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  • 1985-1989  (10)
  • 1970-1974  (1)
  • 1
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Le mécanisme d'assimilation des hydrocarbures par une levure, Candida lipolytica est étudié au moyen de l'analyse cinétique de la croissance du microorganisme et de la disparition du substrat hydrocarboné. Les hydrocarbures utilisés sont des n-paraffines. On ajoute au milieu soit un seul hydrocarbure (n-tetradécane ou n-hexadécane), soit un mélange binaire (n-dodécane et n-heptadécane), soit un mélange complexe (du n-undécane au n-octadécane). Contrairement à d'autres auteurs, nous pensons qu'il est peu probable que l'essentiel de la réaction s'effectue par contact des gouttes de substrat et des microorganismes puisque l'on observe des retards d'assimilation de certains hydrocarbures: ceux de faible poids moléculaire (les plus solubles) sont assimilés plus rapidement. Il semble donc que l'assimilation se fasse en grande partie à partir d'hydrocarbures préablement solubilisés.
    Notes: Summary The mechanism of hydrocarbon uptake by a yeast, Candida lipolytica has been studied by means of the kinetic analysis of micro-organism growth and substrate assimilation. Hydrocarbons used as only source of carbon are normal alkanes either pure (n-tetradecane or n-hexadecane) or in mixture of two paraffins (n-dodecane and n-heptadecane) or eight paraffins (n-undecane to n-octadecane). In these last cases delays in n-alkanes consumption are observed. They show that the most soluble substrates (lower molecular weight) are first consumed. In opposition to other authors we think that there is little probability for main reaction occurring by direct contact between drops and micro-organisms. The evidence indicates that n-alkanes are mainly utilized in the dissolved state.
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  • 2
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The effect of various culture conditions on growth kinetics of an homofermentative strain of the lactic acid bacterium Streptococcus cremoris were investigated in batch cultures, in order to facilitate the production of this organism as a starter culture for the dairy industry. An optimal pH range of 6.3–6.9 was found and a lactose concentration of 37 g·l-1 was shown to be sufficient to cover the energetic demand for biomass formation, using the recommended medium. The study of the effect of lactic acid concentration on growth kinetics revealed that the end-product was not the sole factor affecting growth. The strain was characterized for its tolerance towards lactic acid and a critical concentration of 70 g·l-1 demonstrated. With the product yield of 0.9 g·g-1 at non-lactose limiting conditions the lactic acid concentration of 33 g·l-1 could not explain the low growth rates obtained, implicating a nutritional limitation.
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  • 3
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Catharanthus roseus cells were grown at various aeration rates using normal or CO2-enriched air. Kinetic data showed a detrimental effect of the increase of the gassing rate on the growth characteristics due to CO2 stripping. When the CO2 partial pressure in the culture was maintained at a constant level of 20 mbar, better growth and enhanced conversion yields were obtained.
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  • 4
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Catharanthus roseus cells were grown at various aeration rates using normal or CO2-enriched air. Kinetic data showed a detrimental effect of the increase of the gassing rate on the growth characteristics due to CO2 stripping. When the CO2 partial pressure in the culture was maintained at a constant level of 20 mbar, better growth and enhanced conversion yields were obtained.
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  • 5
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Growth of a lactic streptococcus was studied in continuous cultures, under various conditions of medium richness, without carbon source limitation, and with a large range of dilution rates. Increasing the concentrations of growth factors and protein nitrogen sources resulted in increased volumetric productivities of biomass and lactic acid with maximum values in the 0.3–0.4 h−1 dilution rate range. Growth was shown to be dependent on both the inhibitory effect of lactic acid and the availability of certain nutrients, as has previously been shown for batch cultures.
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  • 6
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary In batch cultures of Streptococcus cremoris growth parameters, especially the specific growth rate and its alteration during time-courses of fermentation, were found to be dependent on the culture conditions, in particular the inoculum size and medium composition. It was demonstrated that growth was subject to two main factors, inhibition by lactic acid and limitation by nutritional compounds, the first effect being strongly dependent on medium composition. The tolerance of the strain towards lactic acid was characterized, and critical values of the end-product were related to the concentration of yeast extract and bactotryptone in the medium. After taking into consideration the inhibitory effect of lactic acid, the level of nutritional limitation accounted for the change in specific growth rate during time courses of the culture.
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  • 7
    ISSN: 1432-203X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The limitation of growth of Catharanthus roseus cells was investigated with a view to their entrapment in a Ca-alginate matrix. An examination of the effects of lowered 2,4-D and phosphate concentrations on cell viability and indole alkaloid biosynthesis enabled a growth limiting and product formation stimulating medium to be designed. Entrapped cells showed a retention of both respiratory activity and biosynthetic capacity over an extended period of time compared with free cells. Evidence is presented which suggests that immobilization in Ca-alginate beads acts to stabilize cells, resulting in enhanced product accumulation.
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  • 8
    ISSN: 1573-5044
    Keywords: Lipophilic amines distribution ; Ajmalicine release ; pH gradients ; Catharanthus roseus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During growth, Catharanthus roseus cells exhibit an acidification of the culture medium that may be controlled by Ca2+. With a view to enhance the productivity of alkaloids by plant cells, the effect of extracellular pH modifications on the excretion processes has been investigated. Ca2+ dependent proton pumping leads to the release of various lipophilic amine-like compounds (benzylamine, methylamine, nicotine) initially accumulated by the cells, but also facilitates the excretion of endogenous ajmalicine. Once released in the medium, these compounds are however taken up again by the cells, probably as the charged form. For the alkaloid contained in C. roseus some evidence suggests that the diffusible form comes from the cytosolic compartment and not from the storage vacuoles. This appears to be a major production limitation to the use of pH gradients in order to favour alkaloid excretion.
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  • 9
    ISSN: 1573-5044
    Keywords: Catharanthus roseus ; cell suspension culture ; enzyme activities ; carbon dioxide partial pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In vitro enzyme activities of glycolysis, pentose-phosphate pathway and dark CO2 fixation were assayed in batch cultures of heterotrophic Catharanthus roseus cells under various gassing rates and partial pressures of carbon dioxide. Detrimental effects of low pCO2 culture conditions on the growth characteristics could be linked to marked changes in levels of enzymes of primary metabolism during growth. The enzyme levels observed during the early stages of growth were found to be more stable when a constant pCO2 (20 mbar) was maintained and enabled exponential growth to be reached more rapidly. The importance of carbon dioxide as a “conditioning factor” of the culture medium is discussed.
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  • 10
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Growth parameters of Catharanthus roseus in suspension cultures were examined under various pCO2 conditions. In CO2-enriched environments (up to 2 %) for Erlenmeyer flask cultures, enhanced maximum growth rates and conversion yields were observed. Fermenter cultures with a constant pCO2 of 2 %, gave high conversion yields although no growth-promoting activity was observed. High aeration rates led to decreased rates of growth due to CO2 stripping.
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