcohol fermentation of corn starch without cooking was performed by using Chalara paradoxa glucoamylase preparation, which had stronger raw starch digesting activity than those of the conventionally known glucoamylases. A raw corn starch–enzyme–yeast mixture was fermented optimally at pH 5.0 and 30°C for five days and produced ethanol. The yields of ethanol were between 63.5 and 86.8% of the theoretical value by baker's yeast (Saccharomyces cerevisiae), and between 81.1 and 92.1% of the theoretical value by sake yeast (Saccharomyces sake).
Purification of an extracellular cellulose‐binding endoglucanase of Cellulomonas sp. ATCC 21399 by affinity chromatography on H3PO4‐swollen cellulose
Authors: Poulsen Otto M. , Petersen Lars W.
Published: December 2004

A cellulose‐binding endoglucanase (endoglucanase A) of Cellulomonas sp. ATCC 21399 was purified to immunological homogeneity by affinity chromatography ob H3PO4‐swollen cellulose. This method of purification turned out to be an easy and very gentle method for obtaining a high yield of cellulose‐binding endoglucanase. The purified enzyme was immunologically homogeneous but appeared heterogeneous when analyzed by denaturing polyacrylamide gel electrophoresis. In addition to the cellulose‐binding of endoglucanase A, the enzyme also had a strong affinity for Concanavaline A, indicating that the enzyme was glycosylated. Purified endoglucanase A showed an endo mode of action on carboxymethylcellulose. The enzyme could hydrolyze microcrystalline cellulose when acting alone, and the enzyme had a high specific activity on H3PO4‐swollen cellulose.
Investigation of plasmid instability in amylase‐producing B. subtilis using continuous culture
Authors: Kadam Kiran L. , Wollweber Karen L. , Grosch Josephine C. , Jao Yun C.
Published: December 2004

Continuous culture was employed to study plasmid instability in an amylase‐producing Bacillus subtilis 1A289 that was genetically manipulated. No true steady state could be obtained with 1A289(pEAA)‐strain (plasmid)‐due to its structural instability, which occurred both with glucose and Maltrin‐100 as limiting carbon sources. The plasmid, pEAA (CmR, amy+, i.e., chloramphenicol resistant, amylase positive) degenerated into a smaller plasmid, pEAA1 (CMR, amy−) that was stable. There was a direct correlation between amylase‐producing ability and this structural instability since famy (fraction of cells with amylase‐producing ability) reached zero at the same time that f (fraction of cells that are resistant to chloramphenicol) reached its maximum level. Since the deletion in pEAA was larger than the original amylase‐gene insert, either all of part of the insert is absent from pEAA1. Though on discernible change in 1A289(pHV33), where pHV33 is the vector plasmid, was observed during continuous cultivation, its behavior was different from that of the stable 1A289(pEAA1).
Isolation and purification of protease from human placenta by foam fractionation
Authors: Sarkar P. , Bhattacharya P. , Mukherjea R. N. , Mukherjea M.
Published: December 2004

The effect of operating parameters like pH, protein concentration, column geometry, and gas flow rate on the separation efficiency of proteolytic enzymes from crude human placental homogenate has been studied in a batch foam column. Purification has been found to be optimum at pH 8.0, close to the isoelectric pH, at which the surface adsorption of the protein on the foam bubbles is maximum. Both purification and recovery varied significantly with total protein concentration. Stable bubble formation was hindered at lower protein concentrations, while extraneous proteins rather than the protease were preferentially adsorbed at higher protein concentrations, decreasing the purification efficiency. Column diameter and column height should be optimized for any specific feed protein concentration and gas flow rate. However, the enrichment ratio was found to decrease with the increase in flow rate. The results indicate that foam fractionation is an effective separation process for recovering valuable biochemicals from biological materials.
A simple Na2SO3 feeding method for KLa measurement in large‐scale fermentors
Authors: Imai Yasuhiko , Takei Hirosuke , Matsumura Masatoshi
Published: December 2004

A simple and convenient method for measuring KLa in large‐scale fermentors was proposed. This method was based on the measurement of the dissolved oxygen concentration under steady state conditions established by an equivalency of the sulfite ion feed and chemical oxidation rates. This method had the following advantages: It was a steady state method, and so it was not necessary to consider the response lag of a dissolved oxygen probe and the response lag due to gas phase mixing in fermentors. The oxygen content of the effluent gas in this measuring system was nearly the same as that of the sparged air. Therefore, it was possible to use the oxygen partial pressure of the sparged air for the calculation of the driving force of oxygen transfer. The detailed information on the kinetics of sulfite oxidation was not necessary, because the dissolved oxygen concentration in steady state was not influenced by sulfite oxidation rates. The KLa measurement was finished in as short a period as 150 s, even in a fermentor with a volume of 10 m3. Since the amount of Na2SO4 accumulation in the test fermentors was very small because of the quick measurement, the KLa values obtained by this method were applicable to the electrolyte‐free system. Furthermore, we could discharge the used liquid from the fermentors into a drain without any pretreatment due to the low salt concentration.