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Showing papers in "Biotechnology and Bioengineering in 1970"


Journal ArticleDOI
TL;DR: Comparison of results obtained in continuous culture with results from exponential‐feed culture systems is shown to offer a novel experimental method for evaluating the effect of the cell age distribution on the properties and metabolic activity of a culture.
Abstract: High substrate concentrations inhibit growth and may distort the metabolism of microorganisms. Mechanisms causing substrate inhibition are discussed and used to derive several mathematical models representative of the entire concentration range, including stimulation of growth by low substrate concentrations. These kinetic models are tested with a variety of batch culture measurements of specific growth rate and respiration rate at widely-ranging substrate concentrations. Using one of the kinetic models, equations are developed for batch, continuous, and exponential-feed reactors. Comparison of results obtained in continuous culture with results from exponential-feed culture systems is shown to offer a novel experimental method for evaluating the effect of the cell age distribution on the properties and metabolic activity of a culture.

521 citations


Journal ArticleDOI
TL;DR: The kinetics of the batch-wise liquid phase oxidation of ferrous sulfate by the organism Thiobacillus ferrooxidans has been studied over a range of temperatures from 20°C to 31°C and in the presence of an abundant supply of oxygen, carbon dioxide, and other nutrients.
Abstract: The kinetics of the batch‐wise liquid‐phase oxidation of ferrous sulfate by the organism Thiobacillus ferrooxidans has been studied over a range of temperatures from 20°C to 31°C and in the presence of an abundant supply of oxygen, carbon dioxide, and other nutrients.

188 citations


Journal ArticleDOI
Leonard Keay1, Bernard S Wildi1
TL;DR: The B. subtilis NRRL B3411 neutral protease has been extensively purified by solvent, and salt fractional ion, pigment removal with DEAE‐cellulose followed by chromatography on hydroxylapatite, and a final passage through a Sephadex G‐100 column.
Abstract: B. subtilis NRRL B3411 neutral protease has been extensively purified by solvent, and salt fractional ion, pigment removal with DEAE‐cellulose followed by chromatography on hydroxylapatite, and a final passage through a Sephadex G‐100 column. The neutral protease was shown to be homogeneous by disc gel and cellulose acetate electrophoresis, gel filtration chromatography, and ultra‐centrifugation. The molecular weight was determined by osmometry and ultracentrifugation to be about 38–42,000 and the amino acid composition and zinc content determined. The general properties of the enzyme, pH‐activity relationship, stability, effect of inhibitors, and specificity are discussed. Comparative studies were carried out on the B. subtilis NRRL B3411 and B. subtilis var. amylosacchariticus neutral proteases and these enzymes were found to be indistinguishable by the methods used, but quite distinct from the thermostable enzyme thermolysin from B. thermoprotcolyticus.

152 citations


Journal ArticleDOI
TL;DR: It was shown that gel‐cell granules which had lost part of their 11‐β‐hydroxylase activity on storage could be reactivated yielding preparations with increased activity.
Abstract: Fungal cells from Curvularia lunata were entrapped in a crosslinked polyacrylamide gel. The gel-cells obtained as granules were applied in the microbial transformation of Reichstein compound S leading to cortisol through an 11-β-hydroxylation step. Some kinetic studies of this conversion using gel-cells were carried out. In addition, it was shown that gel-cell granules which had lost part of their 11-β-hydroxylase activity on storage could be reactivated yielding preparations with increased activity. From Corynebacterium simplex a steroid dehydrogenase catalyzing the Δ1- dehydrogenation of cortisol leading to prednisolone was isolated and partially purified. The preparation was entrapped in a crosslinked polyacrylamide gel and the gel-enzyme granules obtained used in steroid dehydrogenation processes.

152 citations



Journal ArticleDOI
TL;DR: A model system is proposed for the continuous steady state Saccharification of ground substrate in which there is continuous removal of concentrated glucose syrup, and a feedback of enzyme.
Abstract: Cellulase of Trichoderma viride was concentrated in various molecular cutoff membranes, and flux rates and retention of activity were studied under ultra‐filtration conditions. Little or no Cellulase was discharged through the membranes tested. The concentrated (5–8‐fold) enzymes were used to saccharify finely ground substrate (Solka Floe) in stirred tank (STR) and membrane reactors (MR). A pressure filtration vessel provided with a membrane for simultaneous removal of low molecular weight products (glucose) from the reacting system (Cellulose‐Cellulase) is designated as a membrane reactor. Continuous digestion of dense cellulose suspension in the membrane reactor was achieved. Using PM‐30 (Amicon) membrane reasonably high mass flux values (9.7–23.3 gals/ft2—day) were obtained in separating glucose from a digest of 30% cellulose suspension. Abcor membrane (HFA 300) was equally effective and necessitated less care in handling. Nearly 14% glucose concentration has been achieved in less than 50 hrs in STR by digesting a 30% cellulose suspension. Based on experimental data a model system is proposed for the continuous steady state Saccharification of ground substrate in which there is continuous removal of concentrated glucose syrup, and a feedback of enzyme.

116 citations


Journal ArticleDOI
TL;DR: It has been shown that lactate inhibits growth after the log phase and that the maintenance of low lactate concentrations after this point permits higher specific growth rates and higher maximum cell concentrations.
Abstract: Growth and lactic acid production by L. delbrueckii was studied in a dialysis culture system and the inhibitory effect of lactate confirmed by removing lactate from the culture medium by dialysis. It has been shown that lactate inhibits growth after the log phase and that the maintenance of low lactate concentrations after this point permits higher specific growth rates and higher maximum cell concentrations. Acid production is also significantly higher in a dialysis culture system. Finally, a modification of the Luedeking‐Piret model, incorporating the lactate inhibition effect, is proposed.

106 citations


Journal ArticleDOI
TL;DR: The microbiological extraction of zinc from a high‐grade zinc sulfide concentrate has been investigated, using a pure strain of Thiobacillus ferrooxidans, with positive effects on zinc extraction rate and in some instances on final zinc concentration in solution.
Abstract: The microbiological extraction of zinc from a high-grade zinc sulfide concentrate has been investigated, using a pure strain of Thiobacillus ferrooxidans. Conditions such as temperature, pH, pulp density, nutrient, concentration, and specific surface of solids have been studied in terms of their effects on zinc extraction rate and in some instances on final zinc concentration in solution. Where appropriate, optimum conditions for leaching have been specified.

101 citations


Journal ArticleDOI
TL;DR: Two kinds of mathematical models have been developed for batch penicillin fermentations: (1) general models, based on averaged, nondimensionalized cell andPenicillin synthesis curves from plant, scale fermentors and (2) particular models developed from specific sets of experimental data from two sources.
Abstract: Two kinds of mathematical models have been developed for batch penicillin fermentations: (1) general models, based on averaged, nondimensionalized cell and penicillin synthesis curves from plant, scale fermentors and (2) particular models developed from specific sets of experimental data from two sources. Parameter-temperature functions used with the general models were assumed to have general shapes which could apply to many fermentations, i.e., they were based on the familiar temperature response of enzyme-catalyzed reactions. Parameter-temperature functions for the particular models were determined from experimental data for batch runs at various temperatures.

96 citations


Journal ArticleDOI
TL;DR: In this article, the existence of limit cycle oscillations in a model in which predator growth rate is a function of the concentration of prey has been investigated using the singular points and phase plane portraits of early predator-prey models.
Abstract: Mathematical models of the interaction between predator and host populations have been expressed as systems of nonlinear ordinary differential equations. Solutions of such systems may be periodic or aperiodic. Periodic, oscillatory solutions may depend on the initial conditions of the system or may be limit cycles. Aperiodic solutions can, but do not necessarily, exhibit oscillatory behavior. Therefore, it is important to characterize predatory-prey models on the basis of the possible types of solutions they may possess. This characterization can be accomplished using some well-known methods of nonlinear analysis. Examination of the system singular points and inspection of phase plane portraits have proved to be useful techniques for evaluating the effect of various modifications of early predator-prey models. Of particular interest is the existence of limit cycle oscillations in a model in which predator growth rate is a function of the concentration of prey.

86 citations


Journal ArticleDOI
TL;DR: A process will be presented in which an Ultrafiltration membrane serves to separate the reaction products from the enzyme and the substrate and in this manner the enzyme may be retained and re‐used.
Abstract: In most enzymatic reactions, batch or continuous, separation of the enzyme for reuse is difficult if not impossible. A process will be presented in which an Ultrafiltration membrane serves to separate the reaction products from the enzyme and the substrate. In this manner the enzyme may be retained and re-used. Furthermore, under these conditions, the enzyme need only be present in catalytic amounts regardless of the amount of product produced. Under proper operating conditions and proper ultrafiltration membrane selection, a pure solution of α-amylase from Bacillus subtilis may be retained with no loss in enzyme activity over a test period of 30 hr after steadystate has been achieved. In the presence of substrate, the membrane support and ultrafiltration cell serve as the reaction vessel for the hydrolysis of starch. The substrate is continuously pumped into the cell under constant ultrafiltration pressure. The di-, oligo-, and polysaccharides formed from the enzyme reaction then either pass through the membrane as products or are retained. The molecular weight distribution of the products is dependent on the nominal molecular weight cut-off of the membrane, absolute ultrafiltration pressure, enzyme-to-substrate ratio, temperature, and residence time of the substrate in the reactor. In addition to the partial hydrolysis of starch by α-amylase, some preliminary findings on the complete hydrolysis of starch by glucoamylase will also be presented. In these latter studies, the substrate may be completely hydrolyzed to glucose units.

Journal ArticleDOI
TL;DR: From the examination of a number of crude enzyme mixtures or fermentation beers it appears that organisms producing Bacillopeptidase A do not produce neutral protease or amylase, while organisms produced by Bacillopes B produce aneutral protease and amyl enzyme as well.
Abstract: The alkaline proteases of B. subtilis NRRL B3411, B. pumilis, and B. licheniformis have been isolated by fractionation followed by ion exchange chromatography and their homogeneity demonstrated. General enzyme properties of the B. sublitis NRRL B3411 alkaline protease have been studied and attempts made to differentiate a group of alkaline proteases. It is clear that the alkaline proteases known as Subtilisins or Subtilopeptidases are not, exclusive to B. subtilis but are common to many Bacilli and therefore the generic name Bacillopeptidases has been proposed. It is clear too that on the basis of the effect of pH on activity, amino acid composition, esterase activity, and immunological cross-reactions the Bacillopeptidases can be divided into two groups or types: (a) Bacillopcptidase A (Subtilisin A or Subtilopeptidase A) which includes Subtilisin Carlsberg, B. licheniformis, and B. pumilis alkaline proteases; (b) Bacillopeptidase B (Subtilisin B or Subtilopeptidase B) which includes B subtilis NRRL B3411, Subtilisin Novo, Subtilisin BPN' (Nagarse), alkaline protease Daiwa Kasei, and (probably) B. subtilis var. amylosacchariticus. At present, no further differentiation is possible and whether or not the enzymes within group A or B are identical remains an open question. Methods for examination of crude enzyme mixtures or fermentation beers are described and from the examination of a number of crude enzymes and fermentation beers it appears that organisms producing Bacillopeptidase A do not produce neutral protease or amylase, while organisms producing Bacillopeptidase B produce a neutral protease and amylase as well.

Journal ArticleDOI
TL;DR: Samples of oriented DNA prepared by wet spinning have been found to be very useful for physicochemical and biochemical studies with various techniques and to yield information on such fundamental properties of DNA as its hydration, electrical conductivity, and its interaction with irradiation and mutagenic and carcinogenic substances.
Abstract: Samples of oriented DNA prepared by wet spinning have been found to be very useful for physicochemical and biochemical studies with various techniques. The results obtained yield information on such fundamental properties of DNA as its hydration, electrical conductivity, and its interaction with irradiation and mutagenic and carcinogenic substances. Against this background a detailed description is given of the wet, spinning apparatus and of the techniques developed to produce bigger samples from spun films of oriented DNA. Photographic illustrations are used to give a clear picture of the various details. Extensions of the wet spinning method are discussed.

Journal ArticleDOI
TL;DR: The present paper criticizes the use of the Monod equation as a dynamic relationship and offers as an alternative a dynamic equation relating specific growth rate to the limiting substrate concentration in the chemostat.
Abstract: A number of experimental studies on the dynamic, behavior of the chemostat have shown that the specific growth rate does not, instantaneously adjust to changes in the concentration of limiting substrate in the chemostat following disturbances in the steady state input limiting substrate concentration or in the steady state dilution rate. Instead of an instantaneous response, as would be predicted by the Monod equation, experimental studies have shown that the specific growth rate experiences a dynamic lag in responding to the changes in the concentration of limiting substrate in the culture vessel. The observed dynamic lag has been recognized by researchers in such terms as an inertial phenomenon and as a hysteresis effect, but as yet a systems engineering approach has not been applied to the observed data. The present paper criticizes the use of the Monod equation as a dynamic relationship and offers as an alternative a dynamic equation relating specific growth rate to the limiting substrate concentration in the chemostat. Following the development of equations, experimental methods of evaluating parameters are discussed. Dynamic responses of analog simulations (incorporating the newly derived equations) are compared with the dynamic responses predicted by the Monod equation and with the dynamic responses of experimental chemostats.

Journal ArticleDOI
TL;DR: Optimization methods based on the continuous maximum principle and the calculus of variations were used and indicated that an improvement, in penicillin yield of about 15% was possible if the optimum temperature profiles were followed.
Abstract: Optimization methods based on the continuous maximum principle and the calculus of variations were used to calculate optimum temperature profiles for batch penicillin fermentations. These methods were first applied to several general models to develop effective techniques for the numerical solution of the equations. Subsequently, these methods were applied to two particular models, derived from experimental data, and the optimum temperature profiles were determined. The results indicated that an improvement, in penicillin yield of about 15% was possible if the optimum temperature profiles were followed.


Journal ArticleDOI
TL;DR: Columns were used with some success for the continuous conversion of starch and Pretreatment of the starch with α‐amylase and clarification were necessary to prevent blocking of the column.
Abstract: Glucoamylase bound to DEAE‐cellulose in 0.05 M sodium acetate, pH 4.0, is active in the conversion of starch to glucose. The activity of the DEAE‐cellulose‐bound enzyme ranges from 16 to 55% of the activity of the free enzyme. Binding of the enzyme narrows the pH optimum to approximately 4.0 and lowers the temperature optimum to 40–50°C as compared to a 60°C temperature optimum for the free enzyme. Concentrations of acetate buffer above 0.1 M disrupt the DEAE‐cellulose‐enzyme complex. Columns were used with some success for the continuous conversion of starch. Pretreatment of the starch with α‐amylase and clarification were necessary to prevent blocking of the column. Columns maintained activity for more than 3 weeks of continuous operation.

Journal ArticleDOI
TL;DR: A model which has no real biochemical basis but which gives good experimental correlation has been proposed and it is shown that an ‘apparent’ lag in batch cultures will be observed if the innoculum is of very low viability.
Abstract: The effect of the rate of ‘natural death’ of bacteria on the steady state behaviour of continuous culture has been studied. A model which has no real biochemical basis but which gives good experimental correlation has been proposed. Populations of Acrobacter Acrogenes harvested from the chemostat at dilution rates greater than 0.1 HR−1 were found to be over 95% viable. The effect of the rate of death on the steady state yields becomes significant only at very low dilution rates. The experimental work of other workers has also been simulated to test the validity of the model. Theoretically it is also shown that an ‘apparent’ lag in batch cultures will be observed if the innoculum is of very low viability.

Journal ArticleDOI
TL;DR: In this article, two types of steam-sterilizable dissolvedoxygen probs were evaluated for use in fermentations and a galvanic-cell probe was selected over a polarographic probe because of its demonstrated ruggedness and dependability.
Abstract: Two types of steam‐sterilizable dissolved‐oxygen probs were evaluated for use in fermentations. A galvanic‐cell probe was selected over a polarographic probe because of its demonstrated ruggedness and dependability. Various methods for determining kLa in fermentors were compared and the oxygen balance method selected for use in viscous streptomycete fermentations. Rheological data are presented to identify a range of mash viscosity where many kLa measurement methods are not applicable. Oxygen transfer data are presented for streptomycete fermentations pilot fermentors.

Journal ArticleDOI
TL;DR: In order to isolate proteins from microalgae, yeasts and bacteria, cell disintegration in a special ball‐mill was performed and the degree of disintegration of the different microorganisms was compared.
Abstract: In order to isolate proteins from microalgae, yeasts and bacteria, cell disintegration in a special ball‐mill was performed. The degree of disintegration of the different microorganisms was compared. The dependence of disintegration on bead size and on the ratio between the volume of suspension and the volume of glass beads was also investigated. Nondisintegrated and disintegrated cells were extracted with sodium hydroxide and the amount of extractable nitrogen and the amount of nitrogen precipitable at pH 4.0 were determined. The dependence of yield on the sodium hydroxide concentration, extraction time, and temperature was studied. When extracting undisintegrated cells, very low yields were obtained and the nitrogen extracted was mostly nonproteinous. For disintegrated cells high yields were obtained. An optimum was found after extraction with 0.3–0.5% sodium hydroxide; at pH 11.0–11.5. The precipitate obtained represented 60–70% of the cell nitrogen. The nitrogen content of the precipitate was 12–14% of the dry weight.

Journal ArticleDOI
TL;DR: In this paper, the authors compared the performance of polyelectrolyte flocculating additives with traditionally available additives, and found that strong anionic and strong cationic poly electrolytes and mineral hydrocolloids were the most effective in their enhancement of settling rates.
Abstract: The removal of cellular material from fermentation broths is of importance in many fermentation processes. The present work compares the performance of recently developed polyelectrolyte flocculating additives with traditionally available additives. Objectives are to establish criteria for the choice of a flocculating additive and establish optimum conditions for the formation of stable, fast settling floe, and for quantitative separation of cellular material from the medium. Fermentation broths of actively growing Candida intermedia were used to evaluate the effectiveness of fifty commercial flocculating additives at different dosages and pH values. Certain strong anionic and strong cationic polyelectrolytes and mineral hydrocolloids were found to be most effective in their enhancement of settling rates. Some differences in behavior exist between glucose grown cells, hydrocarbon grown cells, and washed cells in buffer suspension. Flocculation of cells from fermentation broths is concluded to be highly dependent upon adsorbed material. A high charge density to interact or compete with adsorbed material and a solubility in the adsorbed material are important factors in choosing an additive for a given application. The fluid mechanics of a flocculating suspension is an important variable since low shear does not provide adequate contacting between cells for floe formation and high shear leads to floe breakup. An apparatus was constructed to grow floe under constant fluid mechanical conditions both in laminar and turbulent flow regimes. Turbulent shear was found to be very important in forming large, compact floe in cases where irreversible ionic bridging is the mechanism as for the strong anionic polyelectrolyte, polystyrene sulfonate. Adequate mixing is required to disperse the flocculating additive, but the level of turbulence is relatively unimportant in cases where reversible colloidal bridging is the mechanism as for the mineral hydrocolloid, bentonite.


Journal ArticleDOI
TL;DR: The results indicate that, the activation energy for thermal destruction of yeast was reduced from the normal heat treatment value of 84 kcal/°K mole to about 38 kcal/ °K mole.
Abstract: One important economical method for producing singlecell protein is to spray dry the cultured cells. This study presents some preliminary data on the effects of spray drying on cell viability. Under conditions similar to those for the production of spray-dried milk, 4–5 log cycles destruction occurred. The results indicate that, the activation energy for thermal destruction of yeast was reduced from the normal heat treatment value of 84 kcal/°K mole to about 38 kcal/°K mole.

Journal ArticleDOI
TL;DR: A mathematical model of the transient behavior of a product‐limited system is proposed, and analog computer solutions fitted to the experimental data are proposed.
Abstract: The stability characteristics of a continuous culture system were studied following the addition of the natural product inhibitor, ethanol. For a steady state culture of Klebsiella (Aerobacter) aerogenes there was a linear dependence of growth rate on ethanol concentration. Following impulse and step addition of the inhibitor, response patterns of the growth rate (μ) and overall metabolism (Qo2, QCo2, QAC) were observed. A mathematical model of the transient behavior of a product-limited system is proposed, and analog computer solutions fitted to the experimental data. The transient response of the growth rate could best be described by second or higher order equations, e.g., with values of the second order time constant (T2) = 5 min, and damping coefficient (ξ) = 0.4.

Journal ArticleDOI
TL;DR: The amylase of Bacillus subtilis NRRL B3411 has been purified and partially characterized and is a liquefying α‐amylase as determined by analysis of hydrolysis products and immunological studies.
Abstract: The amylase of Bacillus subtilis NRRL B3411 has been purified and partially characterized. The specific activity can be increased from 300,000 units/g to 6,000,000 units/g with a 60% recovery of total units. The purified material consists of one major and one trace anodic component as determined by disc gel electrophoresis. The molecular weight was 48,000 as determined by bio-gel filtration; the molecular weight was 44,900 ± 2400 as determined by sedimentation equilibrium methods. This purified enzyme is stable at, 70°C in the presence of 0.01 M Ca++ and 0.1 M NaCl over a broad pH range from 5.5–9.5. The pH activity profile indicates optimum activity at pH 6.0. This amylase exhibits maximum activity at 60°C. The enzyme is a liquefying α-amylase as determined by analysis of hydrolysis products and immunological studies.

Journal ArticleDOI
TL;DR: The kinetics for enzyme contained in cells are developed and the distribution of the enzyme among uninduced bacteria is presented and it was found that nearly all of the cells from balanced growing culture are immediately inducible even with doubling times as short as 7.6 hrs.
Abstract: The utilization of an exogenous substrate by enzyme inside a bacterial cell can be limited by diffusion up to the cell, penetration of the cell, diffusion within the cell, and/or attack by internal enzyme. For small molecular weight substrates such as galactosides, and for bacteria such as Escherichia coli the diffusion steps are not rate limiting even with the permeases fully induced and the external concentration of substrate low. In permeaseless organisms with more than about 20 enzyme molecules per cell, permeation of O-nitrophenyl-β-D-galactoside through the membrane is limiting. Thus, a single initiation of transcription of a lactose message suffices to yield enough enzyme molecules to switch an uninduced cell from enzyme limitation to permeability limitation. Subsequent initiations change the cellular activity very little. This transition can be followed by assaying enzyme activity of both intact and lysed cell suspensions. In this way the induction response amongst cells in growing populations at high inducer concentrations has been found to be uniform. It was found that nearly all of the cells from balanced growing culture are immediately inducible even with doubling times as short as 7.6 hrs. At 24 hrs about 1/3 of the cells are inert at any time, but all cells synthesize enzyme within a 3-hour period. At low inducer concentration or in the present of catabolite repressor the rate of initiation is greatly decreased; this leads to a non uniform distribution of enzyme within the cells, which is readily detected by the experimental technique. In addition to developing the kinetics for enzyme contained in cells, the distribution of the enzyme among uninduced bacteria is presented.

Journal ArticleDOI
TL;DR: A simple model is proposed for continuous stirred microbial culture system to explain observed deviations from the behavior predicted on the basis that the fluid is completely mixed, which arises from the use of radial flow impellers in such apparatus.
Abstract: A simple model is proposed for continuous stirred microbial culture system to explain observed deviations from the behavior predicted on the basis that the fluid is completely mixed, which arises from the use of radial flow impellers in such apparatus.

Journal ArticleDOI
TL;DR: In this article, an enzymatic system in a repeated batch process where the enzyme is subject to deactivation was studied, and pH and temperature control policies were determined that would maximize the product yield.
Abstract: This paper is concerned with the study of an enzymatic system in a repeated batch process where the enzyme is subject to deactivation. The particular system studied was the enzymatic hydrolysis of Penicillin G to 6-aminopenicillanic acid. Utilizing standard optimization techniques, pH and temperature control policies were determined that would maximize the product yield.

Journal ArticleDOI
TL;DR: The extendedculture kinetic data are shown to be substantially different from continuous culture kinetic data, and reason for these differences are discussed in light of diffrences in the cell age distributions, as well as possible differences in experimental conditions.
Abstract: Extended culture, a special type of semicontinuous culture, permits prolonged maintenance of a constant or programmed environment in a growing culture by a controlled addition of one or more substrates. Differences between extended culture and continuous culture data are a measure of differences in the properties of cell populations with different cell age distributions but identical steady-state environments. Both extended culture and continuous culture were used to study the growth kinetics of Candida utilis (ATCC 9226) under conditions of substrate inhibition at controlled concentrations of sodium acetate in a carbon-limited mineral salts medium supplemented with 0.01 g/1 yeast extract. Acetate concentrations ranged from 1.2 g/l to 10.8 g/l (expressed as acetic acid), while yeast concentrations varied from 0.3 to 7.8 (g dry cells)/1. Rate parameters such as growth yields (Y), specific growth rates (μ), and linear growth rates (K), were calculated by computer from the data and theory presented herein. Specific growth rates as high as 0.54/hr were observed, although extended culture growth was more nearly linear than exponential in these experiments. Growth yields usually varied between 0.2 and 0.4 (g dry cells)/(g acetate), although values were as high as 0.8 for a brief period during one experiment. Growth yields at a given acetate concentration were correlated by an equation of the form 1/Y = 1/YG + m/μ. A maintenance coefficient (m) of 0.17 (g acetate)/(g dry cell-hr) was observed at acetate concentrations of 4.5 and 10. g/1. A typical maximum growth yield (YG) of 0.51 (g dry cell)/(g acetate) was obtained at 4.5 g/1 acetate, but an unusually high YG of 1.33 was found at 10. g/1 acetate. Oxygen uptake measurements are compared with these cell yield measurements. Linear growth rates in expended culture were correlated by the equation K = 0.89–0.70 (S/S0) where K has units of (g dry cell)/(l-hr), S is the instantaneous acetate concentration, and S0 is the initial acetate concentration. The extended culture kinetic data are shown to be substantially different from continuous culture kinetic data. Reason for these differences are discussed in light of diffrences in the cell age distributions, as well as possible differences in experimental conditions.

Journal ArticleDOI
TL;DR: A mathematical model which can be used to describe butch growth in fermentations with two liquid phases present is developed for systems in which the growth limiting substrate is dissolved in the dispersed phase.
Abstract: In this work, a mathematical model which can be used to describe butch growth in fermentations with two liquid phases present is developed for systems in which the growth limiting substrate is dissolved in the dispersed phase. The model takes into account the drop size distribution, the rate of adsorption of cells on the drop surface, the rate of desorption of cells from the drop surface, substrate transport between phases, phase equilibrium, and growth kinetics. The model also considers the effect, of coalescence and redispersion of oil drops in the system. It is assumed that the composition of the dispersed phase is such that substrate utilization from it causes little or no change in the interfacial area. A discrete uniform distribution and a discrete normal distribution which is obtained from an experimental distribution curve are used as drop size distributions. Simulation results are obtained for a wide range of parameter values using the IBM S/360 Continuous System Modeling Program.