Steady States Of Continuous Culture Research Articles

Improvement of glycerol production by Candida krusei in batch and continuous cultures using corn steep liquor

No fermentation parameter was affected at phosphate concentration above 0.4 g l(-1) when KH2PO4 was used as phosphate source and the glucose consumption rate was difficult to control when corn steep liquor (CSL) was adopted as the phosphate source. However, if CSL was supplemented as a source of growth factors instead of as the phosphate source, not only glucose uptake and glycerol was improved, but also fermentation became easy to control and a steady state of continuous culture was easily obtained.

Effects of methanol on expression of an anticoagulant hirudin in recombinant Hansenula polymorpha.

A series of batch, fed-batch, and continuous cultures was carried out to analyze the effects of methanol on the fermentation characteristics of recombinant Hansenula polymorpha for the production of hirudin, an anticoagulant. Hirudin expression efficiencies were greatly influenced by the methanol concentrations in continuous and fed-batch culture modes. At a steady state of continuous culture, an optimum methanol concentration of 1.7 g l(-1) was determined at a dilution rate of 0.18 h(-1) with 1.8 mg l(-1) h(-1) hirudin productivity.

Variation of stoichiometric ratios and their correlation for monitoring and control of animal cell cultures.

The stoichiometry of animal cell cultures is examined with respect to its variation and suitability for process monitoring and control. In addition to the two often used stoichiometric ratios, i.e., lactate yield from glucose (Lac/Glc) and ammonium yield from glutamine (NH4+/Gln), five other less well characterzied ones, i.e., ammonium yield from the total consumption of amino acids (NH4+/TAA), consumption of total amino acids to glutamine (TAA/Gln), essential amino acids to glutamine (EAA/Gln), glutamine to glucose (Gln/Glc), and oxygen to glucose (OUR/Glc), are also considered. A comparison of a number of cell lines including hybridoma, BHK, and CHO cells under a wide range of experimental conditions revealed that all the cell lines have similar patterns of variation of stoichiometry. In steady states of continuous culture, Lac/Glc and Gln/Glc are primarily determined by the residual glucose concentration while TAA/Gln and EAA/Gln correlate well with the residual glutamine concentration. Ammonium formation not only is a function of glutamine concentration but also is affected by the consumption of other amino acids, particularly at low residual glutamine concentrations. NH4+/TAA turned out to be a more suitable parameter to describe the ammonium formation. Large variations of all these stoichiometric ratios are found under conditions of relatively low residual concentrations of glucose and glutamine (both ca. < 0.2-0.5 mM). Above these concentrations the stoichiometric ratios are relatively constant and are independent of the cell lines. Thus, the correlations for these stoichiometric ratios may be directly used to control the nutrient concentration at low levels which are otherwise on-line difficult to determine. A stoichiometric equation is also derived for oxygen consumption. It is found that the metabolism of amino acids can significantly contribute to the consumption of oxygen. A correlation is obtained for OUR/Glc which may be used for the monitoring and control of mammalian cell cultures.

Modeling of Multiple Steady States in Mammalian Cells. A Cybernetic Approach

Mammalian cells utilize glucose and glutamine as the two key substrates. These two nutrients are complementary and substitutable in nature and, in cellular metabolism, can be oxidized completely, or be converted to excreted metabolites. The ability of cells to grow at the same rate at different physiological states gives rise to multiple steady states in continuous culture. Experimental results indicate that the steady state reached is strongly dependent on the initial condition of cultivation, or the reaction path. However, it has been elusive to develop a correlation between initial conditions and the resulting steady states. We have used a cybernetic model as the conceptual framework to explore the effect of initial conditions on the behavior of continuous cultures. The results of simulation demonstrate that a cybernetic model is capable of illustrating the effect of the history of a culture on the resulting steady state.

Application of algebraic methods to the calculation of steady states in continuous culture

For the calculation of steady states in continuous culture and the application to optimization, numerical methods for solving the related nonlinear system of equations are usually employed. Such a system may have more than one solution butnumerical algorithms find — at best — one solution per computational run depending on the starting point. There is no proof that all the solutions are actually found. To overcome these problems algebraic methods can be employed. Many biotechnological models can be transformed into a polynomial form. In contrast to nonlinear systems in general, polynomial systems are well investigated and all solutions can be calculated with given accuracy for example by using the Gröbner Bases representation. This allows even for sensitivity studies which are difficult to handle with numerical methods. The process of transforming and solving the system of equations is automated with the computer algebra system REDUCE. In this contribution the approach is presented and examples are shown.

Physiological factors affecting streptomycin production by Streptomyces griseus ATCC 12475 in batch and continuous culture

Conditions of growth are described for the production of streptomycin by Streptomyces griseus ATCC 12475 using chemically defined minimal medium and complex medium. It was found using batch cultures that early synthesis of the antibiotic occurred during growth in minimal medium but was delayed until the onset of stationary phase in complex medium. This effect was independent of whether spores or vegetative cells were used as inoculum. Stability of streptomycin biosynthesis in continuous culture was dependent on dilution rate and medium employed. Cultures were highly unstable when grown on complex medium but could be maintained in steady states in continuous culture using minimal medium when the dilution rate was increased in a stepwise manner, starting at a dilution rate of 0.02 h −1 (15% of μ max). The effect of changing dilution rate on growth, streptomycin production and the level of streptomycin phosphotransferase was examined using this technique.

Physiological factors affecting streptomycin production by Streptomyces griseus ATCC 12475 in batch and continuous culture.

Conditions of growth are described for the production of streptomycin by Streptomyces griseus ATCC 12475 using chemically defined minimal medium and complex medium. It was found using batch cultures that early synthesis of the antibiotic occurred during growth in minimal medium but was delayed until the onset of stationary phase in complex medium. This effect was independent of whether spores or vegetative cells were used as inoculum. Stability of streptomycin biosynthesis in continuous culture was dependent on dilution rate and medium employed. Cultures were highly unstable when grown on complex medium but could be maintained in steady states in continuous culture using minimal medium when the dilution rate was increased in a stepwise manner, starting at a dilution rate of 0.02 h-1 (15% of mumax). The effect of changing dilution rate on growth, streptomycin production and the level of streptomycin phosphotransferase was examined using this technique.

054 Application of algebraic methods to the calculation of steady states in continuous culture

054 Application of algebraic methods to the calculation of steady states in continuous culture

Application of Algebraic Methods to the Calculation of Steady States in Continuous Culture

For the calculation of steady states in continuous culture and the application to optimization usually numerical methods for solving the related nonlinear system of equations are employed. Such a system may have more than one solution but numerical algorithms find - at best cases - one solution per computation run depending on the starting point. There is no proof that really all the solutions are found. To overcome these problems algebraic methods can be employed. Many biotechnological models can be transformed into a polynomial form. In contrast to nonlinear systems in general polynomial systems are well investigated and all solutions can be calculated with given accuracy for example by using the Grobner Bases representation. This allows even for sensitivity studies which are difficult to handle with numerical methods. The process of transforming and solving the system of equations is automized with the computer algebra system REDUCE. In this contribution the approach is presented and examples are shown.

Effect of multistream ethanol feeding on growth and physiological characteristics of Candida utilis in a multistage tower fermenter

The effect of using a multistream feed for carbon and energy supply on the growth and physiological activity of the yeast Candida utilis in a multistage tower fermenter has been studied. Measurements were made at steady states of continuous culture for single values of dilution rate, temperature and pH in all stages of the fermenter and with the same total ethanol supplied. A comparison of the results obtained with multistream and single-stream ethanol feeds revealed that the type of ethanol feed influences the cell growth rate, rate of ethanol dissimilation, biomass yield, productivity and the cell physiology in the individual stages of the fermenter. Multistream ethanol feeding eliminates the growth inhibition due to insufficient energy production from ethanol oxidation at higher partial pressure of oxygen in the aeration gas. Using the optimal type of ethanol feed, better process parameters for SCP production are achieved.

Effect of dilution rate on growth characteristics of Candida utilis in multistage culture systems with different interstage mixing

The effect of dilution rate on important process parameters of biomass production in two multistage culture systems with different interstage mixing has been examined. Experiments were performed in a multistage tower fermenter and in a cascade of fermenters. Measurements were made at steady-state of continuous culture under constant and identical values of ethanol concentration of 50 gl −1 in the feed, temperature, OTR and pH in both culture systems used. The microorganism used was Candida utilis. Ethanol inhibition influenced cell growth rate due to the complete dissimilation of the restricted quantity of acetate to H 2O and CO 2, leading to insufficient energy generation. The value of ethanol concentration at which ethanol started to inhibit cell growth was a combined function of OTR, S R and D. The presence of the interstage mixing resulted in more efficient ethanol conversion to biomass in the whole range of dilution rates and significantly lowered the risk of washing-out at high values of both S R and D.

Elimination of ethanol inhibition of yeast growth by a multistream ethanol feed in a multistage tower fermenter

AbstractThe effect of several types of ethanol feed into a multistage tower fermenter, under conditions of oxygen supply rate limitation, on growth and physiological activity of the yeast Candida utilis was studied. The measurements were made at steady states of continuous culture for single values of dilution rate, temperature and pH in all stages of the fermenter and with a constant total sum of ethanol supplied. It was found that the type of ethanol feed significantly affects both the economic parameters associated with biomass production and the cell physiology in the individual stages of the fermenter.

Effect of PO2 on growth and physiological characteristics of Candida utilis in a multistage tower fermentor

AbstractThe effect of increasing the partial pressure of oxygen in the aeration gas on growth and physiological activity of the yeast Candida utilis in a multistage tower fermentor was studied. The measurements were made at steady states of continuous culture for single values of dilution rate, temperature, and pH in all stages of the fermentor and with one given ethanol concentration in the growth medium feed. The partial pressure of oxygen in the gas phase was changed in the range from 165 to 310 torr. The results revealed the existence of the upper critical value of the partial oxygen pressure in the gas phase. It was demonstrated that the upper critical value of PO2 influences not only the growth rate, biomass yield, and productivity but also the cell physiology resulting in changes of respiration activity and activity of alcohol and aldehyde dehydrogenases.

Growth characteristics of Candida utilis in a multistage culture system

The effect of increasing ethanol concentration in the feed on the growth and physiological activity of the yeast Candida utilis was studied. At steady-state of continuous culture with constant values of dilution rate, temperature, and pH in all fermenters in series biomass, ethanol and volatile acid concentrations, biomass yield and productivity and respiration activity were measured. In the three-stage system the maximum biomass concentration in the effluent and maximum productivity was achieved between 20 and 25 g ethanol/l in the feed. At higher concentrations, ethanol negatively affects the coupling of oxidative phosphorylation and respiratory control of cells resulting in a decrease in biomass yield and intracellular protein content. It was shown that the presence of acetate in the medium inhibits the respiration activity of yeasts growing on ethanol.

Growth characteristics of Candida utilis on volatile substrate in a multistage tower fermentor.

The influence of increasing ethanol concentration in the feed on growth and physiological activity of the yeast Candida utlis was studied. The measurements were made at steady states of continuous culture under constant values of dilution rate, temperature, and pH in all stages of the fermentor; Synthetic ethanol was used as the sole source of carbon and energy in the concentration range 10-100 g/liter. The maximum biomass concentration in the effluent and maximum productivity was achieved at 75 g ethanol/liter in the feed. In respect to ethanol losses in the outlet and biomass yield, the optimum ethanol concentration in the input of the growth medium was found to be about 50 g/liter using a four-stage system.

Mixed culture biooxidation of phenol. III. Existence of multiple steady states in continuous culture with wall growth

AbstractIt is shown that two steady states exist in certain regions of operation of a 2‐liter continuous stirred tank biological reactor. Transition was made from one steady state to another by applying shock loads of either phenol substrate which is inhibitory to the culture at high concentrations or by adding large additional amounts of concentrated organisms. The existence of the multiple steady states is ascribed to the existence of wall growth, and their position is determined by the amount of wall growth. Transient behavior of the system did not follow the predictions of the simple wall growth model but the culture appeared to undergo a lag period immediately after applying the shock load to the system. It is concluded that the stability of a continuous culture utilizing an inhibitory substrate is improved by increasing the degree of wall growth and decreasing the substrate feed concentration. It is also concluded that small scale experiments can usually not be interpreted correctly unless the effect of wall growth is taken into account.