bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanistically detailed model of cellular metabolism for glucose‐limited growth of Escherichia coli B/r‐A
Authors: Peretti Steven W. , Bailey James E.
Published: December 2004

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

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

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

Cellulase produced by fungus Trichoderma viride was immobilized on agarose beads (Sepharose 4B) activated by cyanogen bromide and also on activated agarose beads that contained spacer arm (activated CH‐Sepharose 4B and Affi‐Gel 15). The CMCase activity retained by immobilized cellulase on activated Sepharose containing the spacer tended to be higher than that immobilized without spacer, although the extent of protein immobilization was lower. Also, the higher substrate specificity for cellulase immobilized on beads with spacer was obtained for cellobiose, acid‐swollen cellulose, or cellulose powder. The hydrolysis product from their substrates was mainly glucose.
Hydrodynamic effects on animal cells grown in microcarrier cultures
Authors: Croughan Matthew Shane , Hamel Jean‐Francois , Wang Daniel I. C.
Published: December 2004

Hydrodynamic phenomena in microcarrier cultures are investigated with regard to the development of improved reactor designs for large‐scale operations. New concepts and theoretical models that describe new data as well as previously published data are presented.
Modeling and static optimization of the ethanol production in a cascade reactor. I. Modeling
Authors: Dourado A. , Goma G. , Albuquerque U. , Sevely Y.
Published: December 2004

Let us consider the modeling of a cascade reactor for the production of ethanol. The rates of reaction in alcoholic fermentation are modeled so that it can assume both ethanol and substrate inhibition, in relation to the observed results.

A nonstructured model, based on biomass, substrate, and ethanol concentrations, is developed and identified. It is a complex model, this being due to the nonlinearity between the specific rate of ethanol production and the growth rate and, on the other hand, the study of the static optimization of ethanol fermentation is performed.
Generalization of monod kinetics for analysis of growth data with substrate inhibition
Authors: Luong J. H. T.
Published: December 2004

The inhibitory effect of butanol on yeast growth has been studied for the strain Candida utilis ATCC 8205 growing aerobically on butanol under batch conditions. A mathematical expression was then proposed to fit the kinetic pattern of butanol inhibition on the specific growth rate:

The maximum allowable butanol concentration above which cells do not grow was predicted to be 9.16g/L. The proposed model appears to accurately represent the experimental data obtained in this study and the literature data developed for a variety of batch culture systems at widely ranging substrate concentrations.
Simulations of host–plasmid interactions in Escherichia coli: Copy number, promoter strength, and ribosome binding site strength effects on metabolic activity and plasmid gene expression
Authors: Peretti Steven W. , Bailey James E.
Published: December 2004

A mechanistically detailed single‐cell model E. coli B/r‐A was adapted to simulate the effects of vector presence on cell metabolism. Competition for RNA polymerase between chromosome and plasmid DNA is explicitly included. Distribution of active ribosomes among chromosome‐ and plasmid‐derived messenger RNA, another key facet of host–plasmid interactions, is also treated in detail. Simulations of recombinant cell growth rate and cloned‐gene productivity as a function of relative plasmid number per cell agree closely with experimental results. Model prediction of the variation of cell cycle parameters C and D with plasmid number are roughly consistent with available data. Models of this class can be used to simulate changes in productivity resulting from specific alterations in the expression vector. The effects of changing cloned‐gene promoter and ribosome binding strengths and of augmenting cell transcription or translation capacity have been studied using the recombinant cell model. Results suggest that cloned‐gene expression is limited by cellular transcription capacity. These and other parametric studies, conveniently implemented using the computer cell, provide important guidance for future experiments directed at better understanding of host–plasmid interactions and at optimizing recombinant system productivity.
The dehydration of fermentative 2,3‐butanediol into methyl ethyl ketone
Authors: Tran Ai V. , Chambers Robert P.
Published: December 2004

A solid acid catalyst consisted of sulfonic groups covalently bound to an inorganic matrice was developed to dehydrate 2,3‐butanediol into methyl ethyl ketone. Rate constant and apparent activation energy of the dehydration reaction were determined. The decay course of the catalyst was a two‐stage curve. The catalyst was deactivated more rapidly in the first stage than in the second stage. The strategy of maintaining constant degree of dehydration was employed to lengthen the lifetime of catalyst. Treatment of the 2,3‐butanediol containing fermentation broth with activated carbon greatly facilitated the subsequent dehydration reaction.
Theoretical and experimental yields for photoautotrophic, mixotrophic, and photoheterotrophic growth
Authors: Lee H. Y. , Erickson L. E.
Published: December 2004

Available electron methods are presented and used to estimate theoretical energetic growth yields for photoautotrophic, mixotrophic, and photoheterotrophic growth of algae and photosynthetic bacteria. The theoretical yields are compared to experimental values reported previously. For photoautotrophic and mixotrophic growth of algae experimental values that approach and even exceed the theoretical values have been reported in the literature. For photosynthetic bacteria experimental yields are much smaller than thetheoretical maximum values.
Kinetics of milk coagulation: II. Kinetics of the secondary phase: Micelle flocculation
Authors: Carlson Alfred , Hill Charles G. , Olson Norman F.
Published: December 2004

A kinetic model for the agglomeration of milk micelles following κ‐casein hydrolysis is described. The key features of the model are: (1) the surface potential of casein micelles is sufficient to explain the colloidal stability of the milk system; (2) the reduction in surface potential following κ‐casein hydrolysis explains the loss of stability; (3) partial hydrolysis leads to limited agglomeration; and (4) the kinetics of agglomeration are compatible with the theory that completely hydrolyzed micelles have only a limited number of interaction sites. The model accurately predicts solution turbidity increase assuming that micelles have only circa 1.2 interaction sites on the average under the experimental conditions of this study.
The kinetics of milk coagulation: IV. The kinetics of the gel‐firming process
Authors: Carlson Alfred , Hill Charles G. , Olson Norman F.
Published: December 2004

A mechanistic kinetic model of gel firmness development during milk gel formation is presented. The model correctly accounts for the influence of enzymatic κ‐casein hydrolysis on the rate of firmness development in renneted milk gels. The model used is based on two first‐order reactions occurring in series. The first reaction is enzymatically controlled and corresponds to the formation of gel crosslink sites by κ‐casein hydrolysis. The second reaction is nonenzymatic and corresponds to the process of crosslink formation and depletion of active sites. The model successfully predicts gel firmness development in the temperature range 31–45°C for a variety of initial enzyme concentrations.
Growth inhibitory and lethal effects of ethanol on Escherichia coli
Authors: Sawada Tatsuro , Nakamura Yoshitoshi
Published: December 2004

The growth inhibitory and lethal effects of ethanol on Escherichia coli BB were investigated in batch cultures, by measuring total cell number, viable cell number, and cell mass concentration. Ethanol below ca. 50 g/L allowed exponential growth but depressed the specific growth rate. The effect of ethanol on the specific growth rate appeared to follow noncompetitive inhibition kinetics with apparently cooperative binding with a Hill coefficient of 2.5. The Hill coefficient and the inhibition constant were temperature independent over the range tested. Ethanol at 30 g/L decreased the growth yield. Ethanol enhanced the specific death rate in an experimental way. Stationary cell populations were more resistant than exponential ones but the degree of enhancement by ethanol was the same in both populations. Isopropanol and propanol also enhanced the specific death rate exponentially and the degree of enhancement was correlatedwith their membrane–buffer partition coefficients.
Preparation and properties of soluble–insoluble immobilized proteases
Authors: Fujimura Motoki , Mori Takao , Tosa Tetsuya
Published: December 2004

In order to carry out an effective enzyme reaction, the preparation of soluble–insoluble immobilized enzyme was investigated. Proteases were selected as model enzymes, and their immobilization was carried out by using an enteric coating polymer as a carrier. Among the polymers tested, methacrylic acid–methylacrylate–methylmethacrylate copolymer (MPM‐06) gave the most active soluble–insoluble immobilized papain. This immobilized papain showed insoluble from below pH 4.8 and soluble form above pH 5.8; it was also soluble in water‐miscible organic solvent. It was reusable and more stable with heat and water‐miscible organic solvents than native proteases. Furthermore, various proteases could be immobilized by using MPM‐06 with high activity. Chymotrypsin immobilized by this method catalyzed the effective peptide synthesis in a heterogeneous reaction system containing water‐miscible organic solvent.
Isolation of a respiratory‐deficient Kluyveromyces fragilis mutant for the production of ethanol from Jerusalem artichoke
Authors: Guiraud Joseph P. , Bourgi Jamal , Stervinou Michèle , Claisse Maurice , Galzy Pierre
Published: December 2004

A respiratory‐deficient, mutant of Kluyveromyces fragilis was isolated using a ethidium bromide mutagenesis. It was characterized by a loss of cytochromes a + a3 and by an improvement of its inulinase activity. Under anaerobic conditions this mutant was always better than the wild strain for ethanol production especially from Jerusalem artichoke extracts containing large amounts of high polyfructosans ("early" extracts).
Properties and quality characteristics of rennin extracted by ultrasound
Authors: Zayas Joseph F.
Published: December 2004

An optimal time of 45 min was established for extraction of rennin (chymosin) from abomasa using ultrasound. Effect of swelling of raw material and increased temperature of extraction medium (45°C) was established. As rennin is resistant to ultrasound treatment and enhanced temperatures, ultrasound extraction results in a significant increase in the yield and activity. However, purified rennins were sensitive to ultrasound action. There were found changes of the electrophoretic properties and amino acid composition. Physicochemical properties were different and quality characteristics were higher for ultrasonic extracted rennin than for the control, particularly specific clotting activity, proteolytic activity, and rheological properties of curd. However, nonspecific proteolysis, coefficient of rennin effectivity, appearance, odor, solubility, moisture, protein, and NaCI content were similar. Ultrasonic extraction caused a decrease in the total viable counts of microorganisms of rennin, because of the short time of extraction.
Invertase activity of intact cells of Saccharomyces cerevisiae growing on sugarcane molasses. II. Unsteady‐state continuous‐culture tests
Authors: Vitolo Michele , Vairo Marina L. R. , Borzani Walter
Published: December 2004

During unsteady‐state continuous culture of Saccharomyces cerevisiae on sugarcane blackstrap molasses, the invertase activity of the intact yeast cells oscillated. Disturbances were produced by changing medium composition, air rate, impeller speed, and dilution rate. The influence of the oxygen supply rate and of the dilution rate on the invertase activity depend on the medium composition. The highest invertase activity was obtained when, after a steady‐state attained using unsupplemented culture medium, nutrients were added to the feeding mash. A Monod‐like equation seems to be the best representation of the correlation between the specific rate of reducing sugars consumption and the specific rate of nonreducing sugar hydrolysis by the yeast cells.
Modelling mass transfer and agitator performance in multiturbine fermentors
Authors: Bader Fredric G.
Published: December 2004

A methodology for mathematically analyzing agitator performance and mass transfer in large multiturbine production fermentors is presented. The application of this approach provides a method for determining axial dissolved oxygen profiles under conditions of known mass transfer rates as a function of agitation–aeration characteristics. A stagewise approach is used which divides the fermentor into a series of mixing cells. This allows for each turbine and mixing cell to be individually optimized. The model also permits the determination of the mass transfer coefficient for each turbine based upon limited dissolved oxygen data. The primary limitation of this approach rests in the limited data and correlations available for multiturbine systems. The structure of the modelling approach can serve as a basis for testing single turbine correlations and adapting them to multiturbine systems. The step‐by‐step details of the mathematical analysis are presented and interpreted. A series of computer simulations demonstrate the effect of typical fermentor operating variables on the axial dissolved oxygen profile. Further simulations demonstrate the effect of modifying agitator blade numbers on the dissolved oxygen profile and agitator power requirement.
Acidogenic fermentation of lactose
Authors: Kisaalita W. S. , Pinder K. L. , Lo K. V.
Published: December 2004

Cheese whey is the main component of waste streams from cheese manufacturing plants. Whey is a high biochemical oxygen demand (BOD) effluent that must be reduced before the streams are sent to the sewer. It is proposed in this article that the production of methane by anaerobic fermentation would be the best use of this stream, especially for small plants. Single‐stage fermentation of lactose, the main component of whey, results in a very low pH and a stalled process. Two‐phase fermentation will eliminate this problem. The acidogenic stage of fermentation has been studied at pH of between 4 and 6.5. The nature of the main products of the reaction have been found to be pH dependent. Below a pH of 4.5 a gas (CO2 and H2) is produced along with ethanol, acetate, and butyrate. Above a pH of 4.5 no gas was produced, and the liquid products included less ethanol and butyrate and more acetate. A separate study on the conditions for gas formation showed that if the pH dropped for a short time below 4.5 gases were formed at all subsequent pH. This would indicate a change in population distribution due to the period at a low pH. By assuming that the desired products from the acidogenic stage were butyrate, acetate, and no gases, the optimum pH range was found to be between 6.0 and 6.5.
The use of rotifers for the maintenance of monoalgal mass cultures of Spirulina
Authors: Mitchell S. A. , Richmond A.
Published: December 2004

Zooplankton was successfully used for the biological control of unicellular algal contaminants in Spirulina mass cultures even under conditions adverse to the growth of Spirulina (maximal winter daily temperature of approximately 10°C and very low bicarbonate concentration). Brachionus plicatilis (Rotifera) was the most successful species of zooplankton used. The interrelationships between Spirulina, green unicellular contaminant, and B. plicatilis were studied under various conditions. Two species of unicellular contaminant were used; Monoraphidium minutum was isolated from local cultures and Chlorella vulgaris, obtained from contaminated Spirulina cultures in Israel. The rotifer B. plicatilis successfully controlled the population size of both contaminants whether they were introduced in a single addition or as a daily dose. The biological control of the unicellular contaminants allows Spirulina to be cultured in a medium low in bicarbonate, thereby reducing the cost of the medium and increasing the quantity of CO2 that may be freely absorbed from the atmosphere at the optimal pH for Spirulina cultivation.
Studies on a wild strain of Schizophyllum commune: Cellulase and xylanase production and formation of the extracellular polysaccharide Schizophyllan
Authors: Steiner W. , Lafferty R. M. , Gomes I. , Esterbauer H.
Published: December 2004

A wild strain of schizophyllum commune (Fr:Fr:) isolated in Bangladesh produced cellulase and xyianase in high yields as well as the exobiopolymer schizophyllan. It was found experimentally that concentrations of 4% Avicel, 3.5% peptone, and 0.5% Ca(NO3)2·4H2O were optimal for growth and product formation. Bacto‐peptone was found to be the most suitable substrate of a number of casein, mycological, and meat peptone preparations for enzyme production. Young plate‐culture inocula (4 days) were found to be better than comparatively aged fungal cultures (14 days). With the optimized medium, 5 units filter paper (FP) cellulase, 1244 units xylanase, 108 units β‐glucosidase, and 65 units of carboxymethyl (CM) cellulase per mL culture filtrate were obtained in shake flasks. In a laboratory fermentor the respective enzyme activities were 4.5 units FP‐cellulase, 1200 units xylanase, 100 units β‐glucosidase, and 60 units CM‐cellulase per mL culture filtrate. A biopolymer, reported to be active against can cerous cells, was an additional product in addition to the enzymes.
Unsteady‐state operation of continuous fermentor for enhancement of cell mass production
Authors: Hong Juan , Lee C. K.
Published: December 2004

The transient behavior of continuous fermentation is studied concentrating on the time scale intrinsic to the system. The time scale is the time required for the fermentorto reach a stable steady state after the disturbance of cell mass is introduced. When the cell concentration is disturbed from the steady‐state value, in particular, at the dilution rate near washout, the transient period becomes extended significantly, and the steady state is resumed sluggishly. This sluggish transient behavior could be turned to an advantage for enhancing the cell mass output rate. The proposed transient operation is a continuous fermentation whereby a positive disturbance in the cell mass is introduced, so that the cell concentration is higher than the steady‐state value for an extended transient period. It is shown that a significantly higher cell mass production than that from the steady‐state continuous fermentation can be achieved. Simple experiments were performed to demonstrate the improvement of cell (Candida utilis) productivity.
Immobilization of microorganisms by adhesion: Interplay of electrostatic and nonelectrostatic interactions
Authors: Mozes N. , Marchal F. , Hermesse M. P. , Van Haecht J. L. , Reuliaux L. , Leonard A. J. , Rouxhet P. G.
Published: December 2004

The adhesion of three microorganisms (Saccharomyces cerevisiae, Acetobacter aceti, and Moniliella pollinis) to different materials has been studied using various supports (glass, metals, plastics), some of which were treated by an Fe(III) solution. The surface properties of the cells were characterized by the zeta potential and an index of hydrophobicity; characterization of the supports involved surface chemical analysis (XPS) and contact angle measurements. Cell suspensions in pure water at a given pH were left to settle on plates; the latter were then rinsed and examined microscopically, Saccharomyces cerevisiae and A. aceti adhere to metals under certain pH conditions but do not adhere to any of the other materials tested unless it is previously treated by ferric ions; adhesion of these hydrophilic cells is essentially controlled by electrostatic interactions. Moniliella pollinis adhere spontaneously to glass and to polymeric materials, but its attachment is also influenced by cell–cell or cell–support electrostatic repulsions; near the cell isoelectric point, cell flocculation is competing with adhesion to a support.
Enzyme‐Entrapping behaviors in alginate fibers and their papers
Authors: Kobayashi Yoshinari , Matsuo Ryûkichi , Ohya Takaichi , Yokoi Nobumasa
Published: December 2004

Enzyme immobilization in the form of fiber and paper was easily achieved by wet spinning of aqueous admixture of sodium alginate and enzymes into divalent metallic ion solution as a coagulating bath, followed by paper making of resultant shortly cut fibers. Entrapment yields of enzymes used, e.g., glucoamylase, cyclodextrin glucanotransferase, endo‐polygalacturonase, and protease, were always higher in calcium alginate fibers and their papers than those in corresponding beads. It was found that the yields increased with an increase of the discharge rate through the spinning nozzle because the higher discharge rate could provide more highly oriented metal‐chelate linear polymer molecules along the fiber axis for preventing leakage of entrapped enzymes. Divalent metallic ions affected greatly the entrapment of glucoamylase in alginate fibers, the order of which followed roughly the ionotropic series of Thiele. Entrapment of glucoamylase in bicomponent systems comprising alginate and other water‐soluble polymers was also investigated.
Species selection in a reactor–settler system
Authors: Sheintuch Moshe
Published: December 2004

The competition between flocculating and nonflocculating microorganisms was investigated in a continuous reactor‐settler system (e.g. activated sludge). Co existence states were found to be possible, over a certain domain of operating conditions, even with simple monotonic kinetics and simple competition. Multiple solutions exist when coexistence states are unstable. Coexistence solutions are stable when the flocculating bacteria grow faster at feed conditions as in the activated sludge problem. The analysis applies to one or several mixed or plug flow reactors. Other effects, such as enrichment of the recycle stream by the flocculating microorganism or substrate adsorption and storage, may change the structure of solution.
Kinetic study and mathematical modeling of methanogenesis of acetate using pure cultures of methanogens
Authors: Yang S. T. , Okos M. R.
Published: December 2004

Kinetics of methanogenesis from acetate was studied using pure cultures of Methanosarcina barkeri and Methanosarcina mazei. Methane formation was found to be associated with cell growth. Nearly equimolar methane was produced from acetate during the methanogenic growth, and about 1.94 g of cells were formed from each mole of acetate consumed. Cell growth can be estimated from methane production. Significant substrate inhibition was found when acetate concentration was higher than 0.12 M. Among the three methanogenic strains studied, M. mazei strain S6 had the highest specific growth rate at all acetate concentrations studied and was least sensitive to environmental factors investigated (e.g., acetate concentration). The maximum specific growth rate found for strain S6 was 0.022 hr−1 at acetic acid concentration around 7 g/L. The other two strains studied were M. barkeri strain 227 and strain MS. Growth of M. barkeri was completely inhibited at sodium acetate concentrations higher than 0.24 M. The maximum specific growth rate found for strains 227 and MS was 0.019 and 0.021 h−1 at acetic acid concentrations of 3.6 and 6.8 g/L, respectively. A kinetic model with substrate inhibition was developed and can be used to simulate the methane formation from M. mazei strain S6 grown on acetate at 35°C, pH 7.
Substrate protection of immobilized glucose isomerase
Authors: Chen Kuo‐Cheng , Wu Juan‐Yih
Published: December 2004

Using commercial immobilized glucose isomerase (SWETASE®, Nagase Co.), the effect of substrate protection on enzyme deactivation has been studied in a batch manner. The data analysis was carried out based on Briggs‐Haldane kinetics in which enzyme deactivation accompanying the protection of substrates was also considered. The protection factor was proposed to elucidate the dependence of the degree of substrate protection. The existence of the protection of glucose isomerase by the substrates has been verified experimentally. Also, the enzyme‐substrate complex deactivates with a decay constant which is one‐half that of the free enzyme. Theoretical analysis of enzyme deactivation with substrate protection offers an effective understanding which is essential for enzyme replacement and process optimization.
A dynamic simulation of a two‐phase anaerobic digestion system for solid wastes
Authors: Mata‐Alvarez Joan
Published: December 2004

In this article, a two‐phase system for the digestion of wastes with a high solid content is simulated. The solids are charged to the hydrolyzer and then leachate recirculation is activated until biodegradation is nearly complete. Several parameters are tested, namely moisture, leachate recirculation flow rate, and hydrolyzer‐methanizer volume ratio. The results show that recirculation rate is an important parameter subject to optimization, with optimal values corresponding to hydrolyzer hydraulic retention times below 1 day. The quantity of recirculating water must be the highest possible. As a consequence, the organic load to the methanizer is reduced, making thus possible the use of a smaller methanizer volume.
Harvesting of Scenedesmus obliquus in wastewaters: Auto‐ or bioflocculation?
Authors: Lavoie Alain , de la Noüe J.
Published: December 2004

Autoflocculation and bioflocculation are considered to be the most promising means for the economical harvesting of microalgae. We have therefore studied these phenomena with cultures of Scenedesmus obliquus produced during biological tertiary wastewater treatment. The quantity of extracellular polymers produced during ageing of the cultures proved insufficient to initiate bio‐flocculation while the concentration of Ca2+ and PO43− of the treated effluent were too low to induce autoflocculation. It has been shown, however, that the algae sediment more readily upon ageing, possibly as a result of increased ceil density. The use of density gradients made with Percoll (a colloidal solution of silica particles) allowed measurement of the true cell density and showed that this increases when cultures enter the declining growth phase. The quality of the biomass thus harvested is, however, considerably impaired, protein content decreasing from 62.7% (dry wt) during the exponential growth phase (day 5) to 14% at the end of cultures (day 21).
Operating parameters' effects on the outcome of pure and simple competition between two populations in configurations of two interconnected chemostats
Authors: Kung Cheng‐Ming , Baltzis B. C.
Published: December 2004

It is known from the literature that two microbial populations competing purely and simply for a common substrate in a spatially inhomogeneous environment may under certain conditions coexist in a steady state. This paper studies pure and simple competition between two microbial species in three alternate configurations of two interconnected ideal chemostats and focuses on the effects of the operating parameters‐dilution rate, substrate concentration in the feed to the vessels, recycle ratio, and volume ratio of the two vessels, splitting ratio of the external feed to the chemostats‐on the coexistence of the two competitors. It is shown that the coexistence steady state is practically feasible in the sense that it occurs in a finite domain of the operating parameters space. Theoretical and numerical results are presented, some of them in the form of operating diagrams projected on the two‐dimensional subspace. A comparison of the three possible configurations is offered.
Enzymatic function of alginate immobilized rat hepatocytes
Authors: Tompkins Ronald G. , Carter Edward A. , Carlson James D. , Yarmush Martin L.
Published: December 2004

The use of immobilized hepatocytes represents a promising approach for the problem of detoxification in acute hepatic failure. Hepatocyte viability and detoxification function of a number of complex enzyme systems were examined before and after immobilization in alginate droplets. Detoxification function was assessed quantitatively by measuring the kinetics of several specific detoxification systems: the cytochrome P450 system, the urea cycle, and two conjugation systems. Reaction rates for all enzyme systems were similar in immobilized and nonimmobilized cells, and were in good agreement with previously published literature values. These results indicate that transport limitations do not occur in these gels and that the intrinsic reaction rate is the limiting step. Feasibility of detoxification replacement by immobilized cells is discussed using measured reaction rates.
Thermochemical pretreatment of lignocellulose to enhance methane fermentation: II. Evaluation and application of pretreatment model
Authors: Baugh Kent D. , Levy James A. , McCarty Perry L.
Published: December 2004

A model was developed and evaluated as a tool for predicting the formation of soluble products from staged thermochemical treatment of lignocellulosic materials under acidic conditions typical of autohydrolysis. The model was used to predict the general trend of hemi‐cellulose and cellulose hydrolysis between pH 2 and 4 and temperatures of 170–230°C, and results were compared with experimental data. When the model was evaluated for this range of temperatures and pH values, results indicated: (1) a relatively low temperature (175°C) during the first stage allows hydrolysis of the hemi‐cellulose polysaccharides without significant mono‐saccharide decomposition, (2) subsequent stages at higher temperatures (equal or greater than 200°C) are needed for significant cellulose hydrolysis, but glucose decomposition will also occur, and, (3) a pH in the range of 2–2.5 will enhance polysaccharide hydrolysis while limiting monosaccharide decomposition. The model's predictions, indicating that the formation of biodegradable products could be optimized using Pretreatments at pH 2–2.5 for the pH range evaluated, were confirmed in experiments with white fir as a representative lig nocellulose.
Photobioreactor design: Mixing, carbon utilization, and oxygen accumulation
Authors: Weissman Joseph C. , Goebel Raymond P. , Benemann John R.
Published: December 2004

Photobioreactor design and operation are discussed in terms of mixing, carbon utilization, and the accumulation of photosynthetically produced oxygen. The open raceway pond is the primary type of reactor considered; however small diameter (1–5 cm) horizontal glass tubular reactors are compared to ponds in several respects. These are representative of the diversity in photobioreactor design: low capital cost, open systems and high capital cost, closed systems. Two 100‐m2 raceways were operated to provide input data and to validate analytical results. With a planktonic Chlorella sp., no significant difference in productivity was noted between one pond mixed at 30 cm/s and another mixed from 1 to 30 cm/s. Thus, power consumption or CO2 outgassing limits maximal mixing velocities. Mixing power inputs measured in 100‐m2 ponds agreed fairly well with those calculated by the use of Manning's equation. A typically configured tubular reactor flowing full (1 cm diameter, 30 cm/s) consumes 10 times as much energy as a typical pond (20 cm deep flowing at 20 cm/s). Tubular reactors that flow only partially full would be limited by large hydraulic head losses to very short sections (as little as 2 m length at 30 cm/s flow) or very low flow velocities. Open ponds have greater CO2 storage capacity than tubular reactors because of their greater culture volume per square meter (100–300 L/m2 vs. 8–40 L/m2 for 1–5‐cm tubes). However, after recarbonation, open ponds tend to desorb CO2 to the atmosphere. Thus ponds must be operated at higher pH and lower alkalinity than would be possible with tubular reactors if cost of carbon is a constraint. The mass transfer coefficient, KL, for CO2 release through the surface of a 100‐m2 pond was determined to be 0.10 m/h. Oxygen buildup would be a serious problem with any enclosed reactor, especially small‐diameter tubes. At maximal rates of photosynthesis, a 1‐cm tubular reactor would accumulate 8–10 mg O2/L/min. This may result in concentrations of oxygen reaching 100 mg/L, even with very frequent gas exchange. In an open pond, dissolved oxygen rises much more slowly as a consequence of the much greater volume per unit surface area and the outgassing of oxygen to the atmosphere. The maximum concentration of dissolved oxygen is typically 25–40 mg/L. The major advantage of enclosed reactors lies in the potential for aseptic operation, a product value which justifies the expense. For most products of algal mass cultivation, open ponds are the only feasible photobioreactor design capable of meeting the economic and operating requirements of such systems, provided desirable species can be maintained.
Use of surface‐immobilized Trichoderma in batch and fed‐batch fermentations
Authors: Duff Sheldon J. B.
Published: December 2004

Needle‐punch polyester was shown to be an effective support material for the immobilization of Trichoderma reesei Rut C30. When used as a resident inoculum for a batch process, the immobilized Trichoderma was very stable and resulted in a reduced rate of biomass generation in the bulk liquid phase as compared to cultures inoculated with free mycelium. Fed‐batch fermentations with the immobilized Trichoderma produced ca. 80% of the activity of those using free cells; however, the activity was more stable and the crude enzyme broth produced had a greatly reduced biomass concentration.
Production of optically active 2,3‐butanediol by Bacillus polymyxa
Authors: De Mas Carles , Jansen Norman B. , Tsao George T.
Published: December 2004

Bacillus polymyxa produces (R, R)‐2,3‐butanediol from a variety of carbohydrates. Other metabolites are also produced including acetoin, acetate, lactate, and ethanol. The excretion of each metabolite was found to depend on the relative availability of oxygen to the culture. When the relative oxygen uptake rate was high, enhanced yields of acetate and acetoin were noted. At an intermediate oxygen availability, the butanediol yield was maximal. When the availability of oxygen was more restricted, higher yields of lactate and ethanol occurred. The cells appeared to regulate themselves such that energy generation is optimal subject to the constraint that the cells do not produce more reducing equivalents than can be oxidized by the electron transport system. The dependence of each product yield on the relative oxygen availability was determined, and this knowledge was used to carry out a fed‐batch fermentation that attained a final butanediol concentration of over 40 g/L in 50 h.
The relationship between fiber‐porosity and cellulose digestibility in steam‐exploded Pinus radiata
Authors: Wong Ken K. Y. , Deverell Kay F. , Mackie Keith L. , Clark Tom A. , Donaldson Lloyd A.
Published: December 2004

Steam explosion after sulphur dioxide impregnation of wood chips is an effective method for improving the enzymatic digestibility of cellulose in the softwood Pinus radiata. Digestibility of pretreated fiber was progressively increased by altering the conditions of steam explosion. With increasing digestibility, there was an observed increase in fiber porosity as measured by the solute exclusion technique. Accessible pore volume and accessible surface area to a 5‐nm dextran probe positively correlated with both 2‐ and 24‐h digestion yields from pretreated fiber. The increase in accessibility was probably the result of hemicellulose extraction and lignin redistribution. A subsequent loss in accessibility, brought about by structural collapse or further lignin redistribution, resulted in a corresponding loss in digestibility. It appears that steam explosion increases cellulose digestibility in P. radiata by increasing fiber porosity.
Effect of cycling on the stability of plasmid‐bearing microorganisms in continuous culture
Authors: Stephens M. L. , Lyberatos G.
Published: December 2004

The implication of the possible existence of differences in the times required for plasmid‐bearing and non‐plasmid‐bearing microorganisms to adjust their metabolic activities to step changes in their environment is examined. This adaptability difference suggests the possibility of maintaining an engineered strain in continuous culture by transient operation. It is shown for the case where adaptability is neglected that no cycling strategy will prevent the washout of the engineered strain, but the addition to the model of a time delay in substrate utilization can result in coexistence upon cycling. Numerical simulations of cycling in feed substrate concentration are carried out to illustrate the concept Operating diagrams are also constructed to indicate the conditions under which washout of the plasmid bearing strain can be prevented.
The anion‐exchange substrate shuttle process: A new approach to two‐stage biomethanation of organic and toxic wastes
Authors: Thiele Jurgen H. , Zeikus J. Gregory
Published: December 2004

A novel biomethanation process configuration is described which uses improved biocatalysts to enhance the productivity and stability of waste biomethanation systems. The design facilitates the maintenance of acetogenic and methanogenic bacteria under optimum substrate concentrations far above their Ks values in a two‐stage biomethanation system with closed loop reactors. Volatile fatty acid anions (VFA anions) are provided as substrates for the methanogenic stage by using an anion exchange unit coupled to the acidogenic stage. The slow growing and sensitive acetogenic and methanogenic bacteria are protected from oxygen, cationic pollutants, toxins, and microbial contamination by use of the substrate shuttle process. Due to the closed loop process configuration, washout of the ecoengineered biocatalysts is excluded. The modular system configuration allows industrial mass production of the system components. The new biomethanation process enhances both the BTU content of the gas and the methane production over state‐of‐the‐art anaerobic digestor bioreactor concepts.
Gluconic acid production by an mobilized glucose oxidase reactor with electrochemical regeneration of an artificial electron acceptor
Authors: Bourdillon Christian , Lortie Robert , Laval Jean Marc
Published: December 2004

A reactor, using the enzymatic electrocatalysis scheme, was developed on a laboratory preparative scale for the catalytic oxidation of glucose into gluconic acid. Glucose oxidase was directly immobilized on the surface of a carbon felt electrode and a solution of glucose and benzo‐quinone passed through the electrode in order to regenerate the electron acceptor. The reactor was able to produce continuously 1.5 g gluconate/h with a catalytic current of 0.4 A. This gave a high productivity ca. 100 g/h/L reactor. A one‐dimensional model was developed which demonstrated the efficiency of coupling between enzymatic and electrochemical reactions due to the proximity of the two reaction sites. For example the catalytic current was practically independent of mass transfer parameters. The operational stability of immobilized glucose oxidase was increased 50 times at least when electroregenerated benzoquinone was used as oxidant instead of oxygen.
Biodegradation by immobilized bacteria in an airlift‐loop reactor—influence of biofilm diffusion limitation
Authors: Wagner K. , Hempel D. C.
Published: December 2004

Naphthalene‐2‐sulfonate was degraded by submerse growing Pseudomonads in a chemostat culture. The kinetic parameters for the Monod equation, including Pirts maintenance energy, were calculated from these experiments regarding naphthalene‐2‐sulfonate as substrate and oxygene as cosubstrate. By immobilizing the bacteria on sand particles, the degradation of naphthalene‐2‐sulfonate was carried out in a specialy designed three‐phase airlift‐loop reactor in a completely fluidized state. From these experiments, the influence of biofilm diffusion limitation on reaction kinetics and criteria for stable biofilm formation on sand particles were obtained.
Experimental simulation of oxygen profiles and their influence on baker's yeast production: I. One‐fermentor system
Authors: Sweere A. P. J. , Mesters J. R. , Janse L. , Luyben K. Ch. A. M. , Kossen N. W. F.
Published: December 2004

In production‐scale bioreactors microorganisms are exposed to a continually changing environment. This may cause loss of viability, reduction of the yield of biomass or desired metabolites, and an increase in the formation of by‐products. In fed‐batch production of baker's yeast, profiles may occur in substrate and oxygen concentrations and in pH. This article deals with the influence of a periodically changing oxygen concentration on the growth of baker's yeast in a continuous culture. Also, influences on the production of ethanol, glycerol, acetic acid, and on the composition of the cells were investigated. It was found that relatively fast fluctuations between oxygen‐unlimited and oxygen‐limited conditions with a frequency of 1 or 2 min had a distinct influence on the biomass and metabolite production. However, RNA, protein, and carbohydrate contents measured in cells exposed to fluctuations differed little from those in cells from an oxygen‐unlimited or an oxygen‐limited culture. The respiration and fermentation capacities of cells exposed to fluctuations can be larger than the capacities of cells grown under oxygen‐unlimited conditions.
Improvements in ethanol tolerance of Kluyveromyces fragilis in jerusalem artichoke juice
Authors: Rosa M. Fernanda , Correia Isabel Sá , Novais Júlio M.
Published: December 2004

Alcoholic fermentation of Jerusalem artichoke juice, a natural complex medium, allowed the production of 13% (v/v) ethanol utilizing an inulin‐fermenting strain of Kluyveromyces fragilis, strongly sensitive to ethanol. However, the fermentation of a simple medium with a similar concentration of fermentable sugars (235 g/L) as saccharose stopped prematurely when only 7% (v/v) ethanol had been produced. Differences in the two fermentation profiles were attributed to the significantly lower ethanol tolerance of K. fragilis IGC 2671 in the simple medium with 2% saccharose as compared with diluted J.a. juice with a similar sugar concentration, in fact, (1) in diluted J. a. juice, growth was possible up to 8% (v/v) added ethanol compared with 6% (v/v) in simple medium and (2) ethanol‐induced inhibition of the specific growth and fermentation rate as well as ethanol‐induced stimulation of the specific death rate were much more drastic in simple medium. Present results show that (1) the complex composition of the medium used for alcoholic fermentation plays a marked role in the ability of the yeast to tolerate and produce ethanol; (2) J. a. juice proved a very appropriate medium for a productive alcoholic fermentation, namely, in processes based on strains with a low ethanol resistance; and (3) to characterize and compare the ethanol tolerance of fermenting yeasts, the standardization of the medium composition must be taken in consideration.