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  • 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 inhibitory effect of various alkanols, benzyl alcohol and phenethyl alcohol on the growth rate of Clostridium acetobutylicum ATCC 824 was investigated. Inhibition of cell growth was studied by treating cultures with varied concentrations of alcohols. There was a threshold concentration above which growth inhibition occurred. The degree of inhibition was a linear function of the alcohol concentration used. The natural logarithm of the inhibition constant was shown to be: (1) a linear function of the chain length of the alkanols, (2) a linear function of the natural logarithm of the octanol/water partition coefficient for both aliphatic and cyclic alcohols.
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  • 3
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary A mathematical model of batch acetonobutylic fermentation under glucose limitation is proposed. Making use of available information on the physiology of the process this model correctly predicts the two phases of growth and product formation observed at low extracellular pH, with production of butanol and acetone predominating in the final stage and butyrate and acetate production predominating at more neutral pH. A fair agreement between the prediction and experiments performed in different laboratories at different substrate concentrations and pH was achieved.
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  • 4
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Survival of alginate-entrapped cells of Azospirillum lipoferum was studied during dehydration using a dry air stream and during prolonged storage at various constant water activity values (aw). During the drying operation, the viability loss remained almost constant from the initial water content to 0.35 g water/g dry weight (DW) corresponding to a 98.5% water removal, strongly increased until a water content of 0.25 g/g DW and then stopped until the end of the drying operational (final aw 0.18). A water content of 0.25 g/g DW (aw=0.55) corresponded to the critical point of the moisture sorption isotherm curve from which water became restricted to the dry material. A high drying rate (5 g/g DW per hour) was shown to be more detrimental for cell viability than a low drying rate (1.18 g/g DW per hour). When the product was stored in a closed chamber with a regulated aw (0.23), the number of living cells decreased during a short period (less than 15 days) corresponding to the product aw stabilization, and then remained constant for more than 150 days. In addition, cell survival during storage was not affected by aw values in the range 0–0.55. Above aw=0.55, the higher the aw and the storage duration, the lower the residual survival percentage. The influence of the drying and storage conditions on the cell death rate are discussed with regard to both the mechanisms generally involved in viability loss and the hydration properties of water.
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  • 5
    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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  • 6
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Batch and continuous fermentations of methanol/CO2 by the acidogenic Eubacterium limosum were modified with respect to growth and production of organic acids by the choice of reducing agent. Titanium (III) citrate enhanced the maximum specific growth rate (μmax) and the yield of butyrate at the expense of acetate, whilst Na2S was toxic but able to provoke homobutyric fermentations. In general, the lower the redox potential prior to inoculation the higher the CO2 consumption though not to the detriment of butyrate synthesis. It would seen likely that the redox potential of the culture medium plays a role in either maintaining a high level of reduced co-enzymes and/or altering the relative contribution of the proton (ΔpH) and ionic (Δψ) gradients to the proton motive force, in such a way that butyrate production is favoured.
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  • 7
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An unsaturated fatty acid auxotroph of the oleaginous yeast Apiotrichum curvatum, named UfaM3, blocked in the conversion of stearic to oleic acid was cultivated in single-stage continuous culture. The influence of consumed carbon to nitrogen ratios (C/N ratios, g g−1) obtained at various dilution rates (D) on fatty acid (FA) accumulation and its profiles were studied. In continuous culture in N-limited medium a maximum FA accumulation of 45.6% (g g−1 of dry biomass) was obtained at an optimal D of 0.049 h−1, recording an efficiency of substrate conversion of 0.48 g g−1 and 0.22 g g−1 for biomass and lipids, respectively. The quality of lipid approached cocoa butter at an optimal C/N ratio of between 20 and 30. The C/N ratio in the incoming medium was 38.5 g g−1 with 30 g l−1 of glucose and both C and N sources were completely consumed at a critical D of ≤ 0.07 h−1. The stability of the mutant was demonstrated in the steady-state conditions of the chemostat with regard to the FA composition of its lipids.
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  • 8
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Growth ofEubacterium limosum B2 on methanol-CO2 was dependent upon the pH; optimum growth rates were obtained at pH 7.3–7.4. Carbon dioxide, a necessary cosubstrate for methylotrophic growth on methanol, was a determining factor for both growth and the nature of the organic acid produced. The coefficient of affinity for CO2 was not affected by variations in pH if calculated relative to the concentration of hydrogen carbonate (16 mM). Similarly the conversion rate for methanol into acetic acid and butyric acid remained constant regardless of the level of pH with a fixed concentration of hydrogen carbonate. The metabolism ofE. limosum B2 grown on methanol-CO2 was regulated by the HCO 3 - concentration in the medium.
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  • 9
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Serial enrichment was used to obtain a strain ofClostridium acetobutylicum demonstrating a 40% increase in tolerance to added butanol and a further 17% improvement in the ability to produce butanol. The glucose and the butyrate consumption were higher for the G1 variant than for the wild-type strain. In consideration of the higher butanol tolerance, a disappointly low titer of butanol was produced by the new strain. This can be explained by the higher level of autobacteriocin produced by G1. Control of autobacteriocin production appears to be one of the key factors limiting the potential of the acetone butanol fermentation.
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  • 10
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Clostriodium acetobutylicum ATCC 824 produced an autobacteriocin. A precise method for the quantitative estimation of the autobacteriocin activity is described. Release of the autobacteriocin occurs at the end of the exponential phase of growth. The producer strain and four strains of bacteria belonging to the family Bacillaceae were sensitive to the bacteriocin. The thermolabile autobacteriocin was stable between pH 3.5 and pH 5. This autobacteriocin has a bacteriolytic effect which increases with the age of the cells and with the butanol concentration. This autobacteriocin seemed to be an autolysin and a possible regulation of its action by lipoteichoic acids is discussed.
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