bluuebunny/crossref_metadata_2025 huggingface dataset:
A mathematical model of the nutrient dynamics of phytoplankton in a nitrate‐limited environment
Authors: Grenney William J. , Bella David A. , Curl Herbert C.
Published: December 2004

Insofar as saturation kinetics are applicable to the growth of phytoplankton in laboratory experiments and to growth in nature, the computer modeling of intracellular nutrient partitioning in populations of cells can lead to better understanding of the dynamics of natural populations.

A three‐compartment mathematical model was developed to represent a phytoplankton population having the capability to store nitrogen in a nitrate‐limited environment. Parameters were estimated by fitting the model to data from two chemostat experiments reported by Caperon (1968). The model was used to simulate growth dynamics observed in chemostat and batch experiments. The model demonstrated the changes which may occur in the nitrogenous constituents of a phytoplankton population with time and environmental conditions. The model also demonstrates three phenomena which have been observed in field and laboratory experiments but which are not represented by the customary Monod model: (1) uptake rates may significantly exceed not growth rates, (2) high growth rates may be encountered at very low environmental nitrate concentrations, and (3) the ratio of internal nitrogen to population size may change significantly during a study period. It is suggested that the amount of nitorgen in storage may be used as an indicator of the physiological state of a monospecific population.

Parameters for the one‐compartment Monod model were estimated by customary methods form data generated by the three‐compartment model. It was shown that difficulties encountered in estimating the yield coefficient and the decay coefficient may be attributed to the intracellular storage phenomenon. It was also demonstrated that the one‐compartment Monod model was inadequate to accurately represent population growth in chemostat experiments when intracellular storage is a significant factor.
Cell growth and extracellular enzyme synthesis in fermentations
Authors: Van Dedem G. , Moo‐Young M.
Published: December 2004

The synthesis of extracellular enzymes by microorganisms frequently occurs under genetic control. A simple two‐parameter model is developed describing the degree of repression or induction in fermentation media.

The case of substrate utilization by an extracellular enzyme was analyzed for a vegetable oil‐lipase‐yeast system. It is shown that fatty acids released by the lipase may accumulate in the early stage of growth and exert an influence on the limiting after which relatively little repression or induction takes place.

Expressions are also derived for growth and extracellular enzyme synthesis in single‐and multistage continuous cultures. When the cells grow on a directly available soluble substrate, the specific enzyme synthesis is maximal at low dilution rates in the case of repression and at high dilution rates in the case of induction. If the substrate is not directly available, a single continuous stirred tank reactor stage may not be sufficient for efficient substrate utilization; for fermentation processes where an insoluble has to be broken down before the cells can assimilate it, a plug flow type fermentor rather than a mixed chemostat may prove more satisfactory.
Mass transfer and biochemical reaction with semipermeable microcapsules
Authors: Mogensen A. O. , Vieth W. R.
Published: December 2004

Enzymes can be encapsulated within a semipermeable membrane which allows reactants to enter and the products to diffuse out. The mass transport from the external fluid to the membrane and the combined mass transport and biochemical reaction from the membrane inwards can be modeled with recognized formulations; measurements of the overall reaction rate lead then to estimates of the permeability of the membrane itself.

With capsules enclosing catalase, the permeability of collodion membranes to H2O2 is found to be large (<2 × 10−2cm/sec) in comparison to rates in the other two diffusion zones. For this first‐order reaction system, an analytical solution to the transient case of the well‐stirred finite bath is found using the Laplace transform. With capsules enclosing urease, the nonlinear Michaelis‐Menten kinetics apply to the enzymatic step. The steady‐state operation of a column packed with urease microcapsules is analyzed with the aid of numerical computation and the membrane permeability for urea is found to be 10−3cm/sec.
An apparatus to measure the rate of oxygen evolution while maintaining pO2 constant during photosynthetic growth in closed culture vessels capable of operation at increased hydrostatic pressures
Authors: Pope D. H. , Berger L. R.
Published: December 2004

A double polarographic device is described which permits regulation of dissolved oxygen concentration at any preset pO2 in suspensions or cultures of photosynthetic algae. It also simultaneously permits measurements of the rate of oxygen evolution during photosynthesis. The apparatus is designed to operate in closed vessels in the absence of a gas phase, and may be used at increased pressures tested up to 500 atmospheres. Regulation of oxygen levels was maintained constant at various preset concentrations equivalent to atmospheric pO2 values ranging between 0.02 and 0.21 at 25°C.
Immunochemical characterization of commercial protease products
Authors: Hodson P. H. , Scharpf L. G.
Published: December 2004

Total protease activity at pH 7 and 10.3 of 23 commercial grade enzymes was determined. The type and amount of enzymatic activity varied widely among the products. The wide variation in pH 7.0/pH 10.3 proteolytic activity ratios among products indicated that the products studied contained differing levels of alkaline and neutral proteases.

Antisera were prepared against the purified enzyme in detergent grade Enzyme AP, neutral protease from B. megaterium, detergent grade ALK Enzyme, and Thermolysin. The commercial (unpurified) products were classified as neutral subtilopeptidase A and subtilopeptidase B from three Bacillus species using these antisera.

It was concluded that standard immunochemical techniques provide rapid and sensitive methods for the preliminary identification of sources and types of proteases present in commercial enzyme products.
Phospholipase‐C from Bacillus cereus: Production, purification, and properties
Authors: Shiloach J. , Bauer S. , Vlodavsky I. , Selinger Z.
Published: December 2004

A substrain of Bacillus cereus 569/H produced under controlled fermentation conditions in a pilot plant fermentor phospholipase‐C. A partially purified preparation showed good storage stability as a lyophylized powder and in frozen solutions. The preparation contained very small amounts of phosphomonoesterase and proteolytic activities and essentially no ribonuclease activity. The level of hemolytic activity of the preparation was much lower than that of a commercial preparation of phospholipase‐C from Clostridium. Treatment of sarcoplasmic reticulum membrane with phospholipase‐C from B. cereus and from Clostridium showed that the B. cereus enzyme caused hydrolysis of 96% of the membrane phospholipids whereas the enzyme from Clostridium could hydrolyze only 80% of the phospholipids.
Evaluation of ultrafiltration membranes with biological macromolecules
Authors: Hancher C. W. , Ryon A. D.
Published: December 2004

Eighteen ultrafiltration membranes ranging in molecular weight cutoff ratings from 500 to 300,000 were tested with water, 0.5M NaCl solution, and, in some cases, with macromolecules and urea in a 3‐in. stirred filter cell. Approximately half of the membranes showed a significant decrease in filtration rate during the first 24‐hr period. The steady‐state rates were less than the manufacturers' rating for about two thirds of the membranes, the discrepancy being greater for the membranes with high molecular weight cutoffs.

The filtration rates were linearly dependent on applied pressure over the range at least as great as 15 to 55 psig. The rate decreased as the concentration of macromolecules such as transfer ribonucleic acid (tRNA) increased; the rate for a concentration of 3 mg tRNA/per ml was one‐fourth of that observed when no tRNA was present. Some increase in rate (∼33 to 50%) was obtained by increasing the stirring speed from 100 rpm to 1000 rpm.

The membranes were effective for desalting and concentration of macromolecules but not for separation of large molecules from each other, such as tRNA from bovine serum albumin. Easily denatured molecules such as catalase were not deactivated by filtration at 4°C.
An extreme pressure pump for continuous cell disintegration
Authors: Brookman James S. G. , Davies Maldwyn
Published: December 2004

The use of an air operated extreme pressure hydraulic pump for continuous cell disintegration is described, together with figures obtained for soluble protein released from suspensions of commercially obtained baker's yeast (Saccharomyces cerevisiae).
Oxygen absorption in stirred tanks: A correlation for ionic strength effects
Authors: Robinson Campbell W. , Wilke Charles R.
Published: December 2004

A new correlation is given for the prediction of the volumetric coefficient for mass transfer (KLa) in stirred tanks from dispersed gas bubbles to basal salt solutions of ionic strengths representative of fermentation media. The correlation includes the effects of both the operating parameters (agitation power per unit volume and gas superficial velocity) and the physicochemical properties of the system: interfacial tension, viscosity, density, diffusion, coefficient and, in particular, ionic strength. The effect of the latter was found to be most significant in the Newtonian systems of water‐like viscosity investigated; no previous correlations have included the effect of ionic strength. KLa values were determined by using a dissolved oxygen probe to monitor the steady‐state oxygen tension in continuous flow experiments, and/or the rate of change of oxygen tension in unsteady‐state semibatch experiments. In the latter cases, results were computed by a nonlinear, least squares computer program which fitted the experimental data to a model of probe transient response characteristics. The general applicability of the model and the computational procedure was verified by comparing the results to those obtained with the same electrolyte solution in the steady‐state mode. The experiments were run over a wide range of agitation power inputs, including those typical of both soluble‐ and insoluble‐substrate fermentations. The correlation appears to be valid for both oxygen mass transfer with and without homogeneous chemical reaction in the liquid phase; in the former case, for example, sulfite oxidation, knowledge of the chemical reaction enhancement factor is required. In addition to predicting oxygen transfer capabilities, the correlation may be used for other sparingly soluble gases of interest in fermentation systems, such as methane, hydrogen, and carbon dioxide.
Production of microbial protein from waste cellulose by Thermomonospora fusca, a thermophilic actinomycete
Authors: Crawford Don L. , McCoy Elizabeth , Harkin John M. , Jones Paula
Published: December 2004

The growth characteristics of Thermomonospora fusca, a cellulolytic thermophilic actinomycete, are described in terms of growth on pulping fines, a cellulosic waste of the paper industry. A fermentation was developed which substantially degrades this waste, with the residual product of growth containing about 30% microbial protein. This protein, as shown by a preliminary feeding study with baby chicks and by amino acid analyses, appears to be of good nutritional quality and contains no strongly toxic materials. The extracellular cellulolytic enzymes present in the spent broth are discussed in relation to their potential recovery as a by‐product of the fermentation, as is also the possible use of the fermentation as a waste disposal system.
Mixing by impeller agitation in continuous flow systems containing polysaccharide solutions
Authors: Johnson D. N. , Hubbard D. W.
Published: December 2004

System response data for step changes in input tracer concentration have been obtained for two different impeller agitated continuous flow mixing systems containing aqueous polysaccharide solutions. The vessel volumes were 1.6 and 10.9 liters. Polysaccharide concentration, dilution rate, and impeller speed were varied according to a plan devised using dimensional analysis and assuming that bulk motion is the predominant mass transport mechanism in the system. The data show that this is not true and that serious errors may occur if scale‐up calculations are based on assuming that bulk motion predominates. Under the operating conditions used, perfect mixing was not observed.
Application of an insolubilized hepatic microsomal drug oxidase to the continous production of N‐oxides
Authors: Sofer Samir S. , Ziegler Daniel M. , Popovich Robert P.
Published: December 2004

The optimum operating temperature and pH have been determined for a catalyst prepared by the insolubilization of a hepatic microsomal mixed‐function oxidase on glass beads. Temperature is a more significant variable than pH in determining potential catalyst yield (total product/unit catalyst). An operating range of about 25–28°C is optimal with respect to catalyst life at pH 7.6. Like the purified soluble oxidase, the glass bead‐mounted enzyme catalyzes the NADPH‐ and oxygen‐dependent oxidation of a variety of amines, hydrazines, and thioureylenes. The catalyst has been used in a simple slurry reactor to prepare mg quantities of N‐oxide metabolites of prochlorperazine, guanethidine, and ethylmorphine.
High‐yield growth of E. coli at different temperatures in a bench scale fermentor
Authors: Shiloach J. , Bauer S.
Published: December 2004

E. coli wax grown exponentially at different temperatures in a bench scale fermentor. pH was maintained at 6.8 by ammonia which served also as the nitrogen source. Glucose was introduced semi‐continuously at a predetermined rate which ensured a glucose concentration of 25–50 g/liter during growth. The culture was sparged with pure oxygen.

Yield constants for glucose, nitrogen, phosphorus, and oxygen were determined at the different temperatures of propagation.

When all growth conditions, except temperature, were kept constant, the maximal possible yield of exponentially grown cell mass was found to be directly proportional to the doubling time. Concentrations of up to 55 g dry cells/liter culture were achieved.
Kinetics of substrate inhibition of exponential yeast growth
Authors: Jackson Jay V. , Edwards Victor H.
Published: December 2004

This work concerns mathematical modeling of the rate of microbial growth on inhibitory levels of nutrients as affected by pH, concentration of the nutrients, temperature, cultivation method, and method of data analysis. Candida utilis (ATCC 9226) was grown with sodium acetate as growth‐limiting carbon and energy source in mineral salts medium in shake flask and continuous cultures to study inhibition by excess acetate. Differential shake flask cultures were grown at low yeast concentrations at temperatures (T) of 25 and 30°C, pH's between 5.5 and 7.0, and acetate concentrations (S) between 0.25 and 3.0% (w/v). Growth data were exponential with correlation coefficients greater than 0.995 in 49 of 56 experiments; the lowest correlation coefficient was 0.986. Specific growth rates (μ) determined by graphical methods showed only fair correlation with those determined by regression analysis. Both sets of specific growth rate data were grouped at constant T and pH and fitted to the three parameter equation,

The improvement in use of the fitted equation instead of the mean value was significant with greater than 70% confidence in all (14 groups) and 90% confidence in only half of the data groups; the correlation does not improve with the increasing acetate inhibition at lower pH. Both defects in the model and insufficient data at each pH are responsible. A modified six parameters with hydrogen ion concentration(H+) as follows:

Specific growth rates calculated with the six parameter equation matched observed values in all groups of isothermal data better than the means with greater than 99% confidence. The six parameter model adequately represents effects of acetate and hydrogen ion concentrations under constant or slowly changing environmental conditions and balanced growth; although better models probably exist. Thus steady‐stste and transient continuous culture experiments agreed with many published growth yields, but specific growth rates could only be predicted qualitatively from the model fit to the shake flask data. The data and present models could be incorporated into published models for transient growth at low nutrient concentrations to correlate and perhaps predict microbial growth kinetics over a much wider range of growth conditions than now possible.
Continuous lactic acid fermentation of whey to produce a ruminant feed supplement high in crude protein
Authors: Keller A. Kent , Gerhardt Philipp
Published: December 2004

A mathematical model was developed to simulate, on a digital computer, the continuous fermentation of whey lactose to lactic acid with neutralization by ammonia. The simulation predicted the retention times for experimental test and the use of two stages for greatest efficiency. In the experimental tests, Lactobacillus bulgaricus was inoculated into whey in a 14‐liter continuous fermentor at 44°C and with automatic pH control. A series of steady‐state conditions was managed nonaseptically for 42 days without evident contamination and with an actual increase in the efficiency of conversion. Lactic acid was produced predominately' throughout the period, with less than 0.2% of other compounds. The product contained approximately 8 times as much crude protein (N × 6.25) as the original whey. In a single‐stage fermentation at pH 5.5, a retention time of 15 hr resulted in a residual lactose concentration of 0.7%; and little improvement was realized by increasing the retention time. Increasing the pH to 5.8 resulted in a significant improvement, but further increasing the pH to 6.0 resulted in only a small additional gain. By the employment of two fermentors in series at pH 5.5 with a total retention time of 31 hr, the residual lactose was reduced to less than 0.1%. Lactic acid was produced as a function mainly of maintenance rather than growth metabolism.
A multigroup model for predator‐prey interactions
Authors: Villarreal Ernesto , Canale Raymond P. , Akcasu Ziya
Published: December 2004

The predator‐prey interactions between the protozoan Tetrahymena pyriformis and the bacterium Aerobacter aerogenes have been studied experimentally and mathematically. A mathematical model for the ciliates defines the mass distribution of cells within the population. The resulting model equations are solved by the use of multigroup theory. Experimental data from batch and continuous flow reactors are compared with the results of the numerical integration.
Adsorption of amyloglucosidase on inorganic carriers
Authors: Solomon B. , Levin Y.
Published: December 2004

A simple method for immobilizing amyloglucosidase by adsorption on inorganic carriers is described. Amyloglucosidase was adsorbed on acid‐activated molecular sieve and on alumina. The immobilized enzyme preparations exhibited 50–100% of the initial activity and possessed high temperature stability. A prolonged working life span was achieved, which could possibly satisfy requirements for industrial application.
YATP value in Candida tropicalis grown on n‐alkanes, fatty acids, and acetate
Authors: Gallo Michel , Azoulay Edgard
Published: December 2004

The amount of ATP produced during n‐alkane, fatty acid, or acetate metabolism in Candida tropicalis has been established from the P/O ratios measured on isolated mitochondria, yield on substrate andcarbon balance. For these three kinds of substrates, YATP value has been found to be close to 4, although Ysub on acetate is very different from those found with n‐alkanes or fatty acids.
Performance of affinity chromatography columns
Authors: Katoh Shigeo , Kambayashi Tomio , Deguchi Ryuichi , Yoshida Fumitake
Published: December 2004

Performance of affinity chromatography columns was studied by measuring the rates of adsorption and elution of trypsin in a Sepharose 4B‐soybean trypsin inhibitor column and a Sepharose 4B‐arginine peptides column. The volumetric coefficient for trypsin transfer was evaluated from the break‐through curves of trypsin, and elution profiles bed height of Sepharose 4B‐STI column was estimated based on these results.
Chemical flocculability of sludge organisms in response to growth conditions
Authors: Wu Yeun C.
Published: December 2004

The effect of waste characteristics on the removal of suspended solids and soluble phosphorus by alum, Al2(SO4)3·18H2O, was investigated in an activated sludge system with no cellular recycle. Under the conditions presently studied, it was found that sludge organisms grown in nitrogen‐ and phosphorus‐restricted media possess exceptionally large capsules and produce a higher surface electric charge per unit of fry weight. Chemical demand for separation of these capsulated cells is obviously higher than those solids cultivated under a well‐balanced nutrient condition. For phosphorus removal, the molar ratio of Al+3:P is a function of the initial concentrations of soluble phosphorus and suspended solids in solution. The relationship between percent phosphorus removal and the quantity of chemical coagulent used shows nonstoichiometric relationship; that is, the required molar ratio of Al+3:P is always greater than one and directly depends upon the content of suspended solids in the flocculated media. Moreover, the present study indicated that chemical separation of dispersed microorganisms occurred following phosphorus removal.
Mycelial paper: A potential resource recovery process?
Authors: Johnson Morris A. , Carlson John A.
Published: December 2004

Eleven species of fungi representative of a broad range of cell‐wall compositions were evaluated with respect to their papermaking potential as additives to woodpulp furnishes. Some of these species were also examined for their ability to grow on a spent liquor from the pulp‐and‐paper industry. Handsheets with various levels of incorporated mycelia exhibited a wide range of species‐dependent properties. Behavior of the mycelia in the sheets can be modified to a degree by physical and chemical treatments. The overall results suggest that small amounts (5–10% of the sheet constituents) of mycelia, grown inexpensively on waste effluents, might be incorporated into wood fiber paper without serious deleterious effects on paper strength properties. In some cases improved paper is obtained, and larger quantities of mycelia might be used to impart specific properties to the product.
Applications of purification reactions for minimizing reaction‐generated enzyme poisoniong
Authors: Yeung Simon Y. S. , Cho Yong K. , Bailey James E.
Published: December 2004

A mathematical model has been employed to examine the interplay of reaction and mass transfer in immobilized enzyme systems involving reaction‐generated enzyme poisons. Deactivation rates can be significantly reduced in some cases by catalyzing a purification reaction in which the poison is transformed into an innocuous substance. This conclusion is illustrated experimentally for reaction‐generated H2O2 in a continuous‐flow stirred slurry reactor containing glucose oxidase immobilized on activated carbon.
Steroid transformation by activated living immobilized Arthrobacter simplex cells
Authors: Ohlson S. , Larsson P. O. , Mosbach K.
Published: December 2004

A preparation of living Arthrobacter simplex cells immobilized in polyacrylamide gel, which showed steroid‐Δ1‐dehydrogenase activity, was studied. The entrapped microorganisms catalyzed the transformation of cortisol to prednisolone and this reaction was followed spectrophotometrically or with the aid of thin layer chromatography (TLC) and high pressure liquid chromatography (HPLC). About 40% of the original activity found with free bacteria was retained after immobilization. The steroid dehydrogenase activity of polyacrylamide‐entrapped A. simplex could be raised to a minor extent in alcoholic solvents or by addition of a cofactor such as menadione. On incubation in various nutrient media, on the other hand, the activity could be increased considerablyl, usually 7–10 times. Possible causes for the observed increase in activity have been investigated, and microbial growth of the original entrapped microorganisms appears to be the major reason. Frozen activated preparations of immobilized A. simplex showed only a small loss of activity on storage for at least four months. A semicontinuous batch wise operation with immobilized A. simplex in different nutrient media was carried out. At the end of the experiment the steroid transformation capacity was 0.5 g steroid per day per g gel (wet weight).
Immobilization of amyloglucosidase on poly [(glycidyl methacrylate) Co(ethylene dimethacrylate)] carrier and its derivatives
Authors: Švec F. , Kálal J. , Menyailova I. I. , Nakhapetyan L. A.
Published: December 2004

Immobilization of amyloglucosidase (EC 3.2.1.3) from Endomycopsis bispora and Aspergillus niger was followed with carriers containing epoxide, aldehyde, and primary amino groups. Determinations of stability of bound enzyme showed that the most active and stable preparations were obtained by application of the carrier with amino groups activated with glutaraldehyde (activity half‐life 96.6 days). Optimum pH and and temperature were found for cleavage of starch solution and KM(app) and Vmax(app) values were determined for all prepared samples.
Maintenance requirements for bacteria growing on C1‐compounds
Authors: Rokem (Rock) J. S. , Goldberg I. , Mateles R. I.
Published: December 2004

The maintenance coefficient, ms (mmol substrate/g cell dry wt hr), of two distinct groups of C1‐utilizing bacteria has been determined by growing the organisms in an aerobic continuous culture limited by different C1 growth substrates. For growth on methanol, ms = 2.5 ± 0.3 for Pseudomonas C; 3.9 ± 0.7 for Ps. methylotropha (these bacteria utilize methanol via the ribulose monophosphate pathway of formaldehyde fixation) 1.5 ± 0.2 for Pseudomonas 1, and 2.3 ± 0.4 for Pseudomonas 135 (the latter bacteria utilize C1‐compounds via the serine pathway). For growth on formaldehyde, ms = 1.5 ± 0.3 for Pseudomonas 1 and 2.7 ± 0.7 for Pseudomonas 135, whereas on formate the values for ms are 1.0 ± 0.2 and 4.4 ± 1.3; respectively. Although the maintenance coefficients did not differ systematically between the two groups of bacteria, the maintenance requirements per generation of the serine pathway bacteria were considerably higher (8.7 vs. 3.9) owing to their slower growth rate. The maximum molar yield values, YMmax (g cell dry wt/mol substrate utilized), corrected for the maintenance energy of bacteria which utilize C1‐compounds via the ribulose monophosphate pathway averged 10.1 when grown on methanol, while the values for bacteria which use the serine pathway averaged 13.5. On formaldehyde an average value of 11.5 is obtained and on formate the average value was 7.4 in the serine pathway bacteria.
Application of mass and energy balance regularities in fermentation
Authors: Erickson L. E. , Minkevich I. G. , Eroshin V. K.
Published: December 2004

Material and energy balances for fermentation processes are developed based on the facts that the heat of reaction per electron transferred to oxygen for a wide variety of organic molecules, the number of available electrons per carbon atom in biomass, and the weight fraction carbon in biomass are relatively constant. Mass–energy balance equations are developed which relate the biomass energetic yield coefficient to sets of variables which may be determined experimentally. Organic substrate consumption, biomass production, oxygen consumption, carbon dioxide production, heat evolution, and nitrogen consumption are considered as measured variables. Application of the balances using direct and indirect methods of yield coefficient estimation is illustrated using experimental results from the literature. Product formation is included in the balance equations and the effect of product formation on biomass yield estimates is examined. Application of mass–energy balances in the optimal operation of continuous single‐cell protein production facilities is examined, and the variation of optimal operating conditions with changes in yield are illustrated for methanol as organic substrate.
Modeling the role of cyclic AMP in catabolite repression of inducible enzyme biosynthesis in mircobial cells
Authors: Gondo Shinichiro , Venkatasubramanian K. , Vieth Wolf R. , Constantinides A.
Published: December 2004

Modeling the role of cyclic AMP (cAMP) in catabolite repression of inducible enzyme production in microbial cells was studied. A catabolite repression index, F, was defined based on the postulation that complex formation occurs between RNA polymerase (RNAP) and DNA, and shifting from the inert form to the open form of this complex (the latter form is required for transcription) is accelerated by the cAMP·CRP complex. The catabolite repression index, F, was incorporated into model equations of mRNA production. Empirical relationship between intracellular cAMP level and medium glucose concentration were established based on experimental data and introduced into the model. Computer simulation results were obtained for a number of interesting cases. The practical utility of the proposed model was demonstrated by comparing it with the experimental results on glucose isomerase biosynthesis.
Diffusional influences on the parametric sensitivity of immobilized enzyme catalysts
Authors: Karanth N. G. , Bailey J. E.
Published: December 2004

Immobilization of an enzyme within an insoluble material permeable to substrate can change the apparent behavior of the enzyme. In particular, external mass transfer and intraparticle diffusion effects can significantly influence the dependence of observed reaction rate on operating parameters such as temperature and pH. This analysis shows that, under very general conditions, the influence of diffusion alone is to diminish the sensitivity of the observed rate to any parameter that is uniform throughout the catalyst particle. However, the optimal value of the parameter is not changed because of intrapellet diffusional effects.
Comparison of maximum cell yield and maintenance coefficients in axenic cultures and activated sludge communities
Authors: Pipyn P. , Verstraete W.
Published: December 2004

Comparison of the equations that describe the relationship between the maximum cell yield coefficient, the maintenance coefficient, and the specific growth rate at steady‐state conditions revealed that the equations used for axenic cultures are congruent with those commonly used for mixed‐culture system such as activated sludge. A unified basis was proposed. The expression of the yield and maintenance coefficients in carbon units according to the unified basis permitted one to evaluate literature data on both axenic and mixed‐culture systems. From this it appears that the maximum cell yield ranges from 0.50–0.80 (mg biomass carbon formed/mg substrate carbon used) for both axenic and mixed systems. However, the maintenance coefficient (mg substrate C/mg biomass C·hr) for the axenic cultures was between 0.010 and 0.100, but for activated sludge communities it was between 0.001 and 0.010. Microorganisms were isolated from sludge communities with these apparently low maintenance requirements and grown axenilly. Their maintenance coefficients but not their maximum yield coefficients decreased with decreasing specific growth rates. The consequences of this finding with regard to species selection in mixed‐culture systems and the concept of cellular maintenance requirement are discussed.
Immobilization of Streptomyces phaerochromogenes by radiation‐induced polymerization of glass‐forming monomers
Authors: Kumakura Minoru , Yoshida Masaru , Kaetsu Isao
Published: December 2004

Immobilization of Streptomyces phaerochromogenes was radiation induced polymerization of 2‐hydroxylate at low temperatures. Radiation damage of the enzyme could be avoided by choosing irradiation at low temperatures. The enzymatic activity of immobilized cells increased remarkably with a decrease in the irradiation temperature of about −24°C. In constrast to the case of cell‐free enzyme immobilization, the most characteristic case was that in these immobilized cells, the enzymatic activity did not decrease with repeated use even in the composite obtained at much lower monomer concentrations. Another characteristic of immobilized cells was the increase in enzymatic activity in the initial stage of repeated use, which could be attributed to the swelling effect of the polymer matrix, thereby increasing the enzymatic activity to whole cells.
Energetic efficiency of biomass and product formation
Authors: Erickson L. E.
Published: December 2004

Equations are developed that may be used to estimate the energetic efficiency of biomass production and product formation when organic substrate consumption is used for growth, maintenance, and product formation. Regularities are utilized to develop balance equations with which the energetic efficiencies of biomass production and product formation may be estimated using several different sets of measured variables. The theory is illustrated by considering the growth in continuous culture of Aspergillus nidulans, which produces melanin.
Enzyme immobilization techniques on poly(glycidyl methacrylate‐co‐ethylene dimethacrylate) carrier with penicillin amidase as model
Authors: Drobník J. , Saudek V. , Švec F. , Kálal J. , Vojtíšek V. , Bárta M.
Published: December 2004

Two types of bead‐form macroporous carriers based on glycidyl methacrylate with ethylene dimethacrylate copolymers were used for the immobilization of penicillin amidase either directly or after chemical modificaton. Direct binding through oxirane groups, which is equally efficient at pH 4.2 and 7, is relatively slow and brings about an activity loss at low enzyme concentrations. The most efficient immobilization was achieved on glutaraldehyde‐activated amino carier, irrespective of whether the amino groups were formed by ammonia or 1,6‐diaminohexane treatment of the original oxirane carrier. Hydrazine treatment gave lower immobilization yields. The same is true of the azide method independent of the length of the spacer. Most enzyme activity was preserved by coupling the carbodiimide‐activated enzyme to the carrier with alkyl or arylamino groups at the end of a longer substituent. Immobilization on diazo‐modified carrier gave average results. Rapid immobilization by a lysine‐modified phosgene‐treated carrier resulted in an activity loss. It is suggested that multipoint and very tight attachment of the enzyme molecule to the matrix decreased the activity. The immobilized activity is quite stable in solution and very stable upon lyophilization with sucrose.
Microbial electrode sensor for alcohols
Authors: Hikuma Motohiko , Kubo Tatsuru , Yasuda Takeo , Karube Isao , Suzuki Shuichi
Published: December 2004

A microbial electrode consisting of immobilized microorganisms, a gas permeable Teflon membrane, and an oxygen electrode was prepared for the continuous determination of methyl and ethyl alcohols. Immobilized Trichosporon brassicae was employed for a microbial electrode sensor for ethyl alcohol. When a sample solution containing ethyl alcohol was injected into a microbial electrode system, the current of the electrode decreased markedly with time until a steady state was reached. The response time was within 10 min by the steady state method and within 6 min by the pulse method. A linear relationship was observed between the current decrease and the concentration of ethyl alcohol below 22.5 mg/liter. The current was reproducible within ± 6% of the relative error when a sample solution containing 16.5 mg/liter ethyl alcohol. The standard deviation was 0.5 mg/liter in 40 experiments. The selectivity of the microbial electrode sensor for ethyl alcohol was satisfactory. The microbial electrode sensor was applied to a fermentation broth of yeasts and satisfactory comparative results were obtained (correlation coefficient 0.98). The current output of the microbial electrode sensor was almost constant for more than three weeks and 2100 assays. A microbial electrode sensor using immobilized bacteria for methyl alcohol was also described.
Feedback control of a competitive mixed‐culture system
Authors: Wilder Carl T. , Cadman Theodore W. , Hatch Randolph T.
Published: December 2004

Three feedback strategies for the on‐line control of cell densities in a mixed‐culture system have been examined. A competitive mixed‐culture system of Candida utilis and Corynebacterium glutamicum grown on glucose as the limiting carbon source was modeled using Monod growth kinetics. First‐order time constants were added to simulate transient growth effects. Multivariable feedback control of cell densities by manipulation of substrate feed and dilution rate was investigated. Feedback strategies directed to minimizing control interactions were found to be superior to classical feedback. Transients in the growth‐rate response produced oscillations in cell density and required retuning of control constants. The relative time constants of the two species were important, with the largest oscillations resulting when the faster growing organism had the faster time constant.
Model of growth and ergot alkaloid production by Claviceps purpurea
Authors: Grm B. , Mele M. , Kremser M.
Published: December 2004

A growth model for Claviceps purpurea in submerged batch culture is presented. In developing the model, the basic principles of the growth and the morphological properties of C. purpurea are considered. The growth of C. purpurea is assumed to occur in a three‐step manner; the first step involves the assimilation and the growth of cells; the second one involves cell division, and the third one involves transformation of the mature cells to a state where they have no ability to divide but do have the ability to produce ergot alkaloids and then they gradually die. Inorganic phosphate is assumed to be the limiting substrate for the first and the second steps in conditions of carbon source being in excess. The model constants are determined by model simulation and graphical searching techniques to find the minimum value of the absolute difference between the experimental and the simulated curves for biomass, alkaloids, and sucrose.
Temperature and pH dependence of mold α‐galactosidase
Authors: Kobayashi Harumi , Suzuki Hideo
Published: December 2004

The effect of temperature and pH on kinetic behavior of α‐galactosidase of Mortierella vinacea was investigated on the hydrolysis of p‐nitrophenyl‐α‐D‐galactopyranoside (PNPG). A very unusual kinetic behavior was observed for the soluble α‐galactosidase i.e., substrate inhibition diminished gradually with increasing temperature or near the neutral pH range, and the kinetics approached the ordinary Michaelis‐Menten (MM) type. On the other hand, with decreasing temperature or in acidic pH range, substrate inhibition was accelerated. Therefore, Arrhenius plots based on the initial reaction rate did not give straight lines. Furthermore, the slope in the Arrhenius plot changed with substrate concentration, which would make the determination of a characteristic value using conventional methods meaningless. However, the Arrhenius plots of individual kinetic parameters in the rate equation resulted in straight lines in the temperature range 15 to 50°C. From this, the drastic change in kinetic behavior could be explained in connection with the temperature and pH dependence of kinetic parameters in the model. For mold pellets (whole‐cell enzyme), however, the influence of temperature and pH was less apparent than that of soluble enzyme because of the limitation in intraparticle diffusion. By using the rate equation that was determined for soluble enzyme and the theoretically derived effectiveness factor, the overall reaction rate for mold pellets at various temperature and pH could be predicted to some extent.
Growth of yeast on n‐alkanes. I. Stochastic model
Authors: Verkooyen A. H. M. , Rietema K.
Published: December 2004

In a system where yeast cells grow on n‐alkanes dissolved in oil drops suspended in water, the dispersed oil phase will, in most cases, be fully segregated. This means that each drop has its own history that depends on its degree of saturation with yeast cells. This degree of saturation with yeast cells is determined by a stochastic process depending on adsorption, desorption, and cell production. Although many authors mention segregation as a phenomenon likely to occur, so far this segregation has hardly been taken into account. In this paper the interaction of the population of completely segregated oil drops with the population of yeast cells, which results in growth, is described. The consequences of the model are elucidated by the discussion of some extreme cases. The batch fermentation of hydrocarbons by yeast cell is simulated by means of a Monte Carlo procedure. Adsorption, desorption, and production of yeast cells are considered as chance processes. The history of all individual drops is recorder. The influence of the chance of desorption appears to be much larger than that of the chance of adsorption (at the investigated range). Also the size of the inoculum at the start of the process appears to have a strong influence on the course of fermentation.
Growth of yeast on n‐alkanes. II. Adsorption‐ desorption phenomena
Authors: Verkooyen A. H. M. , van den Oever A. H. C. , Rietema K.
Published: December 2004

In the stochastic as well as in other models that describe the growth of yeast on liquid hydrocarbons, the adsorption and desorption of cells to drops influence to a very great extent the growth rate of the cells. In this paper a method is presented and equipment is described by which it was possible to measure the cell‐drop interaction directly. While analyzing the results of these measurements it was found that the adsorption and desorption of cells are rather complicated processes. The size distribution of the oil drops is one of the parameters that has to be taken into account. The analysis of the results yields a fairly accurate value for the initial adsorption rate. Departing from a somewhat speculative description of the influence of drop size distribution on the adsorption rate, the order of magnitude of the desorption rate constant could be calculated.
Use of the upflow sludge blanket (USB) reactor concept for biological wastewater treatment, especially for anaerobic treatment
Authors: Lettinga G. , van Velsen A. F. M. , Hobma S. W. , de Zeeuw W. , Klapwijk A.
Published: December 2004

In recent years considerable effort has been made in the Netherlands toward the development of a more sophisticated anaerobic treatment process, suitable for treating low a strength wastes and for applications at liquid detention times of 3–4 hr. The efforts have resulted in new type of upflow anaerobic sludge blanket (UASB) process, which in recent 6 m3 pilot‐plant experiments has shown to be capable of handling organic space loads of 15–40 kg chemical oxygen demand (COD)·m−3/day at 3–8 hr liquid detention times. In the first 200 m3 full‐scale plant of the UASB concept, organic space loadings of up to 16 kg COD·m−3/day could be treated satisfactorily at a detention times of 4 hr, using sugar beet waste as feed. The main results obtained with the process in the laboratory as well as in 6 m3 pilot plant and 200 m3 full‐scale experiments are presented and evaluated in this paper. Special attention is given to the main operating characteristics of the UASB reactor concept. Moreover, some preliminary results are presented of laboratory experiments concerning the use of the USB reactor concept for denitrification as well as for the acid formation step in anaerobic treatment. For both purposes the process looks feasible because very satisfactory results with respect to denitrification and acid formation can be achieved at very high hydraulic loads (12 day−1) and high organic loading rates, i.e., 20 kg COD·m−3/day in the denitrification and 60–80 kg COD·m−3/day in the acid formation experiments.
Kinetic behavior of immobilized Penicillin acylase
Authors: Carleysmith S. W. , Dunnill P. , Lilly M. D.
Published: December 2004

Penicillin acylase has been immobilized to carboxymethylcellulose and to the resin Amberlite XAD7. The reaction kinetics of the enzyme were affected by both intrinsic (molecular) and microenvironmental effects. The Michaelis constant for the enzyme increased after immobilization as a result of an intrinsic effect of the reagent, glutaraldehyde, used for enzyme immobilization. Microenvironmental effects were of two types: diffusional limitation of access of substrate and a reaction‐generated pH depression in the support particles. This depression of internal pH was observed in all the preparations and could be reduced by addition of pH buffering salts to reactor. An adsorbed pH‐indicating dyc was used to determine the surface and internal pH of particles of XAD7–penicillin acylase under various reaction conditions. The extent of diffusional rate limitation in XAD7–penicillin acylase was related to the penetration depth of protein into the porous support particles. The penetration depth of protein and thus the diffusional limitation of the reaction rate could be controlled by the conditions of preparation of the immobilized enzyme. A staining technique was used to observe the location of the protein.
Extracellular microbial polysaccharides. II. Evolution of broth Power‐law parameters for xanthan and pullulan batch fermentation
Authors: Thomson Norman , Ollis David F.
Published: December 2004

The shear viscosities of xanthan batch fermentation broths obey a power‐law relation τ = K (P)[ẏ]N(P), where the power‐law parameters are functions of xanthan concentration P. within the shear rate range of 1.15 to 384.0 sec−1. Cell‐free solutions prepared from these samples exhibit the same values of K and N as the corresponding cell‐bearing broth. Further, in the course of the fermentation time, t, it was found that K(P) and N(P) were related by an equation of the form ln K[P(t)] = ln τ0 – N[P(t)]·ln ẏ0, leading to a dimensionless power‐law equation valid over the entire fermentation: (τ/τ0) = (ẏ/ẏ0)N[P(t)]. The resulting power‐low from[(τ/τ0) = [ẏ/ẏ0]N(t)] indicates that all related samples will exhibit power‐low plots passing through the common point, (τ0γ0). These equations have previously been observed with other polysaccharide solution. They are also shown here to be applicable to the pullulan fermentation data of Leduy et at. The parameter K is related to polymer concentration (P) with the correlation K = A PB, where B = 1.75 ± 0.25 for xanthan solutions. With X(t), S(t), and P(t) available from paper I, the correlations of this paper (hereafter referred to as II) [K(t) = f(P)(t) and N(t) = g(K(t))] provide a predictive description of the shear viscosity evolution of polysaccharide‐producing fermentation broths.
Yield regulation of lysine biosynthesis in Brevibacterium flavum
Authors: Shvinka J. , Viesturs U. , Ruklisha M.
Published: December 2004

A scheme for lysine biosynthesis using variants of the Brevibacterium flavum intermediary metabolite synthesis is discussed. The main precursor of lysine that we are concerned with here is oxalacetate, which can be synthesized through the TCA or glyoxylate cycles or by carboxylation of PEP. Material energy balances for the main pathways of lysine biosynthesis from glucose and acetate have been formulated. Energy consumption, in the from of ATP – PATP (number of mol ATP consumed/1 mol lysine synthesized), was calculated for the main pathways of lysine biosynthesis. Theoretical conversion yields Ypmax (g product/g substrate) were estimated. Experimental data were presented concerning the increase of Yp by means of metabolism regulation: (a) by TCA‐and glyoxylate‐cycle enzyme induction; (b) by maintaining PEP carboxylase activity; (c) by eliminating by‐product synthesis.