Specific Product Formation Rate Research Articles

Significance of the surface of immobilized Saccharomyces cerevisiae cells in ethanolic fermentation

AbstractS. cerevisiae cells immobilized in alginate beads show in many cases an increase of mean single cell volume during long‐time fermentations (successive batch cycles). The biomass loading capacity of the gel beads is characterized by a maximum volume but not by a maximum number of cells occupying the gel volume. In our system this loading capacity, i.e. the maximum volume fraction of cells per volume of beads, amounted to about 0.54. As a more important result it must be stated that the specific product formation rate in the case of fermentations negligibly influenced by diffusion hindrance is related to the total surface of the viable cells but not to their total number, total volume or total dry weight.

Relation between growth rate and erythromycin production inStreptomyces erythraeus

The relation between specific growth rate and specific rate of product formation was studied in phosphate-limited chemostat cultures ofStreptomyces erythraeus. Specific rates of formation were measured for both the final product, erythromycin A, and several of its biosynthetic precursors. In all cases rates of formation increased with inereasing growth rate, indicating that antibiotic production was strongly growth-linked.

Effects of cultural conditions on the production of phenylalanine from a plasmid-harboring E. coli strain

Phenylalanine production from E. coli KA 197/pJN6 (plasmid harboring genes for aro F, phe AFBR, AmpR and TcR) was studied under varying nutritional conditions in batch and continuous cultures. In batch culture experiments where growth was deliberately interrupted by limiting concentrations of sulphate and phosphate the phenylalanine production continued from the non-growing cells. However, the depletion of phosphate resulted in an immediate cessation of phenylalanine production but thereafter a low specific rate of phenylalanine formation resumed, while the decrease in specific rate of product formation was less after sulphate depletion. In the chemostat experiments, however, phosphate limitation was the only case where the specific rate of phenylalanine formation remained constant, while at the corresponding time in sulphate and glucose limited chemostats it was declining respectively had ceased.

General characteristics of optimal feed rate profiles for various fed‐batch fermentation processes

General Characteristics of the optimal feed rate profiles have been deduced for various fed-batch fermentation processes by analyzing singular controls and singular arcs. The optimal control sequences depend on the shapes of the specific growth and product formation rates, mu andpi, and the initial conditions. For fed-batch processes described by four mass balance equations, the most general optimal control sequence consists of a period of maximum feed rate, a period of minimum feed rate (a batch period), a period of singular feed rate (variable and intermediate), and a batch period. Degenerate sequences in which one or more periods are missing can result with a particular set of initial conditions. If the fermentation time is not critical, the singular control maximizes the net yield of product and only when the time is also important, it balances a trade off between the yield of product and the specific growth rate which dictates the fermentation time. With the sequence of optimal control known, the optimal feed rate profile determination is reduced to a problem of determining switching times.

Fermentation kinetics of spent sulfite liquor by Saccharomyces cerevisiae

The growth kinetics of the yeast Saccharomyces cerevisiae and the production rate of ethanol have been studied in batch fermentation under anaerobic conditions in a 20-L fermentor. Two substrates were used in fermentation trials: a synthetic mixture of three fermentable sugars, D-glucose, D-mannose, and D-galactose, and a low-yield liquor originating from a bisulfite cooking process. The Monod model adequately described the system in relation to the specific growth rate micro(x) and the specific product formation rate micro(P). Different fermentation parameters (growth rate, substrate utilization, and product formation) were determined for the synthetic mixture and the bisulfite liquor. It was observed that the specific growth rate is much lower in spent sulfite liquor than in a synthetic medium. However, the specific product formation rate remains the same in both media.

Utilization of spline functions for smoothing fermentation data and for estimation of specific rates

A response surface method of smoothing fermentation data with spline functions is presented. The available electron balance is used to optimally select the values of the smoothing parameters associated with the spline functions. The method is applied to six sets of anaerobic fermentation data in which pure and mixed cultures are grown in batch followed by fed batch culture. Lactobacillus bulgaricus and Streptococcus thermophilus are cultured on 3% dry milk. Measured concentrations of biomass, lactose, galactose, lactic acid, and other acid products are smoothed using spline functions. Values of specific growth rate, specific lactose consumption rate, specific galactose formation rate, and specific acid product formation rate are estimated and the consistency of the results is examined using the available electron balance. The results show that the method works reasonably well, but that an upper bound should be used for the smoothing parameters to obtain accurate estimates of the derivative quantities.

Model aided dynamic process analysis and optimization for the nourseothricin fermentation.

The relation between product formation and growth kinetics could be characterized by two facts: the specific product formation rate depends on the ageing of the population and on the specific growth rate. These relation was formulated and quantified by a mathematical model, which was fitted to experimental data of a representative fermentation run und used to predict an optimal fermentation mode. In the result of this discussion cyclic fed batch fermentation was found to be optimal.

Development of the agar‐disc method for the rapid screening of strains with increased productivity

AbstractA simple model of colony growth and product accumulation in an agar disc was developed assuming constant rate of increase of colony biomass and a maturation‐ decay behaviour of the specific productivity of the biomass. Experimental data obtained with three erythromycin‐producing strains of Streptomyces erythreus followed the predicted behaviour of the apparent specific productivity of the colony. The latter parameter exhibited a good correlation with the specific rate of product formation observed in liquid culture. A more sensitive correlation, and higher specific productivities, were obtained with agar discs made of a fermentation‐type medium than with a maintenance‐type medium. Estimation of the colony biomass through its surface area proved to be satisfactory in the conditions adopted, though it represents a major potential source of error.

Automated fermentation equipment I. program‐controlled fermentor

AbstractA fermentation system with a plug scheme unit has been developed, offering a variety of solutions to measurement, control, and operational problems. By means of the program unit, e.g., automatic pH control assigned to the dynamic of batch cultures and the feed of different ingredients controlled by a time program or a given variable have been solved. The continuous culture volume was controlled by a level controlled by a level controller equipped with a photosensor. A method was developed for variable control that provide information on the activity of the culture, and allows direct measurement of the different rate values, e.g., generation time or specific product formation rate. Applicability of the direct measurement of generation time is presented in the qualification of molasses and in a static off‐line optimization process.

Rapid ethanol fermentation of cellulose hydrolysate. II. Product and substrate inhibition and optimization of fermentor design

AbstractHigh concentrations of both ethanol and sugar in the fermentation broth inhibit the growth of yeast cells and the rate of product formation. Inhibitory effects of ethanol on the yeast strain Saccharomyces cerevisiae NRRL‐Y‐132 were studied in batch and continuous chemostat cultures. Growth was limited by either glucose or ethanol. Feed medium was supplemented with different ethanol concentrations. Ethanol was found to inhibit growth and the activity of yeast to produce ethanol in a noncompetitive manner. A linear kinetic pattern for growth and product formation was observed according to μ = μm (1 – P/Pm) and v = vm (1 – P/Pm′), where μm is the maximum specific growth rate at P = 0 (hr−1); Pm is the maximum specific product formation rate at P = 0 (hr−1); Pm is the maximum ethanol concentration above which cells do not grow (g/liter); Pm′ is the maximum ethanol concentration above which cells do not produce ethanol (g/liter). Substrate inhibition studies were carried out using short‐time experimental techniques under aerobic and anaerobic condition. The degree of substrate inhibition was found to be higher than that has been reported for ethanol fermentation of pure sugar. The kinetic relationships thus obtained were used to compute growth, substrate utilization, and alcohol production patterns and have been discussed with reference to batch and continuous fermentation of enzymatically produced bagasse hydrolysate.

Specific rates of substrate oxidation and product formation in autotrophically growingChromatium vinosum cultures

Kinetics ofChromatium metabolism under autotrophic conditions were studied in batch culture. Description of various over-all metabolic rates in equal dimensions enabled direct comparison of such different processes as electron donor oxidation, storage-polymer synthesis, and growth. In the presence of sulfide, the specific rate of sulfur oxidation is partly depressed. Upon sulfide depletion, the latter rate showed an instantaneous increase of 22%. Simultaneously, glycogen was degraded. These two modifications fully compensate for the absence of sulfide, thus enabling growth to continue withμmax (0.12 h-1). These findings indicate that the potential rate of supply of electrons exceeds the biosynthetic demand for reducing power. The synthesis of glycogen in the presence of sulfide may be regarded overflow metabolism, assuming theμmax is intrinsically limited at 0.12 h-1. An alternative hypothesis is based on the assumption of an ineffective glycogen-synthesis regulation. Conceivably, growth and glycogen synthesis are competing for biosynthetic intermediates, the supply of which is limited by the maximum specific rate of e.g. the Calvin cycle. If so, both growth and glycogen synthesis are performed at submaximal rates. The rate of glycogen synthesis is greatly enhanced by the addition of growth inhibitors, and an increasedμmax value is found in the presence of acetate. These two findings together are consistent with the second hypothesis.

Estimation of productivities in repeated fed batch cephalosporn fermentation

The theory of fed batch culture was tested on the cephalosporin C fermentation. In repeated fed batch culture a constant fraction of the culture volume is removed at fixed intervals. Since the productivity (output rate/unit volume) and specific rate of product formation may vary throughout the fed batch cycle, an “average productivity” and “average specific rate of product formation” which describe the overall behaviour of the system over several cycles are introduced. The test shows that the quasi-steady state of cephalosporin production predicted by fed batch theory can be maintained during at least 3.6 culture volume changes. The fed batch method of culture increased the productivity of the culture about 1.3 times with respect to that of simple batch culture whilst the cephalosporin C concentration was about the same in each type of culture.

Estimation of productivities in repeated fed batch cephalosporn fermentation

AbstractThe theory of fed batch culture was tested on the cephalosporin C fermentation. In repeated fed batch culture a constant fraction of the culture volume is removed at fixed intervals. Since the productivity (output rate/unit volume) and specific rate of product formation may vary throughout the fed batch cycle, an “average productivity” and “average specific rate of product formation” which describe the overall behaviour of the system over several cycles are introduced. The test shows that the quasi‐steady state of cephalosporin production predicted by fed batch theory can be maintained during at least 3.6 culture volume changes. The fed batch method of culture increased the productivity of the culture about 1.3 times with respect to that of simple batch culture whilst the cephalosporin C concentration was about the same in each type of culture.

A model for the bio-oxidation process based on product formation concepts

Data from the literature suggests that the concentration of organic matter in the effluent from a biological reactor is influenced by the concentration in the influent. Based upon the fact that the majority of the soluble organic matter in the effluent is not the original substrate, the hypothesis is put forth that most of it is microbial in origin, and therefore consists of the products of microbiol metabolism. Using the concept that the activated sludge process is a producer of organic compounds, as well as a user of them, a model is then developed which relates the effluent COD to product formation. Previously published data is then used to establish that the specific rate of product formation is related to the specific growth rate by at least a 2nd order polynomial function. The function is given and its implication to plant design and operation are discussed.

A method for the determination of confidence limits for the P/2e- ratio for chosen values of ymaxatp form the results of continuous culture experiments.

A model is described, which allows the determination of 95% confidence limits for the maintenance coefficient and the efficiency of oxidative phosphorylation for chosen values of the growth yield for ATP corrected for energy maintenace (YmaxATP). As experimental data the specific rates of substrate consumption, product formation and oxygen uptake in chemostat cultures at various growth rates are use.

Kinetics of the xanthan fermentation

AbstractXanthan gum, a heteropolysaccharide with unusual and useful properties, is now produced commercially by fermentation with Xanthomonas compestris NRRL B–1459 in a medium containing glucose, minerals, and a complex nitrogen source—distillers' dried solubles (DDS). Understanding the kinetics of the fermentation should contribute to process improvements and increase the market potential for the gum. Earlier studies showed that although DDS determined initial growth rate, growth was stopped by some mechanism other than substrate exhaustion, probably an effect related to product formation.Product formation did not require active growth, but its rate increased with cell concentration. Specific product formation rate declined at high viscosities. Varying glucose concentration from 0.5 to 5.0% and dissolved O2 tension between 20 and 90% air saturated had no effect on the rates, but pH had to be maintained near 7 and temperature near 28°C to permit continued product formation. Xanthan yield could be explained by the energy required for growth and polymerization, that energy coming from dissimilation of the part of the carbohydrate substrate not converted to polymer.

Dialysis fermentation. II. Kinetic analysis of salicylic acid production via cell growth and maintenance

AbstractA kinetic analysis was made of the relationship between salicylate production from naphthalene and growth of Pseudomonas fluorescens in semicontinuous dialysis culture. The specific rates both of product formation and growth initially were increased by the diffusional withdrawal of salicylate, but subsequently were reduced to low levels despite continued salicylate removal. Productivity and growth were correlated by the Luedeking‐Piret equation in an initial nondialysis period and in the early stages of dialysis fermentation, when specific growth rates exceeded. 005 hr−1. Below this level of growth at later stages of dialysis fermentation, the specific production rate was correlated only with total cell mass by a proportionality constant of .035 hr−1, which was attributed to maintenance metabolism. Maintenance accounted for about 84% of the total salicylate produced, while growth‐associated metabolism accounted for the remainder.