bluuebunny/crossref_metadata_2025 huggingface dataset:
Butanediol production by Aerobacter aerogenes NRRL B199: Effects of initial substrate concentration and aeration agitation
Authors: Sablayrolles J. M. , Goma G.
Published: December 2004

Butanediol production by Aerobacter aerogenes NRRL B199 grown on glucose requires an optimal rate of aeration for the obtention of butanediol 2, 3. In the absence of air, Aerobacter aerogenes NRRL B199 growth and production are weak. Agitation‐aeration is necessary for producing the biomass, but an excess of oxygen proves to be toxic with regard to metabolite production. Oxygen is a limiting substrate with regard to growth and an inhibitor with regard to the specific metabolite productivity. This observation is discussed from a kinetic stand point and in relation to the search for the optimum oxygen transfer coefficient (KLa), which is found to be in the range of 50–100h−1. It has also been observed that KLa increases during the fermentation cycle. The initial substrate concentration effects the yield production of biomass and butanediol production. Low yields of butanediol are obtained at low initial sugar concentrations, but good yields of butanediol are obtained (0.45 g/g) at high concentrations of glucose (195 g/L). Carbon substrates and butanediol are inhibitors of cell growth while butanediol is not quite an inhibitor of the specific rate of butanediol production for the range of butanediol of 0–100 g/L.
Computer model for glucose‐limited growth of a single cell of Escherichia coli B/r‐A
Authors: Domach M. M. , Leung S. K. , Cahn R. E. , Cocks G. G. , Shuler M. L.
Published: December 2004

A computer model is described which is capable of predicting changes in cell composition, cell size, cell shape, and the timing of chromosome synthesis in response to changes in external glucose limitation. The model is constructed primarily from information on unrestricted growth in glucose minimal medium. The ability of the model to make reasonable quantitative predictions under glucose‐limitation is a test of the plausibility of the basic biochemical mechanisms included in the model. Such a model should be of use in differentiating among competing hypotheses for biological mechanisms and in suggesting as yet unobserved phenomena. The last two points are illustrated with the testing of a mechanism for the control of the initiation of DNA synthesis and predictions on cellwidth variations during the division cycle.
Increased digestibility of bagasses by pretreatment with alkalis and steam explosion
Authors: Playne M. J.
Published: December 2004

Alkali treatment and steam explosion of bagasse were investigated in order to develop economical and effective methods of increasing the digestibility of bagasse. The treated bagasse was to be used as a substrate for the production of volatile fatty acids by anaerobic acidogenic bacteria. The alkalis examined were NaOH, NH3 (aqueous), NaOH + NH3, Ca(OH)2, and Ca(OH)2 + Na2CO3, at ambient temperature and in combination with steam explosion at 200°C, 6.9 MPa, and 5 min cooking times. Digestibilities of up to 733 g organic matter (OM)/kg bagasse dry matter (DM) were obtained for bagasse treated with NaOH and Ca(OH)2 + Na2CO3; less than 430 g OM was obtained for bagasse treated with aqueous NH3; and up to 724 g OM was obtained for bagasse treated with Ca(OH)2. This digestibility was only achieved by using high concentrations of Ca(OH)2, i.e., 180–300 g/kg bagasse. Steam explosion increased the digestibility of bagasse up to 740 g OM in the presence of alkali but only to 610 g OM in the absence of alkali. The digestibility of bagasse without pretreatment was 190 g OM/kg bagasse DM. More than one‐half the hemicellulose present was solubilized by pretreatment. The composition of the liquid fraction of steam‐exploded material was examined and contained mainly xylose monomers and oligomers (112 g/kg original bagasse DM) and acetic acid (33 g/kg original DM). The relative costs of the alkalis used were obtained for the United States, Australia, and Europe. Lime [Ca(OH)2] was the least expensive alkali per unit of additional digestible OM obtained. Ammonia was the most expensive alkali to use, except in the United States where the difference in its cost relative to other alkalis was smaller. However, ammonia provides organic nitrogen for microbial growth, and could be recycled. With acidogenic fermentations, alkali is able to double as a neutralizing agent during fermentation. Thus, concentrations of alkali equal to that required for neutralization may be used in pretreatment. Concentrations of Ca(OH)2 as high as 300 g/kg bagasse were needed for neutralization and should, therefore, be considered for pretreatment. Steam explosion of bagasse resulted in digestible, sterilized substrates of small particle size with readily separable liquid and pulp streams.
Thermodynamics of water and ethanol adsorption on four starches as model biomass separation systems
Authors: Rebar V. , Fischbach E. R. , Apostolopoulos D. , Kokini J. L.
Published: December 2004

Adsorption of water and ethanol on four starches has been studied in the temperature range of 50–90°C. The results show that adsorption of water on starch‐based materials is enhanced when the amount of amylopectin is highest. Adsorption of ethanol is not significantly affected by the kind of starch used. Heats of adsorption calculated from retention data are in the range from −9.3 to −13.7 kcal/g mol for water and −5.6 to −6.76 kcal/g mol for ethanol. Calculated free energies of adsorption suggest that adsorption is most spontaneous at lower temperatures as expected.
Continuous enzymatic cooking and liquefaction of starch using the technique of direct resistive heating
Authors: Varella V. L. , Concone B. R. V. , Senise J. T. , Doin P. A.
Published: December 2004

Continuous cooker prototypes of very simple design, using electricity as a primary energy source, were developed for the process of cooking and liquefaction of starch suspensions. Previous work on equipment using microwave dielectric heating has already been reported. Results of energy consumption as low as 330 kcal/kg based on starch content were achieved. Considering these results and looking for new solutions or engineering concepts, the authors have been investigating the possibility of using electric energy at 60 Hz for direct resistive heating, in which the starch suspension is the proper “resistor.”

The most important results of energetic yield obtained until now, working in a continuous process of cooking–liquefaction, are not larger than 235 kcal (272 Wh)/kg based on starch content. These results were obtained using a commercial grade α‐amylase from B. subtillis, working with temperatures ranging from 70 to 75°C, and with residence times in the reactor not greater than 1.5 min. The experiments of saccharification and fermentation accomplished as a test for the efficiency of this heating technique gave good results (as with a conventional technique) and thus enabled us to proceed with the studies.
Characterization of algae using regularities
Authors: Lee H. Y. , Erickson L. E.
Published: December 2004

The weight fraction carbon and reductance degree of algae are reviewed for literature data. Average values are compared with values for yeast and bacteria. The results show that the standard deviation and coefficient of variation are small as long as the algae are grown under adequate nutritional conditions. For nitrogen‐deficient growth conditions, the storage of lipids has been observed; this results in values of weight fraction carbon and reductance degree which are larger than the average values.
Hydrolysis of milk lactose by immobilized β‐galactosidase–hen egg white powder
Authors: Kaul Rajni , D'Souza S. F. , Nadkarni G. B.
Published: December 2004

Immobilized β‐galactosidase was obtained by crosslinking the enzyme with hen egg white using 2% glutaraldehyde. The gel obtained could be lyophilized to give a dry enzyme powder. The pH optimum of both the soluble and immobilized enzyme was found to be 6.8. The immobilized enzyme showed a higher Km for the substrates. The extent of enzyme inhibition by galactose was reduced upon immobilization. The stability towards inactivation by heat, urea, gamma irradiation, and protease treatment were enhanced. The bound enzyme as tested in a batch reactor could be used repeatedly for the hydrolysis of milk lactose. The possible application of this system for small‐scale domestic use has been suggested.
Enzymatic hydrolysis of inulin to fructose by glutaraldehyde fixed yeast cells
Authors: Workman Wesley E. , Day Donal F.
Published: December 2004

Inulin, a polyfruction, is found as the reserve carbohydrate in the roots and tubers of various plants (i.e. Jerusalem artichoke, chicory, and dahlia tubers). The β‐fructofuranosidase (inulase) from the yeast Kluyveromyces fragilis is of interest because of its industrial potential in fructose syrup and alcohol production from inulin containing plants. We have found that the inulase of K. fragilis can be immobilized in the yeast cells by glutaraldehyde treatment. These cells are resistant to physical and enzymatic destruction. Although the exact nature of the immobilization is not fully understood, the kinetic parameters of the immobilized enzyme are similar to those of the soluble enzyme. No reduction of enzyme activity was observed after glutaraldehyde treatment and glutaraldehyde concentration did not affect enzyme activity. A 96% hydrolysis of dahlia inulin was achieved in 10.5 h with a 9.5% (w/v) fixed enzyme suspension. A Jerusalem artichoke extract containing 16.8%polyfructan was completely hydrolyzed in 3.5 h with a 0.24% (w/v)fixed enzyme suspension. This is a time frame feasible for industrial consideration.
Control strategies of continuous bioprocesses based on biological activities
Authors: Meyer C. , Beyeler W.
Published: December 2004

Based on the material balance principle applied to microbial reactions in continuous bioprocesses, the concept of reaction rate control has been developed theoretically. This concept provides a more direct way of controlling biological activities than the control of physical or chemical parameters in practice today. From an analysis of dynamic and steady‐state experiments, two control systems for carbon dioxide production rate control during the continuous culture of baker's yeast have been designed and evaluated experimentally. In these control methods, intracellular NADH concentration is used as an immediate indication of the onset of glucose repression. A more sophisticated master controller based on the respiratory quotient can be combined with these control methods. The resulting control system provides a means to indirectly optimize biomass production while preventing ethanol formation in the continuous culture of baker's yeast.
Stabilization of soluble and immobilized horse liver alcohol dehydrogenase by adenosine 5′‐monophosphate
Authors: Görisch Helmut , Schneider Manfred
Published: December 2004

Horse liver alcohol dehydrogenase, which catalyzes oxidoreductions for a broad spectrum of substrates of organic chemical interest, was immobilized on CNBr‐activated Sepharose and on decylamine‐substituted agarose. The specific activities of the immobilized enzyme preparations were compared with the free enzyme, and the apparent Km values of the preparations were determined for a selection of substrates. At pH 9 and 60°C, soluble liver alcohol dehydrogenase was rapidly inactivated, while the enzyme immobilized on CNBr‐activated Sepharose was more stable. Adenosine monophosphate (AMP), adenosine diphosphate, and adenosine diphosphoribose protected the free and immobilized alcohol dehydrogenase against heat inactivation. On storage under a variety of conditions, AMP effectively stabilized free horse liver alcohol dehydrogenase and the immobilized preparations.
Effects of temperature on plasmid stability and penicillinase productivity in a transformant of Bacillus stearothermophilus
Authors: Aiba Shuichi , Koizumi Jun‐ichi
Published: December 2004

After transforming host cells of Bacillus stearothermophilus CU21 with a recombinant plasmid pLP11 that harbored constitutive penicillinase genes of B. licheniformis CO1, both the stability of the plasmid and specific rate of penicillinase production were studied. The temperature at which the plasmid could be kept in a stable fashion in the transformant of B. stearothermophilus CU21 (pLP11) ranged nearly from 44 to 50°C, irrespective of batch and continuous cultures. Continuous and steady‐state cultures of the transformant could only be realized within this narrower temperature range. Indeed, the approximate temperature ranges of growth for the host and transformant were from 40 to 70°C and from 40 to 63°C, respectively. Clearly, the upper limit for the growth temperature of host cells decreased when they were transformed. Kinetic patterns of penicillinase production in continuous culture of the transformant (with plasmid) from 44 to 50°C differed remarkably from that of B. licheniformis CO1 (without plasmid) at 37°C.
Effect of crystallinity and degree of polymerization of cellulose on enzymatic saccharification
Authors: Puri Vinod P.
Published: December 2004

Lignocellulose materials were pretreated by methods known to improve enzymatic saccharification, and the percentage crystallinity (x‐ray diffraction) and degree of polymerization were measured. It was observed that although the percentage crystallinity of cellulose was not altered by alkaline explosion (AE), carbon dioxide explosion (CE), ozone, and sodium chlorite treatment, very great increases were obtained in the extent of enzymatic saccharification. All the pretreatments studied except sodium chlorite caused significant reduction in degree of polymerization. It appears likely that the rate and extent of saccharification is governed by particle size, surface area, and degree of polymerization, since crystallinity effects alone do not explain the observed trends in the hydrolysis data.
Physical and chemical conditions for microbial oil degradation
Authors: Berwick Paul G.
Published: December 2004

Oil residues arising from the Christos–Bitas spillage were found to contain 28% of oil extractable by carbon tetrachloride; the remainder comprised water and undefined solids. When incubated in 8‐L rectangular tanks with a mixed population of mainly bacteria to which diammonium hydrogen phosphate was added, ca. 97% of the Christos‐Bitas oil fraction was degraded. When the same substrate was degraded by only three isolated Pseudomonas strains in 1‐L cylindrical tanks, degradation was only ca. 56%. Raising the temperature from 20 to 50°C brought about a visible loss in cell viability with only ca. 38% of the substrate degraded. Oil degradation proceeded in direct proportion to increases in cell attachment to the dispersed oil. The aliphatic fraction of Kuwait crude oil up to nC25 measured by gas liquid chromatography (GLC) was oxidized within 48 h. Using this substrate the three pseudomonads together brought about a more complete degradation (87%) than a single Bacillus isolate. The Bacillusstrain was capable of deggrading between 50 and 65% of the crude, depending on whether diammonium hydrogen phosphate supplemented a peptone‐based medium. The preferential biodgradability of fractions was the following aliphatics > aromatics > asphalts, as has been widely reported.
Bacterial removal of mercury from sewage
Authors: Hansen Conly L. , Zwolinski Gary , Martin Debra , Williams Jeffrey W.
Published: December 2004

Mercury‐resistant bacteria, which are able to reduce mercuric ion (Hg2+) to metallic mercury (Hg0), were examined for their ability to remove mercury from waste‐water aerobically. Growth studies in artificial medium indicated that mercury increases the lag phase, but does not effect the growth rate of these bacteria. Further studies demonstrated that growth was minimal during a phase of rapid mercury removal, after which growth resumed. Small but significant amounts of carbohydrates are required for the mercuric ion reduction. Prolonged periods of bacterial growth under nonsterile conditions was accomplished without the loss of the mercuric reducing ability of the culture. A continuous culture of the resistant organism was maintained on raw sewage for two weeks, during which time relatively high concentrations of mercury (70 mg/L) were removed from the sewage at a rate of 2.5 mg/L h and at efficiencies exceeding 98%.
Genetically structured models forlac promoter–operator function in the Escherichia coli chromosome and in multicopy plasmids: Lac operator function
Authors: Lee Sun Bok , Bailey James E.
Published: December 2004

A mathematical model based on known molecular interactions has been formulated to describe quantitatively regulation of expression of the lactose (lac) operon in the Escherichia coli chromosome and in multicopy plasmids. This model is genetically structured such that a nucleotide sequence change affecting transcription initiation at the lac promoter–operator influences one or very few directly corresponding model parameters. The model simulates chromosomal lac operon function in good agreement with previous experimental measurements for many lacl and lacO mutant systems as well as for diploid cells which carry F'lac episomes. Simulation results clearly show the loss of cloned lac operator regulation as the plasmid copy number increases, in agreement with experimental trends. The importance of this class of models in designing DNAs, organisms, and reactors for precise regulation of cloned gene expression is discussed.
Studies on immobilized fungal spores for microbial transformation of steroids: 11 α‐Hydroxylation of progesterone with immobilized spores of Aspergillus ochraceus G8 on polyacrylamide gel and other matrices
Authors: Bihari Vinod , Goswami P. P. , Rizvi S. H. M. , Khan A. W. , Basu S. K. , Vora V. C.
Published: December 2004

Hydroxylation in the 11 α‐position in the progesterone molecule employing immobilized spores of Aspergillus ochraceus strain No. G8 (CDRI catalogue No.) was achieved. For immobilization the activity of the spores was evaluated on a variety of matrices such as alginate beads, epoxy resin beads, polyacrylamide gel, and collagen. Spores entrapped in polyacrylamide gel were found to be the most active. Studies of various parameters, e.g. monomer content, cell loading capacity, optimum pH, temperature, and substrate concentration, were carried out on polyacrylamide gel. In polyacrylamide, the entrapped spores normal decay pattern, as indicated by loss of activity, was observed after four uses. At the end of 15 cycles, the residual activity was found to be 18% of the original. It was possible to regenerate the activity by incubating the preparation in a nutrient medium. The regenerated spores showed increasing rate of loss of activity upon recycling.
Optimization of fermentation conditions for alcohol production
Authors: Bowman Llewellyn , Geiger Edwin
Published: December 2004

The quantitative effects of carbohydrate levels, degree of initial saccharification, glucoamylase dosage, temperature, and fermentation time were investigated using a Box–Wilson central composite design protocol. WithSaccharomyces cerevisiaeATCC 4126, it was found that the use of a partially saccharified starch substrate markedly increased yields and attainable alcohol levels. Balancing the degree of initial saccharification with the level of glucoamylase used to complete hydrolysis was found necessary to obtain optimum yields. The temperature optimum was found to be 36°C. The regression equations obtained were used to model the fermentation in order to determine optimum fermentation conditions.
A comparative study of the enzymatic hydrolysis of acid‐pretreated white pine and mixed hardwood
Authors: Grethlein H. E. , Allen D. C. , Converse A. O.
Published: December 2004

Removal of hemicellulose by acid pretreatment in a flow reactor followed by enzymatic hydrolysis of the neutralized slurry has resulted in glucose yields as high as 95% for mixed hardwood. For white pine, however, the maximum glucose yield is 65%. Although pine has a higher extractives content, removal of the extractives prior to enzymatic hydrolysis does not increases the glucose yield. Pore size measurements reveal that the increase in pore volume, in the size range of the cellulase molecule, following pretreatment for pine is only about one‐half the value obtained with mixed hardwood. This suggests that pore volume is an important determinant of substrate–enzyme reactivity.
Fed‐batch cultivation of Cellulomonas on sugarcane bagasse pith
Authors: Rodríguez Hilda , Enríquez Antonio
Published: December 2004

A high biomass concentration (19.9 g/L) was obtained with the fed‐batch cultivation of Cellulomonas on pretreated sugarcane bagasse pith. Similar results in biomass concentration, yield, and substrated consumption were obtained with the discontinuous feed of bagasses as with discontinuous feed supplemented with a partial continuous addition of salts. Two or more growth phases were detected, probably caused by the differential utilization of bagasse components. An acceptably low content of bagasse components remained in the biomass after separation.
Optimization of microencapsulation parameters: Semipermeable microcapsules as a bioartificial pancreas
Authors: Goosen Mattheus F. A. , O'Shea Geraldine M. , Gharapetian Hrire M. , Chou Sheng , Sun Anthony M.
Published: December 2004

An improved membrane has been developed for the microencapsulation of islets of Langerhans which protects these cells from the immune system. These requirements were accomplished through the optimization of important microencapsulation parameters and through the improved biocompatibility of a new alginate‐poly‐l‐lysine (PLL)–alginate capsule membrane. Spherical and smooth microcapsules could be formed by utilizing a purer sodium alginate and by keeping the viscosity of the sodium alginate solution above 30 cps. The strength of the capsule membrane was enhanced by increasing the alginate–PLL reaction time as well as the PLL concentration. The permeability of the membrane [4 μm thick, 93% (w/w) water] was a function of the viscosity average molecular weight (Mv) of the PLL (Mv = 4000−4 × 105) used in the encapsulation procedure. Microcapsules prepared with PLL with Mv = 1.7 × 104 were the least permeable, being impermeable to normal serum immunoglobulin, albumin, and haemoglobin. The microencapsulation procedure, by protecting transplanted tissue from the components of the immune system, has great clinical potential as a new form of treatment for diseases such as diabetes and liver disease.
Nutrient‐limited continuous culture in the phauxostat
Authors: Rice Craig W. , Hempfling Walter P.
Published: December 2004

Stable steady‐state growth of Escherichia coli B limited by succinate, phosphate, or sulfate ion over the range of specific growth rates of 0.025–0.51 h−1 was achieved using pH‐controlled auxostasis in the phauxostat. The concentration of the growth‐limiting substrate in the growth vessel could be varied at will in the region of the Monod half‐maximal saturation constants by adjusting the concentration of that substrate in the reservior (at constant buffering capacity) or by varying the population density of the culture through changing the buffering capacity of the medium in the reservoir.
Effect of pretreatments and fermentation on pore size in cellulosic materials
Authors: Lin K. W. , Ladisch M. R. , Voloch M. , Patterson J. A. , Noller C. H.
Published: December 2004

Surface area has been proposed as a major factor determining the extent of enzymatic hydrolysis of cellulose. We used cornstalk residue (CR) and Solka Floc BW‐300 (SF) as substrates and NaOH (a cellulose swelling agent) and iron sodium tartrate (FeTNa, intercolates between cellulose microfibrils) as pretreatments to study the effect of surface area on extent of fermentation. Micropore sizes (8‐130 Å) were determined by a solute exclusion technique using glucose, cellobiose, and polyethylene glycols as molecular probes. The pore size distributions follow the logistic model function: I = a/[1+exp(b − cX)] where I is pore volume; X = log D; D is the molecular probe diameter; and a, b, and c are constants. The pore volumes of CR (1.9 mL/g) and SF (1.6 mL/g) are increased to 2.1 mL/g by pretreatment with NaOH. Pretreatment of SF with NaOH and cornstalk residue with FeTNa caused an upward shift in the pore size distribution. Fermentation of untreated CR by rumen microbes resulted in a 46% loss of dry matter while increasing the internal pore size and decreasing the pore volume to 0.9 mL/g. Fermentation of NaOH pretreated CR resulted in a 73% loss of dry matter with little change in pore size, total pore volume, or fiber composition. Fiber analysis indicated that selective utilization of hemicellulose over cellulose in both fermentations was small. The data show that: (1) removal of hemicellulose and lignin increases dry matter disappearance upon fermentation of the remaining material; (2) relative to the size of bacterial cellulases (40‐160 Å), the pretreatments have little effect on increasing accessibility of surface internal to the cellulose particles; and (3) the micropore changes caused by NaOH or FeTNa treatment do not explain the enchanced fermentation obtained for treated cornstalk residue. These observations infer that external or macropore surface properties may be a significant factor in determining the extent of utilization of the solid substrates by cellulolytic microorganisms.
Dynamics of a chemostat in which one microbial population feeds on another
Authors: Pavlou Stavros
Published: December 2004

Under certain simplifying hypotheses, a chemostat in which one microbial population feeds on another can be described by a system of three ordinary differential equations. A study is conducted to find which features of the equations are the most important to the dynamics of the system; it is found that the main influence comes from the from the particular form of the specific growth rate of the feeding population. Some conditions are derived that relate the form of the specific growth rate of the feeding population to the dynamic behaviour of the system.
Maltodextrin hydrolysis in a fluidized‐bed immobilized enzyme reactor
Authors: Vallat I. , Monsan P. , Riba J. P.
Published: December 2004

The present work deals with maltodextrin hydrolysis by glucoamylase immobilized onto corn stover in a fluidized bed reactor. An industrial enzyme preparation was covalently grafted onto corn stover, yielding an activity of up to 372 U/g and 1700 U/g for support particle sizes of 0.8 and 0.2 mm, respectively. A detailed kinetic study, using a differential reactor, allowed the characterization of the influence of mass transfer resistance on the reaction catalyzed by immobilized glucoamylase. A simple and general mathematical model was then developed to describe the experimental conversion data and found to be valid.
Effects of chemical modification on enzymatic activities and stabilities
Authors: Sadana Ajit , Henley James P.
Published: December 2004

The influence of chemical modification on the initial specific activity, residual activity, and deactivation kinetics of various enzymes is analyzed using a series mechanism. This straightforward multistate sequential model presented is consistent with the enzyme deactivation data obtained from different fields. The enzymes are placed in five different categories depending on the effect of chemical modification on initial specific activity and residual activity or stability. Wherever possible, structure–function relationships are described for the enzymes in the different categories. The categorization provides one avenue that leads to further physical insights into enzyme deactivation processes and into the enzyme structure itself.
Comparative study of the effect of ferrocyanide and EDTA on the production of ethyl alcohol from molasses by Saccharomyces cerevisiae
Authors: Oderinde Rotimi A. , Ngoka Lambert C. , Adesogan E. Kayode
Published: December 2004

The effects of potassium ferrocyanide and EDTA on ethyl alcohol production from molasses by Saccharomyces cerevisiae were investigated on simulated batch pilotplant‐scale conditions for alcoholic fermentation of molasses. Ethyl alcohol production was more sensitive to ferrocyanide than to EDTA. When ferrocyanide was introduced into the cultures at the time of inoculation, there was stimulation of ethyl alcohol production, with 261 ppm ferrocyanide producing the maximum effect, which was 3.0% more than in control cultures. When added during the propagation of the yeast, ferrocyanide depressed ethyl alcohol production by 4.0% maximum whereas EDTA stimulated ethyl alcohol production by 2.0%. Addition of ferrocyanide during the fermentation stage produced no significant effect on alcohol production, whereas over a wide range of EDTA concentration there was a steady increase in alcohol yield.
A kinetic model for anaerobic digestion of biological sludge
Authors: Pavlostathis Spyros G. , Gossett James M.
Published: December 2004

The principal objective of this study was the development and evaluation of a comprehensive kinetic model capable of predicting digester performance when fed biological sludge, preliminary conversion mechanisms such as cell death, lysis, and hydrolysis responsible for rendering viable biological sludge organisms to available substrate were studied in depth. The results of this study indicate that hydrolysis of the dead, particulate biomass—primarily consisting of protein—is the slowest step, and therefore kinetically controls the overall process of anaerobic digestion of biological sludge. A kinetic model was developed which could accurately describe digester performance and predict effluent quality.
An integral dynamic model for the UASB reactor
Authors: Bolle W. L. , van Breugel J. , van Eybergen G. C. , Kossen N. W. F. , van Gils W.
Published: December 2004

In this article a dynamic model of a continuous working UASB reactor is described. It results from the integration of the fluid flow pattern in the reactor, the kinetic behavior of the bacteria (where inhibition and limitation were taken into account), and the mass transport phenomena between different compartments and different phases. The mathematical equations underlying the model and describing the important mechanisms were programmed and prepared for computations and simulations by computer. The settler efficiency has to be over 99% to prevent the reactor from wash‐out. When the settler efficiency is over 99%, the total sludge content of the reactor increases steadily, so the reactor is hardly ever in a steady state. This implies dynamic modeling. The model is able to predict the various observable and nonobservable or difficult to observe state variables, e.g., the sludge bed height, the sludge blanket concentration, the short‐circuiting flows over bed and blanket, and the effluent COD concentration as a function of the hydrodynamic load, COD load, pH, and settler efficiency. The optimal pH value is between 6.0 and 8.0; fatty acid shock loadings are difficult to handle outside this optimal pH range.
Substrate conditions that influence the assays used for determining the β‐glucosidase activity of cellulolytic microorganisms
Authors: Breuil C. , Mayers P. , Saddler J. N.
Published: December 2004

Culture filtrates from Trichoderma harzianum E58, T. reesei CL 847 and Penicillium sp. C 462 were assayed for β‐glucosidase activity using a range of substrates and sugar analysis methods. Although sugar analyses by the dinitrosalicylic acid (DNS) and Nelson–Somogyi methods gave a similar profile, when increasing concentrations of salicin were assayed, considerably higher values were obtained with the DNS assay. The salicin concentration used for the assay greatly influenced the final β‐glucosidase values with higher values obtained for T. harzianum E58 and T. reesei CL 847 at substrate concentrations of 1 mg/mL while optimum values for Penicillium sp. C 462 were obtained at substrate concentrations greater than 3 mg/mL. Low concentrations of salicin and p‐nitro‐phenyl‐β‐D‐glucopyranoside (PNPG) gave the same response as cellobiose. Cellobiose should be used at concentrations greater than 3.74 mg/mL to avoid substrate limitation of the β‐glucosidase assay.
Regeneration of NAD+ cofactor by photosensitized electron transfer in an immobilized alcohol dehydrogenase system
Authors: Julliard M. , Le Petit J. , Ritz P.
Published: December 2004

The irradiation with visible light of a photosensitizer dye like methylene blue was used to regenerate by electron transfer the oxidized form of a pyridine nucleotide coenzyme (NAD+). The process has been studied on a common enzymatic reaction: ethanol oxidation by alcohol–NAD+ oxidoreductase immobilized on polyacrylamide gel or porous glass balls. In the experimental conditions used, the initial NAD+ recycling rates were 2.33 × 104 cycles/h (polyacrylamide) and 3 × 104 cycles/h (glass balls). A total number of 49.5 × 104 cycles was obtained for 13 runs of 2 h. The enzyme immobilization strongly increased its stability: after 28 days at 20°C, the residual activity was 25% of the initial value.
Production of the macrolide antibiotic tylosin in cyclic fed‐batch culture
Authors: Gray P. P. , Vu‐Trong K.
Published: December 2004

Tylosin‐producing Streptomyces fradiae was cultured on a synthetic medium with a high glutamate–glucose ratio. Tylosin batch fermentations with this medium were characterized by a high initial specific production rate of tylosin (qtylosin, mg/g h) that decreased as the fermentation progressed. Continuous feeding of glutamate, glucose, and methyloleate at a constant feed rate initiated during the period of high qtylosin had been shown to produce some increase in tylosin productivity. By using a cyclic feeding strategy, it was possible to increase tylosin productivity further. Tylosin fed‐batch fermentations with glutamate and glucose being fed to the culture in cyclic square‐wave profiles with methyloleate in excess showed several‐fold increase in final qtylosin and tylosin titers. By varying cycle amplitudes and period of the substrates, it was found that maximum tylosin productivity occurred when the glutamate cycle amplitude was 600 mg/L and that of glucose was 42.5 mg/L per cycle period of 24 h. With these cycle amplitudes of glutamate and glucose, the tylosin cyclic fed‐batch culture also showed high cellular uptake of methyloleate. Decreasing or increasing glucose cycle amplitude at fixed glutamate amplitude lowered tylosin production, and no further stimulation of tylosin synthesis was observed when α‐ketoglutarate was supplemented to the cyclic substrate feeds. Under optimum cyclic conditions it was possible to maintain linear tylosin accretion and a constant value of qtylosin up to 240 h.
Prevention of formation of acid drainage from high‐sulfur coal refuse by inhibition of iron‐ and sulfur‐oxidizing microorganisms. I. Preliminary experiments in controlled shaken flasks
Authors: Dugan P. R.
Published: December 2004

Changes of pH and sulfate concentration in high‐sulfur coal refuse slurries are used as measurements of microbial pyrite oxidation in the laboratory. Sodium lauryl sulfate (SLS), alkylbenzene sulfonate (ABS), benzoic acid (BZ) and combinations of SLS plus BZ and ABS plus BZ effectively inhibited formation of sulfate and acid when added in concentrations greater than 50 mg/L to inoculated 20 or 30% coal refuse slurries. Here 25 mg/L concentrations of SLS, ABS, and ABS + BZ stimulated acid production. Formic, hexanoic, oxalic, propionic, and pyruvic acids at 0.1% concentrations were also effective inhibitors. Four different lignin sulfonates were only slightly effective inhibitors at 0.1% concentrations. It was concluded that acid formation resulting from microbial oxidation in high‐sulfur coal refuse can be inhibited.
Performance of the duckweed species Lemna gibba on municipal wastewater for effluent renovation and protein production
Authors: Oron Gideon , Porath Dan , Jansen Hans
Published: December 2004

An outdoor experiment was conducted in miniponds to evaluate the performance of Lemna gibba, a duckweed species, as a domestic wastewater stripper. Duckweed is one of the floating plants with a high capability of ammonia uptake and assimilation rate into valuable protein. The results indicate that under adequate operational conditions, depending mainly on the organic loading, the effluent quality meets irrigation reuse criteria and protein yield of the duckweed may reach 12 ton/ha per year, far above other conventional field crops.
Modeling and analysis of diffusion and reaction in legume nodules
Authors: Jones G. T. , Davis L. C. , Ghosh Hajra A. K. , Erickson L. E.
Published: December 2004

Diffusion of gases through legume nodules is important for nitrogen fixation. A mathematical model is presented for diffusion and enzymatic reaction for legume nodules with a reactive core and an inert shell. The transient model is solved numerically for spherical geometry for acetylene reduction by nitrogenase enzyme. The results are used to estimate the diffusivities of acetylene and ethylene in the nodules by comparing predicted and experimental lag times. The experimental results are also analyzed using an effectiveness factor plot for spherical nodules with inert shells and reactive cores. The results show that the diffusivities are slightly higher than those for acetylene and ethylene in water because of some contribution of gas phase diffusion. Applications to oxygen diffusion through nodule tissue are suggested.
Citric acid production using immobilized conidia of Aspergillus niger TMB 2022
Authors: Tsay S. S. , To K. Y.
Published: December 2004

Conidia of Aspergillus niger TMB 2022 were immobilized in calcium alginate for the production of citric acid. A 1‐mL conidia suspension containing ca. 2.32 × 108 conidia were entrapped into sodium alginate solution in order to prepare 3% Ca–alginate (w/v) gel bead. Immobilized conidia were inoculated into productive medium containing 14% sucrose, 0.25% (NH4)2CO3, 0.25% KH2PO4, and 0.025% MgSO4·7H2O with addition of 0.06 mg/L CuSO4·5H2O, 0.25 mg/L ZnCl2, 1.3 mg/L FeCl3·6H2O, pH 3.8, and incubated at 35°C for 13 days by surface culture to produce 61.53 g/L anhydrous citric acid. Under the same conditions with a batchwise culture, it was found that immobilized conidia could maintain a longer period for citric acid production (31 days): over 70 g/L anhydrous citric acid from runs No. 2–4, with the maximum yield for anhydrous citric acid reaching 77.02 g/L for run No. 2. In contrast, free conidia maintained a shorter acid‐producing phase, ca. 17 days; the maximum yield for anhydrous citric acid was 71.07 g/L for run No. 2 but dropped quickly as the run number increased.
A model for growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media
Authors: Sardonini Charles A. , DiBiasio David
Published: December 2004

A major problem in the use of plasmids as recombinant vectors is the problem of plasmid‐free cell generation from plasmid shedding and subsequent growth. A common technique for controlling the population of plasmidfree cells is the use of selective media against these cells using an auxotrophic host and a plasmid that has the ability to produced the essential metabolite. A distributed model describing the growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media was developed. The model allows for growth and production of a metabolite by the plasmid‐carrying strain and growth of the plasmid‐free cells on resulting metabolite concentrations. Through a determination of system constants and numerical solution to the equations, experimental batch and continuous culture results for cell concentration transients could be simulated by the model. The results indicated that despite selective pressure, plasmid‐free cell growth was significant.
Continuous production of L‐phenylalanine by transamination
Authors: Ziehr H. , Kula M.‐R. , Schmidt E. , Wandrey C. , Klein J.
Published: December 2004

L‐Phenylalanine was produced continuously from L‐as‐partate and phenylpyruvate by transaminase from a newly screened Pseudomonas putida strain. The process was carried out with an isolated enzyme in homogeneous phase in an enzyme membrane reactor and with immobilized whole cells in a stirred tank reactor, respectively. Due to the difference in transport resistance, the productivity of the free enzyme in homogeneous phase (72 mmol/L h) was about 3 times higher than the productivity achieved using immobilized cells. However, a better stability of the biocatalyst was observed with immobilized cells.
A new method to determine active enzyme distribution, effective diffusivity, rate constant for main reaction and rate constant for deactivation
Authors: Do D. D. , Hossain Md. M.
Published: December 2004

A new method is presented to determine (1) the rate constant for the main reaction, (2) the rate constant for deactivation, (3) the effective diffusivity, and (4) the active enzyme distribution within a porous solid support by utilizing data of bulk substrate concentration versus time in a continuous stirred basket reactor. The method relies on an assumption of parallel deactivation mechanism with strong pore diffusional resistance with respect to substrate species. The data of hydrogen peroxide‐immobilized catalase published in the literature are used to demonstrate the theory. A parameter determination procedure is also presented.
Kinetics of milk coagulation: I. The kinetics of kappa casein hydrolysis in the presence of enzyme deactivation
Authors: Carlson Alfred , Hill Charles G , Olson Norman F.
Published: December 2004

The kinetics of the primary phase of the enzymatic coagulation of milk, i.e., κ‐casein hydrolysis, was investigated in the presence and in the absence of concurrent enzyme deactivation processes. For conditions under which the enzyme is stable, the rate of hydrolysis can be described by Michaelis–Menten kinetics, as has been reported by previous investigators. A mathematical model, experimental data, and parameter estimates are provided for κ‐casein hydrolysis in the presence of concurrent deactivation of enzyme. The model accurately describes the experimental results when porcine pepsin was used as the renneting enzyme. The model and the experimental results indicate that samples of milk treated under conditions where deactivation of enzyme is significant can have fractional conversions of κ‐casein ranging from zero to unity and yet contain no active enzyme at the termination of the treatment.
Modeling and analysis of radial flow mammalian cell culture
Authors: Tharakan John P. , Chau Pao C.
Published: December 2004

A model for radial flow mammalian cell culture has been developed. Two situations, one with permeable hollow fibers and the other with a porous matrix in the annulus, were considered. The hollow fibers were modeled as continuously distributed sinks. Numerical solutions are presented for the complete model as well as limiting analytical solutions. The analysis identified the importance of various kinetic, transport, and design dimensionless groups for maintenance of radial flow cell culture systems under uniform conditions. The important design parameter was the depth of the bed and the important operating parameter was a modified Damkohler number, both of which should be maintained low for gradient free systems. Dispersion was included in the analysis but substrate consumption was relatively independent of dispersion. Preliminary separation of a low‐and high‐molecular‐weight product was also modeled, and shown to be strongly dependent on the permeability of the fibers, as well as the aspect ratio and the magnitude of the transmembrane flux.
Determination of the intrinsic kinetic constants of immobilized glucose oxidase and catalase
Authors: Tse Pius H. S. , Leypoldt John K. , Gough David A.
Published: December 2004

Models of membrane systems containing immobilized glucose oxidase and catalase operating together or independently have been developed. A rotated disk electrode apparatus was employed with novel electrochemical operating conditions to experimentally determine mass transfer and intrinsic kinetic parameters of enzyme‐containing membranes. The value of a mass transfer parameter that describes internal and external diffusion was first determined under conditions that do not permit the enzyme reactions. In a subsequent experiment with the reaction allowed, kinetic parameters corresponding to the intrinsic maximal velocity and Michaelis constants of the immobilized enzymes were estimated by regression analysis of data based on an appropriate two‐ or three‐ parameter model. It was found that immobilization reduced the maximal intrinsic velocity but had no detectable effect on the Michaelis constants. In all but one case‐ these methods for membrane characterization are nondestructive and can be used repeatedly on a given membrane. These techniques provide the means for quantitative comparisons of immobilization methods and make possible temporal studies of immobilized enzyme inactivation.
Time‐dependent inactivation of immobilized glucose oxidase and catalase
Authors: Tse Pius H. S. , Gough David A.
Published: December 2004

Homogeneous membranes containing immobilized glucose oxidase and catalase were stored in buffered solutions at 37°C to determine the mechanisms and rates of catalyst inactivation. The experiments were designed so that inactivation occurred homogeneously throughout the membrane, thereby simplifying the analysis. The mechanism of inactivation is consistent with the reaction of hydrogen peroxide and certain catalytic intermediates of both enzymes. Based on this information, numerical simulations were developed that incorporate spatially heterogeneous catalytic and inactivation processes.
Kinetics and bioenergetics of light‐limited photoautotrophic growth of Spirulina platensis
Authors: Lee H. Y. , Erickson L. E. , Yang S. S.
Published: December 2004

Blue–green algae, Spirulina platensis, is cultivated under photoautotrophic growth conditions designed to have nearly uniform growth rate throughout the fermentor by illumination both sides of a rectangular vessel. The results show that growth rate and bioenergetic yield are a function of light intensity. Several kinetic models are considered to express the relationship between growth rate and light intensity.
Static characteristics of a continuous flow bioreactor containing antibiotic‐resistant recombinant cells
Authors: Chang Yong K. , Lim H. C.
Published: December 2004

The steady‐state behavior of a continuous bioreactor containing antibiotic‐resistant recombinant cells has been investigated. Only the plasmid‐free cell is susceptible to and killed by antibiotics. A Monod form of specific death rate was found to simulate quite well the experimental death rates of various cells due to antibiotics. The stability characteristics, including bifurcation of the possible steady states, are examined. Appropriate numerical illustrations for the steady‐state characteristics have been provided. Theoretically, two coexistence steady states (CO), three partial washout steady states (PW), and one total washout steady state (TW) are feasible, but only one CO, one PW, and one TW were realized. When antibiotic consumption is not extremely significant the CO can exist over one or two ranges of dilution rates depending upon the antibiotic concentration in the feed. The CO is globally stable. Whenever the PW and/or the TW exist(s) together with the CO they are unstable. Sensitivity analyses for several key kinetic parameters have been made. The rate at which the plasmid‐bearing cells revert to the plasmid‐free cells has the most significant effect on the antibiotic susceptibility of the system. Some simplified optimization calculations for maximum profit have been carried out.