Feeding in the rotifer Brachionus calyciflorus

Summary The laboratory feeding behavior of Brachionus calyciflorus varies depending upon the type of food cell available in suspension. When feeding on the yeast Rhodotorula glutinis, rotifers show a continuous increase in ingestion with increased cell density between 0.01 and 1000 g dry weight ml^-1. Effective clearance rates drop from ca. 50 l animal^-1 h^-1 to less than 0.5 l animal^-1 h^-1 over this food density range. When feeding on Englena gracilis, B. calyciflorus ingestion rates are constant between 1.0 and 100 g ml^-1 of available food, averaging close to 25 ng animal^-1 h^-1. The decrease in clearance rate is more striking than with R. glutinis, dropping from 45 l animal^-1 h^-1 at 0.1 g ml^-1 to 0.13 l animal^-1 h^-1 at 100 g ml^-1. Differences between the patterns obtained with the two food types indicate fundamental dissimilarities in the feeding behavior of this rotifer species when presented with these different foods.     

Ozone detoxification in the apoplasm and symplasm of spinach,broad bean and beech leaves at ambient and elevated concentrations of ozone in air

Spinach (Spinacia oleracea L.), broad bean (Vicia faba L.) and beech (Fagus sylvatica L.) plants were exposed to ozone at concentrations often measured in air during the summer months (120–300 g·m^–3) and antioxidants were determined in the leaf tissue and in the aqueous phase of the cell wall, the apoplasm. Concentrations of both reduced ascorbate (AA) and its oxidized form, dehydroascorbate (DHA), showed the tendency to increase transiently in the apoplasm of spinach leaves 6–24 h after starting fumigation with ozone. In beech leaves, apoplasmic AA and DHA increased 3–7 d after beginning of treatment. At the very high concentration of 1600 g O₃·m^–3, an increase of apoplasmic AA was already measured after 1 d in beech leaves. Apparently, spinach and beech leaves respond to oxidative stress by increasing AA transport into the apoplasm and by accelerating DHA export. In contrast to these observations, DHA accumulated during 3 d of fumigation with only 120 g O₃·m^–3 in the apoplasm of broad bean leaves, while AA contents did not increase. After termination of fumigation, the extracellular redox state of ascorbate normalized within 1 d. Glutathione could not be detected in the apoplasm of any of the three leaf species. Intracellular AA changed its redox state in response to exposure to elevated concentrations of ozone. After 4–6 weeks of fumigation with 200–300 g O₃·m^–3 an increase of intracellular DHA was measured in beech leaves. At the same time, chlorophyll contents decreased and characteristic symptoms of ozone damage could be observed. However, no significant change in the redox state of apoplasmic ascorbate could be detected in beech leaves. Evidently, detoxification of ozone by apoplasmic AA was insufficient to protect the leaf tissue. Fumigation with a high ozone concentration (1600 g·m^–3) caused an appreciable increase in the cellular contents of the oxidized forms of ascorbate and glutathione in beech leaves. Whereas in spinach leaves intracellular antioxidant contents and redox states were not altered during fumigation with 120–240 g O₃·m^–3, in broad bean leaves the intracellular DHA concentration increased and intracellular ascorbate became more oxidized after fumigation of the plants with 120 g O₃·m^–3. Apparently, broad bean leaves are more sensitive to ozone than beech and spinach leaves.Abbreviations AA ascorbate, reduced form - DHA ascorbate, oxidized form (dehydroascorbate) - FW fresh weight - GSH glutathione, reduced form - GSSG glutathione, oxidized form - IWF intercellular washing fluid - V_air intercellular air space volume of leaves - V_apo apoplasmic water volume of leaves This work was supported within the Sonderforschungsbereich 251 of the University of Würzburg.     

Insecticidal activity of avidin and streptavidin against four species of pest Lepidoptera

Two biotin-binding proteins, avidin and streptavidin, were found to be insecticidal to the larvae of four species of Lepidoptera – light brown apple moth, Epiphyas postvittana (Walker) (fam. Tortricidae), green-headed leaf-roller, Planotortrix octo (Dugdale) (fam. Tortricidae), brown-headed leaf-roller, Ctenopseustis obliquana (Walker) (fam. Tortricidae) and potato tuber moth, Phthorimaea operculella (Zeller) (fam. Gelechiidae). Mortality occurred in all species, but there was a wide range in susceptibility. P. operculella larvae were the most susceptible with an LC₅₀ of respectively, 2.3 g ml^–1 for avidin and 1.4 g ml^–1 for streptavidin after 9 days. E. postvittana larvae had an LC₅₀ of 43.4 g ml^–1 for avidin after 21 days, and C. obliquana larvae of 45.7 g ml^–1 for avidin after 28 days. Although significant mortality occurred in P.octo at the highest doses of avidin, there was no sufficient dose-mortality response to calculate an LC₅₀ for this species. For all species mortality curves were steep over a close range of doses followed by a plateau where mortality did not increase significantly with dose and did not reach 100%. Mortality was significantly affected by the amount of biotin in the diet on which the parental generation had been reared. Where this was rich in biotin, significant mortality of the offspring was much lower: larval offspring of a colony of E. postvittana, reared for five generations on a biotin-free diet had an LC₅₀ of 5.1 g ml^–1 after 14 days compared with 76.7 g ml^–1 for larvae from a colony reared on general purpose diet. The implications for use of these proteins to confer insect resistance on transgenic plants are discussed.     

Effects of GNA and other mannose binding lectins on development and fecundity of the peach-potato aphid Myzus persicae

Three mannose-binding lectins were assayed in artificial diets for their toxic and growth-inhibitory effects on nymphal development of the peach-potato aphid Myzus persicae. The snowdrop (Galanthus nivalis) lectin GNA was the most toxic, with an induced nymphal mortality of 42% at 1500 g ml^–1 (30 M) and an IC₅₀ (50% growth inhibition) of 630 g ml^–1 (13 M). The daffodil (Narcissus pseudonarcissus) lectin NPA and a garlic (Allium sativum) lectin ASA induced no significant mortality in the range 10–1500 g ml^–1, but did result in growth inhibition of 59% (NPA) and 26% (ASA) at 1500 g ml^–1 (40 M for NPA, 63 M for ASA). All three lectins were responsible for a slight but significant growth stimulation when ingested at 10 g ml^–1, reaching +26%, +18% and +11% over the control values for the garlic lectin, the daffodil lectin and the snowdrop lectin, respectively. GNA, as well as the glucose/mannose binding lectin Concanavalin A, were also provided at sublethal doses throughout the life cycle of the aphids, and effects on adult performance were monitored. Adult survival was not significantly altered, but both lectins adversely affected total fecundity and the dynamics of reproduction, resulting in significant reduction in calculated r _ms (population intrinsic rate of natural increase) on lectin-containing diets. These effects are discussed in relation to the use of transgenic plants expressing these toxic lectins for potential control of aphid populations.     

Comparative study of the growth of two strains ofNitrobacter in batch and continuous culture

Growth kinetics of 2Nitrobacter strains (N.w. and L) coexisting in the same soil are studied in batch and continuous culture. Monod's parameters are estimated numerically from experimental data in the case of the batch experiment, and from steady-state equations in the case of the chemostat. In both cases, the 2 strains show different values for their growth parameters. N.w. may be characterized by its high _max-K_s values, relative to strain L. But for each strain, _max is significantly lowered between batch and continuous culture. In this latter case, at N-NO₂ ^– concentrations less than 1.5g·ml^–1, the 2 strains exhibit similar growth rates showing that for concentrations of the limiting substrate prevailing in the soil, they may compete for this substrate.     

Binding of [3H]muscimol to calf cerebrocortical synaptic membranes and the effects of sulphur-containing convulsant and non-convulsant compounds

Endogenous and xenobiotic sulphur-containing convulsant and non-convulsant compounds containing structural moieties of, or bearing a structural resemblance to, GABA and homocysteine were tested in binding studies for their potency in displacing the GABA-mimetic [³H]muscimol from specific, high-affinity sites (K _d=3.6 nM;B _max=3.94 pmol/mg protein) on freeze-thawed, Triton-treated calf-brain synaptic membranes. The xenobiotic convulsants, 4-mercaptobutyric acid (MBA), 3-mercaptopropionic acid (3-MPA) and 2-mercaptopropionic acid (2-MPA) were found to be two-site competitive inhibitors exhibiting apparent inhibition affinity constants (K _i ^app ) of 5000 M, 3750 M, and 4800 M, respectively; while homocysteic acid (K _i ^app =4800 M) was shown to be a one-site partial competitive inhibitor. Intermediary metabolites of methionine: S-adenosyl-l-homocysteine,l-cysteine, the convulsantl-homocysteine, and its non-convulsant disulphide oxidation product, homocystine, were found to be one-site partial competitive inhibitors exhibitingK _i ^app values of 5750 M, 8350 M, 5000 M, and 510 M, respectively. The endogenous anticonvulsant neuroeffector, taurine, and the tripeptide, reduced glutathione (GSH) were shown to be, respectively, one-site (K _i=20 M) and two-site (K _i ^app =4300 M) competitive inhibitors of [³H]muscimol binding. These findings are discussed with regard to a previously proposed mechanism for the convulsant action of homocysteine.     

Effects of light on nitrate-limited Oscillatoria agardhii in chemostat cultures

The effects of the average light irradiance (I) on growth and nitrate uptake kinetics of the cyanobacterium Oscillatoria agardhii, in nitrate-limited chemostat cultures, were studied. Light was nonsaturating for I <9.4 Wm^–2, for all growth rates () studied. However, was throughout limited by the availability of nitrate. Under light-saturating conditions the kinetics of nitrate-limited growth could be adequately described by both the Monod and Droop equations. Under light-non-saturating conditions the internal nitrogen content (Q) was a function of both and I, for which new formulas were derived. The high uptake capacity (V _max) of nitrate-limited cells was independent of , but was significantly increased for cells growing at I <9.4 Wm^–2. The half-saturation constant for nitrate uptake (K _s ^u ) increased with increasing , but was independent of the prevailing light conditions. The effects of light during nitrate-limited growth were associated with the regulation in the nitrogen-containing pigments.The results reported herein have important consequences for the use of Q, K _s ^u and V _max values as indicators of nutrient-deficiency of natural populations.     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Utilization of H2O2 as the Oxygen Source by Bacteria of the Genera Pseudomonas and Rhodococcus

The growth of bacteria of the genera Pseudomonas and Rhodococcus in the presence of hydrogen peroxide as the sole source of oxygen was studied. The toxic effect of H₂O₂ in the concentration range of 100–200 g/ml was shown to extend the lag phase by two to three days. Apart from the peroxide toxicity, the bacterial growth was inhibited by the toxic effect of dissolved oxygen in concentrations over 100 g O₂/ml; in the presence of a liquid hydrocarbon phase, this effect was alleviated. Under decreased partial pressure of oxygen in the presence of hydrocarbons (12–15 vol %), culture growth was initiated at high initial concentrations of H₂O₂ (300 g/ml). When hydrogen peroxide concentrations exceeded 320 g/ml, no growth occurred, regardless of how much hydrocarbon was added.     

NADP+ reduction by a methanogen using HCOOH or H2 as electron donor

Summary The resting cells of methanogen strain HU could be used as biocatalyser for converting exoge nous NADP⁺ into NADPH, using either formate or hydrogen as electron donor. To enhance the conversion efficiency of NADPH from NADP⁺, several inhibitors of methylcoenzyme M reductase were used in order to avoid further oxidation of NADPH to CH₄. When methyl viologen (7.5 mol ml^-1) was added to the reaction mixture (17 mg of dry cells, 2 mg Triton X-100, 294 mol of Na-formate and 12 mol of NADP⁺ per ml reaction mixture), 9.6 mol ml^-1 NADPH (80% yield) could be produced in a 2-h reaction, compared with 7.2 mol ml^-1 NADPH (60% yield) in a 6-h reaction in the absence of methyl viologen. Molecular hydrogen istead of formate also served as electron donor to convert NADP⁺ into NADPH. A gas mixture of H₂/N₂ (75/25) yielded 9.8 mol ml^-1 NADPH (82% yield) in a 3-h reaction in the absence of formate, suggesting that H₂ might be a promising, inexpensive electron donor for this reaction system.     

Diagnosing lactic acid fermentation based on specific rates of growth,substrate consumption and product formation

The on-line calculated specific rates of growth, substrate consumption and product formation were used to diagnose microbial activities during a lactic acid fermentation. The specific rates were calculated from on-line measured cell mass, and substrate and product concentrations. The specific rates were more sensitive indicators of slight changes in fermentation conditions than such monitored data as cell mass or product concentrations.List of Symbols 1/h specific rate of cell growth - 1/h specific rate of substrate consumption - 1/h specific rate of product formation - ^* dimensionless specific rate of cell growth - ^* dimensionless specific rate of substrate consumption - ^* dimensionless specific rate of product formation - _max 1/h maximum specific rate of cell growth - _max 1/h maximum specific rate of substrate consumption - _max 1/h maximum specific rate of product formation - X g/l cell mass concentration - S g/l substrate concentration - S ^* dimensionless substrate concentration - S ₀ g/l initial substrate concentration - P g/l product concentration     

Control of yeast fed-batch process through regulation of extracellular ethanol concentration

At high growth rates, the biomass yield of bakers yeast (Saccharomyces cerevisiae) decreases due to the production of ethanol. For this reason, it is standard industrial practice to use a fed-batch process whereby the specific growth rate, , is fixed at a level below the point of ethanol production, i.e., _crit. Optimally, growth should be maintained at _crit, but in practice, this is difficult because _crit is dependent upon strain and culture conditions. In this work, growth was maintained at a point just above _crit by regulating ethanol concentration in the bioreactor. The models used for control design are shown, as are the experimental results obtained when this strategy was implemented. This technique should be applicable to all microorganisms that exhibit an overflow type metabolism.     

Isolation and characterization of a toxic intracellular protein from Vibrio parahaemolyticus

A toxic factor released from disrupted cells of Vibrio parahaemolyticus was partially purified by gel filtration after precipitation with (NH₄)₂SO₄ at 40% saturation. The factor, which was a thermostable protein of 63 kDa, lysed human erythrocytes at a concentration of 0.15 g ml^-1. Its LD₅₀ by intravenous injection into mice was 6.4 g. Fluid accumulated in suckling mice force-fed with the toxic material (1 to 25 g). Haemolytic activity, which occurred maximall at 37°C and pH 7.0 was enhanced by Ca²⁺, Cu²⁺ and Zn²⁺, each at 1 mm. Anti-toxic-factor serum agglutinated V. parahaemolyticus cells. The factor may play a role in the pathogenesis of V. parahaemolyticus infections and in the host's defence mechanisms against infection by the microorganism.     

A general equation for the evaluation of the error that affects the value of the maximum specific growth rate

A general equation is proposed to evaluate the absolute error that affects the maximum specific growth rate calculated from batch or continuous experiments. This error depends on the relative errors of the cell concentration measurements and on the duration of the test.Nomenclature X ₁ Cell concentration at the beginning of the exponential growth phase or of the washing-out period - X ₁ Lowest value of X ₁ due to experimental errors - X ₁ Highest value of X ₁ due to experimental errors - X ₂ Cell concentration at the end of the exponential growth phse or of the washing-out period - X ₂ Lowest value of X ₂ due to experimental errors - X ₂ Highest value of X ₂ due to experiment errors - Relative error that affects X ₁ - Relative error that affects X ₂ - t Exponential growth stage or washing-out duration - Asolute error that affects - Maximum specific growth rate - ₁ Lowest value of due to experimental errors - ₂ Highest value of due to experimental errors The author is with the Instituto Mauá de Technologia, Estrada das Lágrimas 2035, 09580-900, São Caetano do Sul, SP, Brazil     

Effect of zearalenone (F-2) on pea stem,maize root,and rat liver mitochondria

At 5 and 10 g ml^-1 concentration, zearalenone (F-2), a mycotoxin produced by a number of species of the genus Fusarium, causes an inhibition of the oxidative phosphorylation of isolated plant mitochondria, while at 20 and 40 g ml^-1 it causes uncoupling. However, when the mitochondria are pre-incubated for 20 min with F-2, the uncoupling appears to be the prevailing effect. F-2 is also able to inhibit the mitochondrial ATPase activity (Mg²⁺-dependent). Conversely, F-2 (40 g ml^-1) does not alter the ATP level of maize roots and only slightly affects the ATPase activity of pea stem and maize root microsomal fractions. In addition, F-2 (10–40 g ml^-1) inhibits ATP synthesis catalyzed by rat liver mitochondria. It is suggested that the phytotoxicity of F-2, also known for its ability to collapse the transmembrane electric potential of maize roots, may be mainly linked to its ability to increase the proton permeability of the cell, similar to the common uncouplers.Abbreviations F-2 zearalenone - DCCD N,N-dicyclohexylcarbodiimide - PCCP carbonyl cyanide, p-trifluoromethoxiphenylhydrazone - CBT Cerospora beticola toxin     

Menthol tolerant clones of Mentha arvensis: approach for in vitro selection of menthol rich genotypes

In vitro raised shoots of Mentha arvensis L. were screened for menthol tolerance level by growing them in media containing 0–100 g ml^–1 menthol. A total of 2850 regenerated shoots were step wise screened for menthol tolerance at the concentrations of 50 g ml^–1 followed by 60 and 70 g ml^–1. In this screening, only 30 individual regenerated shoots were able to survive. The clones from the primary screen were inoculated into rooting medium and, after rooting, transferred to pots in the greenhouse. Ultimately, these 30 menthol tolerant clones were multiplied and grown in the field in replicated plots of 2.5×2.5 m sizes. Twigs of 30 clones from the replicated trials were rechecked for tolerant phenotypes at a concentration of 70 g ml^–1 menthol wherein, these survived even after 7 days (secondary screening). These clones were checked for oil and menthol content and were found to be better than the control plants. Out of these 30 plants, five tolerated 80 g ml^–1 menthol (tertiary level screening) and were found to contain the highest amount of menthol per g leaf biomass. Molecular analysis through RAPD showed distinct variation in the profiles of these five plants, in comparison to the control. Using this method the relationship between the primer OPT 04, menthol tolerance and high menthol content character of the genotype was established. Further, a cultivar `Saksham' was released from the selections by CIMAP for superior performance.     

Responses of nitrogen-fixing and nitrate-supplied alfalfa (Medicago sativa L.) to iron chelates in an alkaline hydroponic medium

Ferric ethylenediamine di-(o-hydroxyphenylacetate) (FeEDDHA) and ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) were evaluated as Fe sources for hydroponic growth of alfalfa (Medicago sativa L., cv. Mesilla), either dependent on N₂ fixation or supplied with NO₃. The hydroponic medium was maintained at pH 7.5 by addition of CaCO₃. Nitrogen-fixing cultures were inoculated with Rhizobium meliloti 102 F51 and grown in medium without added nitrogen. After five to seven weeks of growth under greenhouse conditions, plants were harvested. Nitrogen fixation was measured by the acetylene reduction method.When FeEDDHA was supplied, growth of alfalfa, whether dependent on N₂ fixation or supplied with NO₃, was severely limited at concentrations typically used in hydroponic medium (10 or 20 M). Maximum yield of NO₃-supplied alfalfa was obtained at 100 M while maximum yield of N₂-fixing alfalfa was obtained in the range of 33 to 200 M FeEDDHA. Nodule fresh weights and N₂ fixation rates increased with FeEDDHA concentration up to 33 M and remained essentially constant up to 200 M. With FeHEDTA, maximum yields of both NO₃-grown and N₂-fixing alfalfa were obtained at 10 M. Growth of NO₃-supplied plants was inhibited at 200 M FeHEDTA while growth of N₂-fixing plants was inhibited at 100 M FeHEDTA. The numbers of nodules per plant increased between 3.3 and 10 M FeHEDTA; however, inhibition of nodule formation occurred at a concentration of 33 M or higher. Nodule weights per plant and N₂ fixation rates were depressed at 3.3 M as well as at 100 M FeHEDTA. The results suggest that alfalfa dependent on N₂ fixation is more sensitive to limited Fe availability than alfalfa supplied with NO₃.     

Somatic embryogenesis in callus cultures of Rosa hybrida L. cv. Landora

Callus was initiated from immature leaf and stem segments of rose (Rosa hybrida cv. Landora) and subcultured every four weeks on a basal medium of half-strength Murashige & Skoog (1962) salts plus 30 g l^-1 sucrose (1/2 MS) and supplemented with 2.2 M BA, 5.4 M NAA and 2.2–9.0 M 2,4-D. Embryogenic callus and subsequently somatic embryos were obtained from 8-week-old callus culture on 1/2 MS+2.2 M BA+0.05 M NAA+0.3 M GA₃+200–800 mg l^-1 L-proline. Long-term cultures were established and maintained for up to 16 months by repeated subculture of embryogenic callus on L-proline deficient medium. About 12% of cotyledonary stage embryos taken from cultures cold-stored at 8±1°C for 4 days germinated on 1/2 MS+2.2 M BA+0.3 M GA₃+24.7 M adenine sulphate.Abbreviations BA benzyladenine - NAA -naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid     

Cadmium interferes with steroid biosynthesis in rat granulosa and luteal cellsin vitro

Recently, cadmium has been described to disturb ovarian function in rats. In this paper the direct influence of cadmium on steroid production of ovarian cellsin vitro has been studied. Granulosa and luteal cells were obtained from proestrous and pregnant rats, and incubated with 0, 5, 10, 20 or 40 g ml^–1 CdCl₂ in the presence or absence of 0.1–1000 ng ml^–1 follicle stimulating hormone (FSH) or luteinizing hormone (LH) for 24 or 48 h. Production of progesterone (P) and 17-estradiol (E₂) by granulosa and that of P by luteal cells were measured by radioimmunoassay. In FSH-stimulated granulosa cell cultures, 5 and 40 g ml^–1 CdCl₂ suppressed P accumulation to 65 and 10%, respectively; accumulation of E₂ (at 5 g ml^–1 CdCl₂) decreased to 44%. P production of LH-supported luteal cells dropped to 86 and 66%, respectively, when 5 and 40 g ml^–1 CdCl₂ was added to the medium. No alteration in basal P accumulation occurred in granulosa and luteal cell cultures following incubations with 20 and 40 g ml^–1 CdCl₂, whereas basal E₂ production of granulosa cells was markedly diminished. It is concluded that CdCl₂ suppressing steroid synthesisin vitro exerts a direct influence on granulosa and luteal cell function.     

Effect of endogenous proteins on growth and antibody productivity in hybridoma batch cultures

It has been shown that some B-cell hybridomas secrete autocrine factorsin vitro which can influence cell metabolic processes. Rather than screen specifically for suspected cytokines, that may or may not affect our cell line, we have examined the lumped effects of intracellular and secreted factors on cell proliferation and monoclonal productivity in hybridoma batch cultures. Firstly, supplements of total soluble intracellular proteins combined with other intracellular metabolites were found to both decrease the specific growth rate and increase the antibody production rate at higher concentrations in batch culture. This is an important consideration in high cell density cultures, such as perfusion systems, where a reduction of growth by the presence of intracellular factors may be compensated by an increase in MAb production. In addition, flow cytometry data revealed that the average cell cycle G₁ phase fraction was unaffected by the variation in the maximum specific growth rates during the exponential growth phase, caused by the addition of intracellular factors; this suggests that higher MAb productivity at lower growth rates are not a result of cell arrest in the G₁ phase. Secondly, secreted extracellular proteins larger than 10,000 Daltons, which were concentrated from spent culture supernatant, were shown to have no significant effect on growth and specific MAb productivity when supplemented to batch culture at levels twice that encountered late in normal batch culture. This indicates that endogenous secreted cytokines, if at all present, do not play a major autocrine role for this cell line.Abbreviations FBS fetal bovine serum - MAb monoclonal antibody - MWCO molecular weight cut off - SDS-PAGE sodium dodecyl-sulphate-polyacrylamide gel electrophoresis - k _d exponential phase death rate, h^–1 - q _MAb exponential phase specific monoclonal antibody productivity, pg/(cell·h) - t time, h - X _d dead cell density, cells/mL - X _v viable cell density, cells/mL - specific growth rate, h^–1 - _{max app} apparent maximum specific growth rate, h^–1 - _max maximum specific growth rate, h^–1 _max = _{max app + Kd}