Glucose-limited chemostat culture of Chinese hamster ovary cells producing recombinant human interferon-gamma

A Chinese hamster ovary (CHO) cell line expressing recombinant human interferon-gamma (IFN-gamma) was grown under glucose limitation in a chemostate at a constant dilution rate of 0.015 h(-1) with glucose feed concentrations of 2.75 mM and 4.25 mM. The changes in cell concentration that accompanied changes in the glucose feed concentration indicated that the cells were glucose-limited. The cell yield on glucose remained constant, but there was a decline in residual glucose concentration and a reduced lactate yield from glucose in the latter stages of the culture. The consumption rates for many of the essential amino acids were increased later in the culture. The volumetric rate of interferon-gamma production was maintained throughout the course of this culture, indicating that IFN-gamma expression was stable under these conditions. However, the specific rate of IFN-gamma production was significantly lower at the higher glucose feed concentration. Under glucose limitation, the proportion of fully glycosylated IFN-gamma produced by these cells was less than that produced in the early stages of batch cultures. The proportion of fully glycosylated IFN-gamma increased during transient periods of glucose excess, suggesting that the culture environment influences the glycosylation of IFN-gamma.     

Metabolic and kinetic studies of hybridomas in exponentially fed-batch cultures using T-flasks

Exponentially fed-batch cultures (EFBC) of a murine hybridoma in T-flasks were explored as a simple alternative experimental tool to chemostats for the study of metabolism, growth and monoclonal antibody (MAb) production kinetics. EFBC were operated in the variable volume mode using an exponentially increasing and predetermined stepwise feeding profile of fresh complete medium. The dynamic and steady-state behaviors of the EFBC coincided with those reported for chemostats at dilution rates below the maximum growth rate. In particular, steady-state for growth rate and concentration of viable cells, glucose, and lactate was attained at different dilution rates between 0.005 and 0.05 h^–1. For such a range, the glucose and lactate metabolic quotients and the steady-state glucose concentration increased, whereas total MAb, volumetric, and specific MAb production rates decreased 65-, 6-, and 3-fold, respectively, with increasing dilution rates. The lactate from glucose yield remained relatively constant for dilution rates up to 0.03 h^–1, where it started to decrease. In contrast, viability remained above 80% at high dilution rates but rapidly decreased at dilution rates below 0.02 h^–1. No true washout occurred during operation above the maximum growth, as concluded from the constant viable cell number. However, growth rate decreased to as low as 0.01 h^–1, suggesting the requirement of a minimum cell density, and concomitant autocrine growth factors, for growth. Chemostat operation drawbacks were avoided by EFBC in T-flasks. Namely, simple and stable operation was obtained at dilution rates ranging from very low to above the maximum growth rate. Furthermore, simultaneous operation of multiple experiments in reduced size was possible, minimizing start-up time, media and equipment costs.Abbreviations EFBC exponentially-fed batch culture - CSC continuous suspended culture - MAb monoclonal antibody - D dilution rate - q _i metabolic quotient or specific rate of consumption or production of i     

Kinetics of product formation in batch and continuous culture of Clostridium barkeri

Summary The main fermentation end products in batch culture (unlimited glucose supply) of Clostridium barkeri were butyrate and lactate. The specific rate of butyrate production was linearly proportional to the growth rate while the specific rate of lactate production increased at low growth rates. In a glucose limited chemostat culture butyrate production was partly growth associated while acetate and lactate production was growth associated. Lactate was, however, only produced at high dilution rates. By varying the glucose concentration in the inflowing medium it was shown that lactate production was stimulated by a high feeding rate of the carbon source. These results are discussed in view of the fructose-1,6-diphosphate dependent lactate dehydrogenase activity in many other organisms.     

Improved production of live cells of Lactobacillus rhamnosus by continuous cultivation using glucose-yeast extract medium

In this study, the growth kinetics of Lactobacillus rhamnosus and lactic acid production in continuous culture were assessed at a range of dilution rates (0.05 h(-1) to 0.40 h(-1)) using a 2 L stirred tank fermenter with a working volume of 600 ml. Unstructured models, predicated on the Monod and Luedeking-Piret equations, were employed to simulate the growth of the bacterium, glucose consumption, and lactic acid production at different dilution rates in continuous cultures. The maximum specific growth rate of L. rhamnosus, mu-max, was estimated at 0.40 h(-1), and the Monod cell growth saturation constant, Ks, at approximately 0.25 g/L. Maximum cell viability (1.3 x 10(10) CFU/ml) was achieved in the dilution rate range of D = 0.28 h(-1) to 0.35 h(-1). Both maximum viable cell yield and productivity were achieved at D = 0.35 h(-1). The continuous cultivation of L. rhamnosus at D = 0.35 h(-1) resulted in substantial improvements in cell productivity, of 267% (viable cell count) that achieved via batch cultivation.     

Control of lactate production by Selenomonas ruminantium: homotropic activation of lactate dehydrogenase by pyruvate.

Selenomonas ruminantium produced one mole of D(-)-lactate per mole of glucose used at all dilution rates in ammonia-limited continuous culture. In contrast, lactate production varied according to the dilution rate when glucose was the limiting nutrient. At dilution rates of less than 0.2 h-1, acetate and propionate were the main fermentation products and lactate production was low. At dilution rates above 0.2 h-1, the pattern changed to one of high lactate production similar to that under ammonia limitation. Experiments with cell-free extracts of S. ruminantium showed that D(-)-lactate dehydrogenase had sigmoidal kinetics consistent with homotropic activation of the enzyme by its substrate, pyruvate. This feature allows S. ruminantium to amplify the effects of relatively small changes in the intracellular concentration of pyruvate to cause much larger changes in the rate of production of lactate. Some confirmation that this mechanism of control occurs under physiological conditions was obtained in glucose-limited culture, in which the sigmoidal increase in lactate production was accompanied by a linear increase in pyruvate excretion as the dilution rate increased.     

Effect of operating parameters on specific production rate of a cloned-gene product and performance of recombinant fermentation process

A two-stage continuous system in combination with a temperature-sensitive expression system were used as model systems to maximize the productivity of a cloned gene and minimize the problem associated with the plasmid instability for a high-expression recombinant. In order to optimize the two-stage fermentation process, the effects of such operational variables as temperature and dilution rate on productivity of cloned gene were studied using the model systems and a recombinant, Escherichia coli K12 DeltaH1 Deltatrp/pPLc23trp A1. When the expression of cloned gene is induced by raising the operating temperature above 38 degrees C, a significant decrease in the colony-forming-units (CFU) of the plasmid-harboring cell was observed, and the decrease was related to the product concentration. In order to describe this phenomenon, a new kinetic parameter related to the metabolic stress (metabolic stress factor) was introduced. It is defined as the ratio of the rate of change of pheno-type from colony-forming to non-colony-forming cells to the product accumulation per unit cell mass. At a fixed temperature of 40 degrees C, the varying dilution rate D in the range of 0.35-0.90 h(-1) did not affect the metabolic stress factor significantly. At a fixed dilution rate of D = 0.35 h(-1), this factor remained practically constant up to 41 degrees C but increased rapidly beyond 41 degrees C. The effects of temperature and dilution rate in the second stage on the specific production rate were also studied while maintaining the apparent specific growth rate (mu(2) (app)) of the second stage constant at or near mu(2) (app) = 0.26 h(-1). Under a constant dilution rate, D(2) = 0.35 h(-1), the maximum specific production rate obtained was about q(p, max) = 38 units TrpA/mg cell/h at 41 degrees C. At a constant temperature, T(2) = 40 degrees C, specific production rate increased with decreasing dilution rate with in the dilution rate range of D(2) = 0.35-0.90 h(-1). Based on the results of our study, the optimal operating conditions found were dilution rate D(2) = 0.35 h(-1) and operating temperature T(2) = 41 degrees C at the apparent specific growth rate of 0.26 h(-1). Under the optimal operating conditions, about threefold increase in productivity was achieved compared to the best batch culture result. In addition, the fermentation period could be extended for more than 100 h.     

Physiological behaviour of Hanseniaspora guilliermondii in aerobic glucose-limited continuous cultures

The physiology of Hanseniaspora guilliermondii was studied under aerobic glucose-limited conditions using the accelerostat procedure (continuous acceleration of dilution rate) and classical chemostat cultures. By both cultivation techniques this yeast was found to be Crabtree-positive. Up to a dilution rate of 0.25 h(-1), glucose was completely metabolised into biomass, glycerol and carbon dioxide. Above this value, an increase in the dilution rate was accompanied by the production of other metabolites like ethanol, acetic and malic acids. Biomass yield during the purely oxidative growth was 0.49 g g(-1) and decreased to 0.26 g g(-1) for D=0.34 h(-1). A maximal specific ethanol production rate of 1.36 mmol g(-1) h(-1) and a maximal ethanol yield of 0.05 g g(-1) were achieved at D=0.34 h(-1).     

Glucose uptake rates of single E. coli cells grown in glucose-limited chemostat cultures

To evaluate the extent to which single-cell glucose uptake rates determine the overall specific growth rate of a culture, dilute chemostat cultures of Escherichia coli BL21 were grown in defined medium under glucose limitation. The glucose uptake dynamics of the cell population was examined at the single-cell level using the fluorescent glucose analog, 2-NBDG. Between dilution rates of 0.12 h(-1) and 0.40 h(-1), mean cellular protein content and steady-state, extracellular glucose concentrations increased with increasing dilution rate. However, the distribution of 2-NBDG uptake rates in the population remained constant over the range of dilution rates studied. This indicates that the growth of cells in continuous culture is not limited by the maximum rate of uptake of glucose but by the availability of glucose for transport. The work represents an example of how quantitative flow cytometry can be applied to gain detailed insight into microbial growth physiology.     

甲醇抑制时重组毕赤酵母发酵的特性研究

本文对毕赤酵母进行了恒化培养研究。以甲醇为唯一碳源时,在稀释率较低时(D<0.048 h^-1),连续培养系统操作很稳定。但在稀释率高时(D>0.048h^-1),连续培养系统的定态点不止一个,实验不能维持,故采用比生长速率恒定的分批流加培养进行研究。结果表明,毕赤酵母的生长符合Andrew普遍化底物抑制模型。综合考虑水蛭素的生成、底物的消耗,在生产中维持甲醇浓度为限制性浓度(0.5 g/L),且维持比生长速率为0.02 h^-1时,水蛭素Hir65的比生成速率达到最大值0.2 mg/(g·h)且甲醇的比消耗速率为0.04 g/(g·h)。     

Dependence on glucose limitation of the pCO2 influences on CHO cell growth, metabolism and IgG production

The culture levels of glucose and CO(2) have been reported to independently have important influences on mammalian cell processes. In this work the combined effects of glucose limitation and CO(2) partial pressure (pCO(2)) on monoclonal antibody (IgG) producing Chinese Hamster Ovary cells were investigated in a perfusion reactor operated with controlled cell specific medium feed rate, pH and osmolality. Under high glucose conditions (14.3 +/- 0.8 mM), the apparent growth rate decreased (from 0.021 to 0.009 h(-1)) as the pCO(2) increased to approximately 220 mmHg, while the cell specific IgG productivity was almost unchanged. The lactate yield from glucose was not affected by pCO(2) up to approximately 220 mmHg and glucose was mainly converted to lactate. A feed medium modification from high (33 mM) to low (6 mM) glucose resulted in <0.1 mM glucose in the culture. As a result of apparently shifting metabolism towards the conversion of pyruvate to CO(2), both the ratio of lactate to glucose and the alanine production rate were lowered (1.51-1.14 and 17.7-0.56 nmol/10(6) cells h, respectively). Interestingly, when the pCO(2) was increased to approximately 140 mmHg, limiting glucose resulted in 1.7-fold higher growth rates, compared to high glucose conditions. However, at approximately 220 mmHg pCO(2) this beneficial effect of glucose limitation on these CHO cells was lost as the growth rate dropped dramatically to 0.008 h(-1) and the IgG productivity was lowered by 15% (P < 0.01) relative to the high glucose condition. The IgG galactosylation increased under glucose- limited compared to high-glucose conditions.     

Production of extracellular protease and glucose uptake in Bacillus clausii in steady-state and transient continuous cultures

The production of the extracellular alkaline protease Savinase (EC 3.4.21.62) and glucose uptake in a non-sporulating strain of Bacillus clausii were investigated by analysing steady-state and transients during continuous cultivations. The specific production rate was found to have an optimum at a dilution rate between 0.14 and 0.17 h(-1), whereas the yield of Savinase on glucose was found to increase with decreasing specific growth rate. A linear relationship between the ribosomal RNA content and the specific production rate was found, indicating that the translational capacity may be limiting for product formation. The dynamics of the production of Savinase were studied during step changes in the dilution rate. During a step down in the dilution rate the specific production rate decreased immediately until it reached a new steady value. During a step-up an initial cease in the production rate was observed, but when glucose stopped to accumulate the production rate was regained. The glucose uptake was further investigated when chemostat cultures growing at different dilution rates were exposed to glucose pulses. The maximal glucose uptake capacity was found to be dependent on the initial specific growth rate. Furthermore, the adaptation to high glucose concentrations was faster at high dilution rates than at low dilution rates.     

Vancomycin production in batch and continuous culture

Production of the glycopeptide antibiotic vancomycin by two Amycolatopsis orientalis strains was examined in batch shake flask culture in a semidefined medium with peptone as the nitrogen source. Different growth and production profiles were observed with the two strains; specific production (Y(p/x)) was threefold higher with strain ATCC 19795 than with strain NCIMB 12945. A defined medium with amino acids as the nitrogen source was developed by use of the Plackett-Burman statistical screening method. This technique identified certain amino acids (glycine, phenylalanine, tyrosine, and arginine) that gave significant increased specific production, whereas phosphate was identified as inhibitory for high specific vancomycin production. Experiments made with the improved medium and strain ATCC 19795 showed that vancomycin production kinetics were either growth dissociated or growth associated, depending on the amino acid concentration. In chemostat culture at a constant dilution rate (0.087 h(-1)), specific vancomycin production rate (q(vancomycin)) decreased linearly as the medium phosphate concentration was increased from 2 to 8 mM. In both phosphate and glucose limited chemostats, q(vancomycin) was a function of specific growth rate; the maximum value was observed at D = 0.087 h(-1) (52% of the maximum specific growth rate). Under phosphate limited growth conditions, q(vancomycin) was threefold higher (0.37 mg/g dry weight/h) than under glucose limitation (0.12 mg/g dry weight/h). (c) 1996 John Wiley & Sons, Inc.     

Factors affecting microbial sulfate reduction by Desulfovibrio desulfuricans in continuous culture: limiting nutrients and sulfide concentration

The effects of sulfate and nitrogen concentrations of the rate and stoichiometry of microbial sulfate reduction were investigated for Desulfovibrio desulfuricans grown on lactate and sulfate in a chemostat at pH 7.0. Maximum specific growth rates (mu(max)), half-saturation coefficients (K(sul)), and cell yield (Y(c/Lac)) of 0.344 +/- 0.007 and 0.352 +/- 0.003 h (-1), 1.8 +/- 0.3 and 1.0 +/- 0.2 mg/L, and 0.020 +/- 0.003 and 0.017 +/- 0.003 g cell/g lactate, respectively, were obtained under sulfate-limiting conditions at 35 degrees C and 43 degrees C. Maintenance energy requirements for D. desulfuricans were significant under sulfate-limiting conditions. The extent of extracellular polymeric substance (EPS) produced was related to the carbon: nitrogen ratio in the medium. EPS production rate increased with decreased nitrogen loading rate. Nitrogen starvation also resulted in decreased cell size of D. desulfuricans. The limiting C : N ratio (w/w) for D. desulfuricans was in the range of 45 : 1 to 120 : 1. Effects of sulfide on microbial sulfate reduction, cell size, and biomass production were also ivestigated at pH 7.0. Fifty percent inhibition of lactate utilization occurred at a total sulfide concentration of approximately 500 mg/L. The cell size of D. desulfuricans decreased with increasing total sulfide concentration. Sulfide inhibition of D. desulfuricans was observed to be a reversible process. (c) 1992 John Wiley & Sons, Inc.     

Morphometric evaluation of the specific growth rate of Aspergillus niger grown in agar plates at high glucose levels

Development of surface grown cultures of Aspergillus niger no. 10 was studied at two experimental levels: (a) following the time course of the biomass density (X [=] mg cm(-2)) and fitting the data by the logistic expression, which yielded a macroscopic specific growth rate expressed as mu(obs) = (dX/Xdt)[1-(X/X(max))](-1); and (b) measuring morphometric parameters like the specific elongation rate (k) of the germ tubes and their diameters (D(h)), the colony rate of radial extension (u(r)), and the mean length of distal hyphae (L(av)) to estimate the specific growth rate with the following proposed expression: mu(calc) = u(r)ln2[L(av)ln(L(av)/D(h))](-1). Increases in the initial glucose concentration (10, 40, 70, 120, 200, and 300 g L(-1)) caused reductions in the specific growth rates, the elongation kinetics of the germ tubes, and the hyphal diameter, nevertheless, u(r) and X(max) presented parabolic behavior, showing their maxima in the interval of 90 to 120 g L(-1) of glucose. The overall macroscopic effect of the tested concentrations of glucose on surface grown cultures of A. niger was to produce densely packed and slowly extending colonies, where changes in hyphal lengths and diameters were significant. There was good agreement between mu(obs) and mu(calc) values. Hence, this work validates a kinetic model based on morphometric data to estimate the specific growth rate of molds, obtained from dry weight data, using mold cultures grown in the same solid medium i.e., agar plates. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 287-294, 1997.     

Cultivation of hybridoma cells in continuous cultures: kinetics of growth and product formation

Mouse hybridoma cells were grown in suspension in continuous stirred bioreactors. Cell growth, substrate utilization, and monoclonal antibody (MAb) production were studied using serum-free medium. Steady-state data were obtained at different dilution rates, between 0.012 and 0.039 h(-1) Viability was profoundly affected by dilution rate, particularly near the lower end of the dilution-rate range investigated. MAb concentration and productivity went through a maximum with respect to dilution rate. Lactate yield on glucose declined with in creasing dilution rate. Experiments were carried out to study the effects of medium glucose concentration on cell growth, product formation, and lactate yield on glucose. Reduction of glucose concentration in the feed medium did not considerably affect cell density and MAb concentration in the culture, but lactate levels dropped sharply; lactate yield on glucose declined substantially, indicating alterations in cell metabolic path ways for energy metabolism. Optimization strategy for continuous cell culture is discussed.     

The role of oxygen limitation in the formation of poly-β-hydroxybutyrate during batch and continuous culture of Azotobacter beijerinckii

Azotobacter beijerinckii was grown in ammonia-free glucose-mineral salts media in batch culture and in chemostat cultures limited by the supply of glucose, oxygen or molecular nitrogen. In batch culture poly-beta-hydroxybutyrate was formed towards the end of exponential growth and accumulated to about 74% of the cell dry weight. In chemostat cultures little poly-beta-hydroxybutyrate accumulated in organisms that were nitrogen-limited, but when oxygen limited a much increased yield of cells per mol of glucose was observed, and the organisms contained up to 50% of their dry weight of poly-beta-hydroxybutyrate. In carbon-limited cultures (D, the dilution rate,=0.035-0.240h(-1)), the growth yield ranged from 13.1 to 19.8g/mol of glucose and the poly-beta-hydroxybutyrate content did not exceed 3.0% of the dry weight. In oxygen-limited cultures (D=0.049-0.252h(-1)) the growth yield ranged from 48.4 to 70.1g/mol of glucose and the poly-beta-hydroxybutyrate content was between 19.6 and 44.6% of dry weight. In nitrogen-limited cultures (D=0.053-0.255h(-1)) the growth yield ranged from 7.45 to 19.9g/mol of glucose and the poly-beta-hydroxybutyrate content was less than 1.5% of dry weight. The sudden imposition of oxygen limitation on a nitrogen-limited chemostat culture produced a rapid increase in poly-beta-hydroxybutyrate content and cell yield. Determinations on chemostat cultures revealed that during oxygen-limited steady states (D=0.1h(-1)) the oxygen uptake decreased to 100mul h(-1) per mg dry wt. compared with 675 for a glucose-limited culture (D=0.1h(-1)). Nitrogen-limited cultures had CO(2) production values in situ ranging from 660 to 1055mul h(-1) per mg dry wt. at growth rates of 0.053-0.234h(-1) and carbon-limited cultures exhibited a variation of CO(2) production between 185 and 1328mul h(-1) per mg dry wt. at growth rates between 0.035 and 0.240h(-1). These findings are discussed in relation to poly-beta-hydroxybutyrate formation, growth efficiency and growth yield during growth on glucose. We suggest that poly-beta-hydroxybutyrate is produced in response to oxygen limitation and represents not only a store of carbon and energy but also an electron sink into which excess of reducing power can be channelled.     

Effects of lactate concentration on hybridoma culture in lactate-controlled fed-batch operation

To investigate the effects of lactate on cell growth and antibody production, a new method of maintaining the lactate concentration constant in a fed-batch culture is described. When the pH was initially adjusted by sodium hydroxide, the specific growth rate decreased and specific death rate increased with an increase of lactate concentration. To investigate whether the inhibition was due to the lactate concentration itself or to the osmotic pressure, the effect of the osmotic pressure adjusted by sodium chloride was compared with that of sodium lactate. When the osmotic pressure was adjusted to same condition as that of sodium lactate using sodium chloride, the specific growth data showed the same degree of growth inhibition. It was thus evident that the inhibition to cell growth was mainly due to osmotic pressure while lactate production from glucose was found to be inhibited by the lactate itself compared with sodium chloride. The specific antibody production rate had a maximum value within a certain range of lactate concentration. Moreover, specific antibody production rate had a unified relationship with the kinetic parameter mu, in spite of the different causes of inhibition by lithium lactate and sodium lactate. A certain "trade-off" relationship between growth and antibody production existed at higher growth rates.     

Compiling a molecular inventory for Mycobacterium bovis BCG at two growth rates: evidence for growth rate-mediated regulation of ribosome biosynthesis and lipid metabolism

An experimental system of Mycobacterium tuberculosis growth in a carbon-limited chemostat has been established by the use of Mycobacterium bovis BCG as a model organism. For this model, carbon-limited chemostats with low concentrations of glycerol were used to simulate possible growth rates during different stages of tuberculosis. A doubling time of 23 h (D = 0.03 h(-1)) was adopted to represent cells during the acute phase of infection, whereas a lower dilution rate equivalent to a doubling time of 69 h (D = 0.01 h(-1)) was used to model mycobacterial persistence. This chemostat model allowed the specific response of the mycobacterial cell to carbon limitation at different growth rates to be elucidated. The macromolecular (RNA, DNA, carbohydrate, and lipid) and elemental (C, H, and N) compositions of the biomass were determined for steady-state cultures, revealing that carbohydrates and lipids comprised more than half of the dry mass of the BCG cell, with only a quarter of the dry weight consisting of protein and RNA. Consistent with studies of other bacteria, the specific growth rate impacts on the macromolecular content of BCG and the proportions of lipid, RNA, and protein increased significantly with the growth rate. The correlation of RNA content with the growth rate indicates that ribosome production in carbon-limited M. bovis BCG cells is subject to growth rate-dependent control. The results also clearly show that the proportion of lipids in the mycobacterial cell is very sensitive to changes in the growth rate, probably reflecting changes in the amounts of storage lipids. Finally, this study demonstrates the utility of the chemostat model of mycobacterial growth for functional genomic, physiology, and systems biology studies.     

Kinetics of hydrogen production with continuous anaerobic cultures utilizing sucrose as the limiting substrate

In this study, local sewage sludge was acclimated to establish H2-producing enrichment cultures, which were used to convert sucrose to H2 with continuously stirred anaerobic bioreactors. The steady-state behaviors of cell growth, substrate utilization, and product formation were closely monitored. Kinetic models were developed to describe and predict the experimental results from the H2-producing cultures. Operation at dilution rates (D) of 0.075-0.167 h(-1) was preferable for H2 production, resulting in a H2 concentration of nearly 0.02 mol/l. The optimal hydrogen production rate was 0.105 mol/h occurring at D=0.125 h(-1). The major volatile fatty acid produced was butyric acid (HBu), while acetic acid and propionic acid were also produced in lesser quantities. The major solvent product was ethanol, whose concentration was only 15% of that of HBu, indicating that the metabolic flow favors H2 production. The proposed model was able to interpret the trends of the experimental data. The maximum specific growth rate (mu(max)), Monod constant (Ks), and yield coefficient for cell growth (Y(x/s)) were estimated as 0.172 h(-1), 68 mg COD/l, and 0.1 g/g, respectively. The model study also suggests that product formation in the continuous hydrogen-producing cultures was essentially a linear function of biomass concentration.