Long term shear effects on a hybridoma cell line by dynamic perfusion devices

The long term shear effects on a hybridoma cell line were studied by the simulation of a hollow fiber perfusion system. Various mechanical/environmental stress conditions were applied and steady state concentrations of live, dead and lysed cells were measured or calculated in a continuous culture. From mathematical modeling, it is shown that inclusion of a lysed cell index (LCI) renders a better fit to the material balance equation at steady state. The specific cell death rate increased with increasing shear force as expected only when the LCI was included. Without the inclusion of the LCI, the calculated specific cell growth rates are about 25–60% of the value when included. The results reported may lend some insight to design improvements since most perfusion devices add shear stresses to the cells in the reactor.List of Symbols b ml/hr continuous culture flow rate - D hr^–1 dilution rate (b/V) - m g glucose/10⁹ cells/hr specific maintenance coefficient - S ₀ g/l feed substrate concentration - S g/l reactor substrate concentration - t hr time - V ml reactor volume - X ⁺ cells/ml live cell concentration - X ^– cells/ml dead cell concentration - X ⁰ cells/ml lysed cell concentration - Y _x/s 10⁹ cells/g glucose cell/substrate yield coefficient - hr^–1 specific growth rate - hr^–1 specific death rate - hr^–1 specific lysis rate - hr^–1 specific lysis rate for simultaneous death and lysis     

Control of carbon mineralization to CH4 and CO2 in anaerobic,Sphagnum-derived peat from Big Run Bog,West Virginia

The mineralization of organic carbon to CH₄ and CO₂ inSphagnum-derived peat from Big Run Bog, West Virginia, was measured at 4 times in the year (February, May, September, and November) using anaerobic, peat-slurry incubations. Rates of both CH₄ production and CO₂ production changed seasonally in surface peat (0–25 cm depth), but were the same on each collection date in deep peat (30–45 cm depth). Methane production in surface peat ranged from 0.2 to 18.8 mol mol(C)^–1 hr^–1 (or 0.07 to 10.4 g(CH₄) g^–1 hr^–1) between the February and September collections, respectively, and was approximately 1 mol mol(C)^–1 hr^–1 in deep peat. Carbon dioxide production in surface peat ranged from 3.2 to 20 mol mol(C)^–1 hr^–1 (or 4.8 to 30.3 g(CO₂) g^–1 hr^–1) between the February and September collections, respectively, and was about 4 mol mol(C)^–1 hr^–1 in deep peat. In surface peat, temperature the master variable controlling the seasonal pattern in CO₂ production, but the rate of CH₄ production still had the lowest values in the February collection even when the peat was incubated at 19°C. The addition of glucose, acetate, and H₂ to the peat-slurry did not stimulate CH₄ production in surface peat, indicating that CH₄ production in the winter was limited by factors other than glucose degradation products. The low rate of carbon mineralization in deep peat was due, in part, to poor chemical quality of the peat, because adding glucose and hydrogen directly stimulated CH₄ production, and CO₂ production to a lesser extent. Acetate was utilized in the peat by methanogens, but became a toxin at low pH values. The addition of SO₄ ^2– to the peat-slurry inhibited CH4 production in surface peat, as expected, but surprisingly increased carbon mineralization through CH4 production in deep peat. Carbon mineralization under anaerobic conditions is of sufficient magnitude to have a major influence on peat accumulation and helps to explain the thin (< 2 m deep), old (> 13,000 yr) peat deposit found in Big Run Bog.     

Hybridoma antibody content and production rate in continuous culture: Effect of dilution rate

Summary Hybridoma IND1 viability was 95% for dilution rates (D) ranging from 45 to 100% of _max (0.037 hr^–1). Over this range, the cell concentration and total protein content increased with D. Washout occurred at D=0.041 hr^–1, but the intracellular protein content continued to increase. The high- and low-content modes of the intracellular antibody distribution did not vary with D. The fraction of cells with high antibody content decreased with time, except for an increase at D=0.041 hr^–1. This decrease did not affect the specific antibody production rate, which, like the high- and low-content modes, was independent of D.     

Anchorage-dependent animal cell culture by using a porous microcarrier

CHO-K1 cells were cultured by using a porous microcarrier. The effects of microcarrier concentration and agitation rate on cell growth in porous microcarrier cultures were investigated. The specific growth rate of 0.041 h^–1 in porous microcarrier cultures was independent of both microcarrier concentration and agitation rate. By estimating the total surface area occupied by cells from the maximum cell number, it was found that not all the surface area of the porous microcarrier was utilizable for cell growth.The maximum cell number decreased with increasing the microcarrier concentration and the agitation rate. From this result, it was also found that not all the cells grown on the interior surface of the porous microcarrier were protected against mechanical damage due to agitation. The protection capacity of the porous microcarrier was estimated to be 300 cells/carrier. The direct gas sparging into the culture broth in porous microcarrier cultures improved the cell density without mechanical damage to animal cells.List of Symbols d m microcarrier diameter - d _i m impeller diameter - d _p m mean pore diameter - n _i s^–1 agitation rate - p Pa pressure difference - v m/s velocity of microcarrier - v _p m/s average velocity flowing through cyclinder - Pa · s viscosity of medium - angle measured from stagnant point - Pa average shear stress - Pa shear stress distribution     

Observations consistent with autocrine stimulation of hybridoma cell growth and implications for large-scale antibody production

Existence of autocrine growth factors (aGFs) may influence the serum requirement for growth of hybridoma cells and thus significantly influence process economics. For the murine hybridoma cell line S3H5/2bA2, critical inoculum density (cID) and serum requirement for growth were inversely related for cultivation in both T flasks and spinner flasks. In spinner flasks, an inoculum density of 10⁶ cells/ml was necessary for the cells to grow in RPMI 1640 medium without serum supplement, and an inoculum density of 10³ cell/ml was necessary in RPMI 1640 medium with 10% serum. In T flasks, where the local cell density is higher than in spinner flasks, an inoculum density of 10⁶ cells/ml was necessary for the cells to grow in RPMI 1640 medium without serum supplement, and an inoculum density of 1 cell/ml was also necessary in RPMI 1640 medium with 10% serum. Further, immobilized cells at high local cell density could grow under conditions where cells in T flasks at corresponding overall cell density could not grow. The cells at high inoculum density were less sensitive to shear induced by mechanical agitation than the cells at low inoculum density. Taken together these observations support the existence of secreted aGF(s) by the hybridoma cell line used. Since the specific MAb production rate was independent of cultivation method and inoculum density, the existence of autocrine growth factors would suggest that the use of immobilized cells should improve the economics of MAb production.     

Feasibility study on the use of hyperosmolar medium for improved antibody production of hybridoma cells in a long-term,repeated-fed batch culture

To test the feasibility of using hyperosmolar medium for improved antibody production in a long-term, repeated fed-batch culture, the influence of various culture conditions (serum concentration and cultivation method) on the hybridoma cells' response to hyperosmotic stress resulting from sodium chloride addition was first investigated in a batch culture. The degree of cell growth depression resulting from hyperosmotic stress was dependent on serum concentrations and cultivation methods (static and agitated cultures). Depression of cell growth was most significant in agitated cultures with low serum concentration. However, regardless of serum concentrations and cultivation methods used, the hyperosmotic stress significantly increased specific antibody productivity (q _MAb). Increasing osmolality from 284 to 396 mOsm kg^–1 enhanced the q_MAb in agitated cultures with 1% serum by approximately 124% while the similar osmotic stress enhanced the q _MAb in static cultures with 10% serum by approximately 153%. Next, to determine whether this enhanced q_MAb resulting from hyperosmotic stress can be maintained after adaptation, long-term, repeated-fed batch cultures with hyperosmolar media were carried out. The cells appeared to adapt to hyperosmotic stress. When a hyperosmolar medium (10% serum, 403 mOsmkg^–1) was used, the specific growth rate improved gradually for the first four batches and thereafter, remained constant at 0.040±0.003 (average ± standard deviation) hr^–1 which is close to the value obtained from a standard medium (10% serum, 284 mOsmkg^–1) in the batch culture. While the cells were adpating to hyperosmotic stress, the q_MAb was gradually decreased from 0.388×10^–6 to 0.265×10^–6 g cell hr^–1 and thereafter, remained almost constant at 0.272±0.014× 10^–6 g cell^–1 hr^–1. However, this reduced q _MAb after adaptation is still approximately 98% higher than the q_MAb obtained from a standard medium in the batch culture.The authors would like to thank Dr.M. Kaminski for providing the hybridoma cell line used in this study. This work was supported by the Korea Science and Engineering Foundation.     

Estimation of in situ rates of heterotrophy using diurnal changes in dissolved organic matter and growth rates of picoplankton in diffusion culture

A scheme has been developed for observing diurnal changes in dissolved organic matter in the photic zone and correlating the with specific microbial fractions and their rates of growth and uptake. Particulate ATP for procaryote and protist size fractions were augmented by pigment analyses to differentiate phototroph from phagotroph dominated accumulations. A temporary daytime increase in carbohydrates of some 32% above pre-dawn threshold values accounted for 41% of the labile DOC. Polysaccharide and monosaccharide maxima were mainly associated with phagotrophic protists, the monosaccharide maxima occurring during the daytime. Apparent maximum in situ heterotrophic uptake rates of this released DOC of 9.8 g C L^–1 hr^–1 agree well with the growth rates of natural populations of the bacterial size fraction (picoplankton) on in situ water in diffusion culture of 5.1 g C L^–1 hr^–1. This growth was associated with phototroph maxima but occurred only during the afternoon and evening hours and not during the early morning and intense daylight hours. Proposed follow-up studies are outlined.     

The sodium balance of the euryhaline marine loggerhead turtle,Caretta caretta

Summary The efflux of sodium ions from the loggerhead turtle,Caretta caretta, was investigated when animals were acclimated to seawater, freshwater, and during the acclimation period after transfer from seawater to freshwater. The rate of sodium loss in animals acclimated to seawater was found to be 3 M Na · g^–1 · hr^–1. Cannulation of the cloaca showed that only 5% of the gross efflux of sodium was via the cloaca and it was calculated that 60% of the gross efflux was via nasal gland secretion and 35 % via integumentary diffusional loss. Cannulation experiments indicated that a significant amount of sodium may enter the body via the cloaca. Transfer of animals from seawater to freshwater resulted in a decline of sodium efflux by 90–99 % within 6 hr, and a further decline to only approximately 0 01 M Na · g^–1· hr^–1 after 1–2 days in freshwater. Cannulation experiments of individuals acclimated to freshwater indicated that the role of the cloaca in sodium loss in freshwater was minimal. It was calculated that sodium loss in freshwater is so small that survival in freshwater for at least 20 days is possible without active extraction of sodium from the medium. No evidence could be found for active uptake of sodium ions from freshwater baths byCaretta.This research was supported by NSF grant GB 16839.     

Improvement of the culture stability of non-anchorage-dependent animal cells grown in serum-free media through immobilization

A murine hybridoma cell line producing a monoclonal antibody against penicillin-G-amidase and a murine transfectoma cell line secreting a monovalent chimeric human/mouse Fab-antibody fragment were cultivated in three different media (serum-containing, low protein serum-free, and iron-rich protein-free) in flask cultures, stirred reactors and a fixed bed reactor. In static batch cultures in flasks both cell lines showed similar good growth in all three media.In suspension in a stirred reactor, the hybridoma cell line could be cultivated satisfactory only in serum-containing medium. In low protein serum-free medium, Pluronic F68 had to be added to protect the hybridoma cells against shear stress. But even with this supplement only batch, not chemostat mode was possible. In iron-rich protein-free medium the hybridoma cells grew also in continuous chemostat mode, but the stability of the culture was low. The transfectoma cell line did not grow in stirred reactors in any of the three media.Good results with both cell lines were obtained in fixed bed experiments, where the cells were immobilized in macroporous Siran^®-carriers. The media, which were optimized in flask cultures, could be used without any further adaptation in the fixed bed reactor. Immobilization improved the stability and reliability of cultures of non-adherent animal cells in serum-free media tremendously compared to suspension cultures in stirred reactors. The volume-specific glucose uptake rate, an, indicator of the activity of the immobilized cells, was similar in all three media. Deviations in the metabolism of immobilized and suspended cells seem to be mainly due to low oxygen concentrations within the macroporous carriers, where the cells are supplied with oxygen only by diffusion.List of symbols c substrate or product concentration mmol l^–1 - c₀ substrate or product concentration in the feed mmol l^–1 - c_Glc glucose concentration mmol l^–1 - c_Gln glutamine concentration mmol l^–1 - c_Amm ammonia concentration mmol l^–1 - c_Lac lactate concentration mmol l^–1 - c_FAB concentration of Fab# 10 antibody fragment g l^–1 - c_MAb monoclonal antibody concentration mg l^–1 - D dilution rate d^–1 - q cell-specific substrate uptake or metabolite production rate mmol cell^–1 h^–1 - q_Glc cell-specific glucose uptake rate mmol cell^–1 h^–1 - q_Gln cell-specific glutamine uptake rate mmol cell^–1 h^–1 - q_MAb cell-specific MAb production rate mg cell^–1 h^–1 - q^* volume-specific substrate uptake or metabolite production rate mmol l^–1 h^–1 - q^*FB volume-specific substrate uptake or metabolite production rate related to the fixed bed volume mmol l_FB ^–1 h^–1 - q^*FB,Glc volume-specific glucose uptake rate related to the fixed bed volume mmol l_FB ^–1 h^–1 - q^*FB,Gln volume-specific glutamine uptake rate related to the fixed volume mmol l_FB ^–1 h^–1 - q^*FB,MAb volume-specific MAb production rate related to the fixed volume mg l_FB ^–1 h^–1 - q^*FB,02 volume-specific oxygen uptake rate related to the fixed bed volume mmol l_FB ^–1 h^–1 - t time h - U superficial flow velocity mm s^–1 - V medium volume in the conditioning vessel of the fixed bed reactor l - V_FB volume of the fixed bed l - x_v viable cell concentration cells ml^–1 - y_Amm,Gln yield of Ammonia from glutamine - y_Lac,Glc yield of lactate from glucose - specific growth rate h^–1 - _d specific death rate h^–1     

A continuous culture study of an obligately psychrophilic Pseudomonas species

Summary The optimum temperatures for growth and respiration of an obligately psychrophilic Pseudomonas spec. were 14°C and 23°C, respectively. The maximum temperature for growth was between 19 and 20°C. When cells were grown in a chemostat with lactate as the growth-limiting substrate at a specific growth rate of 0.05 hr^-1 over a temperature range of 5–19°C, it was found that RNA concentration was lowest at 14°C. At lower temperatures the cells compensated the decrease of reaction rates by increasing the concentration of RNA and of respiratory enzymes. A temperature raise above 14°C also increased cellular RNA, which probably counteracted an impairment of protein synthesis. Above 18°C the RNA increase ceased, resulting in a rapid decrease of protein synthesis, until between 19 and 20°C growth ceased entirely. Cells grown at 14°C showed a linear increase of RNA content and values with growth rate, when this was varied from 0.025 to the maximum value of 0.2 hr^-1.Dedicated to Prof. C. B. van Niel on the occasion of his 70th birthday.     

n-3 PUFA productivity in chemostat cultures of microalgae

Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid productivities from chemostat cultures of an isolate of Isochrysis galbana have been studied. The productivities reached in the interval of dilution rates between 0.0295 h^–1 and 0.0355 h^–1 were 1.5mg·1^–1·h^–1 for lipids, 300 g·1^–1·h^–1 for EPA and 130g1·1^–1·h^–1 for DHA. Furthermore, light attenuation by mutual shading, and agitation speed influences on growth and fatty acid composition were analysed. A model relating steady-state dilution rates to internal average light intensity has been proposed, the parameter values of which obtained by non-linear regression were: maximum specific growth rate (_max)=0.0426 h^–1; the affinity of cells to light (I_k) = 10.92 W·m^–2; the exponent (n) = 5.13; regression coefficient (r ²)=0.9999. Correspondence to: E. Molina Grima     

An adaptive on-line control feed rate system in a laboratory scale bakers yeast process

Summary A new control policy for the on-line optimization of the nutrient supply in bakers yeast process is proposed. A feed rate corresponding to minimal substrate uptake time was shown to be optimal for cell yield and specific growth rate. Cultivation results of baker's yeast are presented.Nomenclature c glucose concentration in wort (mol.l^–1) - C total glucose used (mol) - c_e ethanol concentration in wort (mg.l^–1) - c_p glucose concentration in fresh medium (mol.l^–1) - dt/dc glucose consumption time (sec.mol^–1) - F substrate feed rate (litre.hr^–1) - q_c glucose uptake rate (mol.hr^–1) - Q_c specific glucose uptake rate (moll.g^–1.hr^–1) - qO₂ oxygen uptake rate (mol.hr^–1) - QO₂ specific oxygen uptake rate (mol.g^–1.hr^–1) - r_x productivity (g.l^–1.hr^–1) - t time (hr) - x biomass concentration (g.l^–1) - X total biomass (g) - Y_x/c cell yield (g.g^–1): (g.mol^–1) - Y_o/c consumed oxygen to glucose ratio (mol.mol^–1)     

Organic reduction of tapioca wastewaters using modified RBC

A modified Rotating Biological Contactor (RBC) was used for the treatability studies of synthetic tapioca wastewaters. The RBC used was a four stage laboratory model and the discs were modified by attaching porous nechlon sheets to enhance biofilm area. Synthetic tapioca wastewaters were prepared with influent concentrations from 927 to 3600 mg/l of COD. Three hydraulic loads were used in the range of 0.03 to 0.09 m³·m^–2·d^–1 and the organic loads used were in the range of 28 to 306 g COD· m^–2·d^–1. The percentage COD removal were in the range from 97.4 to 68. RBC was operated at a rotating speed of 18 rpm which was found to be the optimal rotating speed. Biokinetic coefficients based on Kornegay and Hudson models were obtained using linear analysis. Also, a mathematical model was proposed using regression analysis.List of Symbols A m² total surface area of discs - d m active depth of microbial film onany rotating disc - K _s mg ·l^–1 saturation constant - P mg·m^–2·^–1 area capacity - Q l·d^–1 hydraulic flow rate - q m³·m^–2·d^–1 hydraulic loading rate - S ₀ mg·l^–1 influent substrate concentration - S _e mg·l^–1 effluent substrate concentration - w rpm rotational speed - V m³ volume of the reactor - X _f mg·l^–1 active biomass per unit volume ofattached growth - X _s mg·l^–1 active biomass per unit volume ofsuspended growth - X mg·l^–1 active biomass per unit volume - Y _s yield coefficient for attachedgrowth - Y _A yield coefficient for suspendedgrowth - Y yield coefficient, mass of biomass/mass of substrate removed Greek Symbols hr mean hydraulic detention time - (_max)_A d^–1 maximum specific growth rate forattached growth - (_max)_s d^–1 maximum specific growth rate forsuspended growth - _max d^–1 maximum specific growth rate - d^–1 specific growth rate - _v mg·l^–1·hr^–1 maximum volumetric substrateutilization rate coefficient     

Growth kinetics of Thermus thermophilus

Summary The nonsporulating extreme thermophile Thermus thermophilus was grown in continuous culture at dilution rates up to 2.65 h^–1 at 75°C and pH 6.9 on complex medium. Concomitantly very low yield (Y=0.12 g cell dry weight g^–1 utilized organic carbon) and incomplete substrate utilization (always less than 45%) were found. In batch cultures T. thermophilus could be grown with _max =h^–1, in shake flasks only with _max =h^–1 with the same low yield and incomplete substrate utilization. Stable steady states at 84C and 45°C were realized at a dilution rate of 0.3 h^–1 whereas at 86°C and 40°C no growth could be detected. Artefacts arising from wall growth (in bioreactors) or improper materials must be ruled out. Inhibition of growth by organic substrates was demonstrated at low concentrations: a decrease in the yield obtained was found when more than 0.7 gl^–1 of meat extract were supplied in the medium. The maintenance requirement for oxygen is potentially very high and was determined to be 10 to 15 mmol g^–1 h^–1.     

Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation

Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (P _max) was 4.41 mol photon m^–2 s^–1 at 26 °C and 4.07 mol photon m^–2 s^–1 at 28 °C. Saturating irradiance occurred at 95 mol photon m^–2 s^–1 at 26 °C and 65 mol photon m^–2 s^–1 at 28 °C. In contrast, growth experiments at 41.7 mol photon m^–2 s^–1 caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day^–1 at 28 °C and 25 mol photon m^–2 s^–1. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation.     

Enzyme formation by a yeast cell wall lytic Arthrobacter species: chitinolytic activity

The kinetics of the release of chitinolytic activity (endochitinase EC 3.2.1.14, \-N-acetyglucosaminidase EC 3.2.1.30) by a yeast cell wall lytic Arthrobacter species was studied. The organism was cultivated on yeast cell wall, mycelium of Trichoderma reesei, colloidal chitin, N-acetylglucosamine, glucosamine and mixtures with acetate. With the exception of yeast cell wall, these substrates were used as the sole source of carbon and nitrogen. The growth on colloidal chitin (0.5%) proceeded at a maximum specific growth rate (_umax) of 0.23 h^–1 and yielded 2700 mU1^–1 chitinase. Yeast cell wall and mycelium of T. reesei supported more rapid growth (_max = 0.30 h^–1 and 0.25 h^–1 respectively) but yielded reduced chitinase activity (565 mUl^–1 and 700 mUl^–1). The growth rate on glucosamine (_max = 0.24 h^–1) was reduced when this was mixed with acetate (_max = 0.12 h^–1), whereas the enzyme yield was increased from 720 mUl^–1 to 960 mUl^–1. The same effect on growth rate was observed with glucose and equimolar mixtures of glucose and acetate, indicating a strong impact of the organic acid on carbohydrate transport or metabolism. The growth of adapted cells on N-acetylglucosamine was comparable to that observed on an equimolar mixture of glucosamine and acetate, indicating that N-acetylglucosamine is rapidly hydrolysed by adapted cells.     

Optimization of recombinantEscherichia coli fed-batch fermentation for bovine somatotropin

Summary Optimum specific growth rate for the production of recombinant bovine somatotropin (bST) was investigated in fed-batchE. coli fermentation with a controlled specific growth rate. Maximum specific bST concentration based on cell mass decreases linearly with the controlled specific growth rate. Productivity of bST is expressed by a quadratic equation as a function of the specific growth rate and has a maximum value at =0.23 hr^–1.     

Growth of the toxic dinoflagellate Alexandrium minutum (Dinophyceae) using high biomass culture systems

Toxic dinoflagellates are important in natural ecosystems and are ofglobal economic significance because of the impact of toxic blooms onaquaculture and human health. Both the organisms and the toxins they producehave potential for biotechnology applications. We investigated autotrophicgrowth of a toxic dinoflagellate, Alexandrium minutum, inthree different high biomass culture systems, assessing growth, productivityandtoxin production. The systems used were: aerated and non-aerated2-L Erlenmeyer flasks; 0.5-L glass aerated tubes; anda 4-L laboratory scale alveolar panel photobioreactor. A range ofindicators was used to assess growth in these systems. Alexandriumminutum grew well in all culture conditions investigated, with amarked increase in both biomass and productivity in response to aeration. Thehighest cell concentration (4.9 × 10⁵ cellsmL^–1) and productivity (2.6 ×10⁴cells mL^–1d^–1) was achieved inthe aerated glass culture tubes. Stable growth of A.minutum in the laboratory scale alveolar panel photobioreactor wasmaintained over a period of five months, with a maximum cell concentration of3.3 × 10⁵ cells mL^–1, a meanproductivity of 1.4 × 10⁴ cells mL^–1d^–1, and toxin production of approximately 20g L^–1 d^–1 with weeklyharvesting.