摘要:

AbstractEffects of inoculum cell density on mammalian cell growth in culture have been observed in a variety of experimental systems. Although these effects have been attributed generally to medium conditioning by the cells, there has previously been no quantitative theory proposed for this phenomenon based on developments in molecular and cell biology. In this article, we offer such a theory founded on the regulatory action of autocrine growth factors. A particularly relevant example of these is platelet‐ derived growth factor (PDGF), which is produced by fibroblastic cells in response to stimulation by transforming growth factor β (TGFβ), a common serum constituent, and provides a mitogenic signal for the same cells. A simple mathematical model for the production, diffusive transport, and binding of autocrine growth factors to cell surface receptors, coupled to a model for the dependence of cell proliferation on growth factor receptor binding allows prediction of initial cell population growth rate as a function of inoculum cell density. We focus on situations involving anchorage‐dependent cell growth, in which the cells are attached to a surface. A number of clear results are obtained, most notably the following: 1) for cells cultured on spherical microcarrier bead surfaces, the inoculum cell density needed to produce a given growth rate islinearly proportionalto the bead radius; and 2) all other factors being equal, the inoculum cell density on a unit surface area basis needed to produce a given growth rate is greater for spherical microcarrier surfaces than for flat culture dish surfaces. These two results are consistent with the experimental observations of Hu and coworkers1,2for fibroblast growth in minimal medium plus serum. The model also allows elucidation of the influence of other system parameters, both biological and physical, on initial cell proliferation rate and the inoculum cell density depen

ISSN:0006-3592    

DOI:10.1002/bit.260331102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractAcoustic resonance densitometry (ARD) provides a highly reproducible and stable method for on‐line measurement of culture biomass density. The technique provides a direct determination of changes in relative density of culture medium and cell mass. At cell concentrations higher than 106cells mL−1this method can replace cell counts and provide a continuous measure of total cell mass. In cultures of hybridomas or U937 human lymphoma cells, the ARD value correlates well with cell number except when the average cell size changes during culture. It is argued that cell mass determined by ARD rather than cell number should be used as the basis for measurements of specific biological activ

ISSN:0006-3592    

DOI:10.1002/bit.260331103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractPenicillin was recovered from mycel‐containing fermentation broth by direct reactive extraction into a counter‐current extraction decanter, Type CA 226–290 of the Westfalia Separator Co., at room temperature via steady state operation. Penicillin concentrations in the feed varied from 3 to 41 g L−1, Amberlite LA‐2 carrier concentrations from 7 to 20 g L−1and/or DITDA carrier concentrations from 7.2 to 84 g L−1, the LA‐2‐to‐penicillin mole concentration ratio from 4 to 6.4, and/or the DITDA‐to‐penicillin mole concentration ratio was maintained at 2. The throughputs of the fermentation broth (520 to 880 L h−1) of the solvent phase (200 to 860 L h−1) and the over all throughput (800 to 1750 L h−1) were high. Extraction degrees of 72 to 96% were achieved between pH 4.6 and 5.1. Without carriers in the same pH range, extraction degrees of only 17 to 19% were attained. By reducing the pH to 2.3 and in the absence of carriers, the degree of extraction was increased to 61%. However, during the extraction, 6.5% of the penicillin decomposed. At these high throughputs, the steady state was attained within 1 to 4 min. Through the mechanical stress, the length of the hyphae was reduced and the protein content of the broth was increased by 50 to 100%. However, this protein content had no appreciable infl

ISSN:0006-3592    

DOI:10.1002/bit.260331104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThis article treats the basic problem of selection of experimental conditions for microbiological experiments for evaluation of newly isolated bacterial strains, mutants, or plasmid/strain combinations. For this purpose shake flask experiments in a 210‐4confounded factorial design at resolution IV with four blocks of 16 flasks were used. The design was used for testing of two new strain/plasmid combinations (E. coliMT 102/403‐SD2 and W 3110/403‐SD2) i.e., both strains with the same plasmid 403‐SD2. Both strains were integrated in the design, so both strains were tested with nine factors (temperature, aeration, glucose, initial pH, pH regulation, reduced aeration, chloramphenicol, acetate, and glycerol). With both strains the interaction between initial pH and reduced aeration had a significant influence on the yield of the recombinant‐DNA product nuclease. There was more than a factor of 10 between lowest and highest yield of product. In this interactive system the strains reacted differently. MT 102/403‐SD2 had highest yields at high initial pH (8.4) and no reduction in aeration, whereas W 3110/403‐SD2 had highest yields of nuclease at low initial pH (7.4) and reduced aeration (rubber stopper inserted after cultivation for 12 h). These data (and previous work) clearly demonstrate that it is impossible to suggest a simple set of experimental conditions for testing of new plasmid/strain combinations. It is clear that the exclusive application of a standardized growth technique e.g., LB‐medium at 37°C at an unspecified and uncontrolled aeration level, may lead to wrong conclusions on properties and potentials of now plasmid/strain combinations and may lead to rejection of useful str

ISSN:0006-3592    

DOI:10.1002/bit.260331105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe continuous α‐chymotrypsin‐catalyzed peptide synthesis of kyotorphin, tyrosyl‐arginine, via theNαformyltyrosyl‐arginine propyl ester is described. For continuous process development, two reaction systems were studied: immobilized α‐chymotrypsin covalently bound to Eupergit C packed in a column, and soluble α‐chymotrypsin utilizing an enzyme membrane reactor. Selectivities and kinetic parameters are discussed. The use of soluble enzyme in an enzyme membrane reactor proved superior to the covalently immobilized enzyme. A significant loss of enzyme activity and a certain decrease of selectivity was observed during immobilization. It was shown that the addition of organic solvent, in this casen‐propanol, causes a severe diminuation of th

ISSN:0006-3592    

DOI:10.1002/bit.260331106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA dynamic method is proposed forklameasurement in aerated and agitated reactors, in which a change in the total pressure in the reactor by approximately 20% leads to a simultaneous change in the oxygen concentration in all the bubbles in the dispersion. This procedure suppresses the influence of nonideal mixing of the gas phase on the kla value. Other dynamic methods so far used do not possess this advantage. They are based on a step change in oxygen concentration in the entering gas, where the interfacial nitrogen transport and the finite rate of the concentration change propagation into the individual bubbles in the dispersion can cause an error in the reportedklavalues of more than hundreds of percent. The reliability of the pressure method is tested by comparison both with the standard dynamic method, in which pure oxygen is absorbed in a liquid from which all other gas components were previously removed, and with the steady‐state sulphite method. The signal of the oxygen probe used in the experiments must be independent of the pressure. A test for this in dependence is described. The pressure method is also suitable for large‐scale reactors since the necessary pressure changes are sufficiently small and, morever, air can be u

ISSN:0006-3592    

DOI:10.1002/bit.260331107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractGluconobacter suboxydansIFO 3290 was immobilized by adsorption on ceramic honeycomb monolith and continuous production of free gluconic acid from glucose was performed in an aerated reactor. The effects of reactor residence time, aeration rate, and glucose concentration were investigated on the gluconic acid yield. Observation of SEM photographs revealed that the cells were adsorbed with a high density not only on the outer surface of the support but also on the inner surface of large pores. From measurement of the number of the adsorbed cells, it was elucidated that the biofilm comprised a monolayer or bilayer of the cells. Maximum specific rate of growth was estimated for the free and adsorbed cells, and the adsorbed cells were found to grow at a fast rate compared with the free cells. In the continuous fermentation performed for one month at the glucose concentration of 100 kg/m3, reactor residence time of 3.5 h and aeration rate of 900 cm3/min, the activity of the adsorbed cells was appreciably stable. The high productivity of 26.3 kg/(m3‐reactor · h) was attained with the gluconic acid yield of 84.6% and glucose conversion of 9

ISSN:0006-3592    

DOI:10.1002/bit.260331108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractAn adaptive control algorithm for the on‐line determination of optimal temperature or pH for biomass production in a continuous fermentor is presented. The algorithm requires no prior information and uses a dynamic Hammerstein model to identify parameters and to estimate an optimal steady‐state control value. A check of the estimated performance measure second derivative is included to ensure that the target extremum is an optimum. The process is driven towards this optimum with a variable step size that depends on the quality of the on‐line identified model. Numerical simulations are performed on a dynamic chemostat model that incorporates a metabolic time delay. The algorithm successfully finds the optimum temperature or pH values and maintains the reactor at the optimum steady

ISSN:0006-3592    

DOI:10.1002/bit.260331109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractAn experimental study was undertaken to identify and quantitate the effects of plasmid amplification and recombinant gene expression onEscherichia coligrowth kinetics. Identification of these effects was possible because recombinant gene expression and plasmid copy number were controlled by different mechanisms on plasmid pVH106/172. Recombinant gene expression of the lactose operon structural genes was under the control of thelacpromoter and was activated by the addition of the chemicals, IPTG and cyclic AMP, to the fermentation medium. Plasmid content was amplified in a separate fermentation by increasing culture temperature since the plasmid replicon was temperature‐sensitive. A final fermentation was performed in which both plasmid content and recombinant gene expression were induced simultaneously by adding chemicals and raising the culture temperature. Recombinant growth rates were found to be reduced by the expression of high levels of recombinantlacproteins in the chemical induction experiments and by the amplification of plasmid levels in the temperature induction experiment. High expression of recombinantlacproteins following chemical induction was accompanied by a loss in recombinant cell viability. In the plasmid amplification experiment, the recombinant cells did not lose viability but the recombinant product yields were much lower than those achieved in the chemical induction experiments. Combining temperature and chemical induction increased the recombinant product yield by a factor of 4400 but also lowered cellular growth rates by 70

ISSN:0006-3592    

DOI:10.1002/bit.260331110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe effects of various factors in culture medium on the phenolics production from cultured tobacco cells (free and immobilized) were studied. It was found that removing the growth hormone from the medium increased the productivities of phenolics for both free and immobilized cultures. Low initial sucrose concentration in the medium restricted growth and resulted in high cellular productivities of the phenolics for freely suspended cells, but not for the immobilized cells. Addition of 1.4% DMSO to standard culture medium greatly increased phenolics productivities without affecting cell viability in both free and immobilized cell cultures. Continuous operation of a packed‐column reactor of the immobilized cells was achieved for 500 hours. Aeration was accomplished by diffusing pure oxygen through silicone tubing placed inside the reactor. It was found that prolonged cell viability was contingent upon initially operating the reactor with total recycle for several days, and then introducing fresh feed while maintaining a high recycle rate. Immobilized cells packed in a continuous column reactor achieved productivities more than twice that achieved in any batch ru

ISSN:0006-3592    

DOI:10.1002/bit.260331111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY