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  • 1
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The retroviral titer obtained from the pMFG/ψCRIP producer cell line is determined by a dynamic interplay of vector production and deactivation rates. Both these rates are influenced by temperature. It was determined that; (i) the retroviral half-lives are strongly influenced by temperature and the temperature dependency can be described by the Arrhenius equation with an activation energy of 39 kcal/gmol; (ii) the actual retroviral vector productivity per cell is highest at 37 °C with retroviral production rate of 24.4(±7.0; ± standard deviation) colony forming unit (CFU)/cell/day; (iii) the dynamic interplay of these two factors produces an optimal temperature of 34 °C for pMFG/ψCRIP cells under the culture conditions used; and (iv) the cellular growth rate is highest at 37 °C at 26.8 hr doubling time. Taken together, these parameters can be used to optimize a two-step retroviral production protocol, where the cells are first grown under optimal growth conditions (37 °C) and second, the virus is produced at 34 °C to yield the highest titer. These results have significant implications for optimal retroviral production protocols.
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  • 2
    ISSN: 1435-1536
    Keywords: Key words Aging ; Poly(vinyl alcohol) ; Gel ; Syndiotacticity ; High molecular weight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The properties of the aged gels of high molecular weight syndiotacticity-rich poly(vinyl alcohol)s (HMW S-PVAs) with different syndiotactic diad (s-diad) contents were investigated. HMW S-PVA gels with s-diad content of 61.5% and 58.2% showed the rapid increases of the syneresis and the turbidity from the early stage of aging time, which is ascribable to the phase separation, while that with s-diad content of 55.7% did not. From the morphological study, it was confirmed that the phase separation in HMW S-PVA gel with s-diad content of 61.5% occurred without the liquid-liquid phase separation in sol state, whereas both the liquid-liquid phase separation in sol state and the subsequent phase separation in gel state occurred in the case of HMW S-PVA gel with s-diad content of 58.2%. On the other hand, HMW S-PVA gel with s-diad content of 55.7% showed neither the liquid-liquid phase separation in sol state nor the phase separation in gel state in the long period of time. It was also confirmed from wide angle X-ray diffractogram that the crystallization was accompanied by the phase separation in gel state in the aging process of PVA gel. However, the crystallization was hindered by the fast network formation at the initial stage of time. Later the syndiotacticity promoted the crystallization. The tensile modulus of HMW S-PVA gel with higher syndiotacticity increased more significantly with time.
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  • 3
    ISSN: 1432-2048
    Keywords: Arginine decarboxylase ; Auxin in somatic embryogenesis ; Cell culture (polyamines) ; Dnucus (polyamines in embryogenesis) ; Embryogenesis somatic ; Polyamine ; S-Adenosylmethionine decarboxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Polyamine levels and the activities of two polyamine biosynthetic enzymes, arginine decarboxylase (EC 4.1.1.19) and S-adenosylmethionine decarboxylase (EC 4.1.1.50), were determined during somatic embryogenesis of carrot (Daucus carota L.) cell cultures. Embryogenic cultures showed severalfold increases in polyamine levels over nondifferentiating controls. A mutant cell line that failed to form embryos but grew at the same rate as the wild-type line also failed to show increases in polyamine levels, thus providing evidence that this increased polyamine content was in fact associated with the development of embryos. Furthermore, inhibition of these increases in polyamines caused by drugs inhibited embryogenesis and the effect was reversible with spermidine. The activities of arginine decarboxylase and Sadenosylmethionine decarboxylase were found to be suppressed by auxin; however, the specific effects differed between exogenous 2,4-dichlorophenoxyacetic acid and endogenous indole-3-acetic acid. The results indicate that increased polyamine levels are required for cellular differentiation and development occurring during somatic embryogenesis in carrot cell cultures.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four ...
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  • 5
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract New secretion vectors containing the Bacillus sp. endoxylanase signal sequence were constructed for the secretory production of recombinant proteins in Escherichia coli. The E. coli alkaline phosphatase structural gene fused to the endoxylanase signal sequence was expressed from the trc promoter in various E. coli strains by induction with IPTG. Among those tested, E. coli HB101 showed the highest efficiency of secretion (up to 25.3% of total proteins). When cells were induced with 1 mM IPTG, most of the secreted alkaline phosphatase formed inclusion bodies in the periplasm. However, alkaline phosphatase could be produced as a soluble form without reduction of expression level by inducing with less (0.01 mM) IPTG, and greater than 90% of alkaline phosphatase could be recovered from the periplasm by the simple osmotic shock method. Fed-batch cultures were carried out to examine the possibility of secretory protein production at high cell density. Up to 5.2 g/l soluble alkaline phosphatase could be produced in the periplasm by the pH-stat fed-batch cultivation of E. coli HB101 harboring pTrcS1PhoA. These results demonstrate the possibility of efficient secretory production of recombinant proteins in E. coli by high cell density cultivation.
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  • 6
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Although many studies have examined the influence of culture conditions on the production and composition of polysaccharides, little is known about the factors influencing the quality of exopolysaccharides (EPS). In this work we studied the effect of yeast extract on the production, composition and molecular weight of the EPS zooglan produced by Zoogloea ramigera 115SLR. This bacterium was grown on a new completely defined synthetic medium and on a medium containing yeast extract. Growth and polysaccharide production performances were comparable on the two media with a glucose to exopolysaccharide conversion yield of 35% (g/g). The polysaccharides produced on these two media have an identical composition but a different molecular weight and molecular weight distribution. The yeast extract medium leads to a more homogeneous polysaccharide solution.
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  • 7
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Pseudomonas 135, a facultative methylotroph, was cultivated on methanol as a sole carbon and energy source for the accumulation of poly-β-hydroxybutyric acid (PHB). The cells grew fairly well on minimal synthetic medium containing 0.5% (v/v) of methanol at pH 7.0 and 30° C. The maximum specific growth rate was determined to be 0.26–0.28 h−1 with a growth yield of 0.38 in the optimized growth medium. For stimulation of PHB accumulation in the cells, deficiency of nutrients such as NH inf4 sup+ , Mg2+ and PO inf4 sup3− was crucial even though cell growth was significantly suppressed. The PHB content of a 40-h culture was determined to be 37% of the total cell mass in NH inf4 sup+ -limited medium, 42.5% on Mg2+-deficient medium, and 34.5% on PO inf4 sup3− -deficient medium. The maximum content of PHB in the cells could reach 55% in NH inf4 sup+ -limited fed-batch culture. The average relative molecular eight determined by gel permeation chromatography was 3.7 × 105 in NH inf4 sup+ -limited culture, 2.5 × 105 in Mg2+-deficientmedium, and 3.1 × 105 in PO inf4 sup3− -deficient medium. Polydispersity determined in each culture was relatively high (about 10–11). The solid PHB had a melting temperature of 173° C.
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