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  • 1
    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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  • 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 a Schizosaccharomyces pombe strain were investigated in order to facilitate the potential use of this organism in enology. The effect of ethanol was characterized as a 80 g·l−1 critical concentration. An optimal pH range of 3.5–4.0 was found. Growth was slightly affected by malic acid at pH 3.0 but was shown to decrease drastically at pH 5.5. Aerated cultures had increased rates of growth and malate degradation than those grown under anaerobiosis, although the specific rate of malate degradation remained fairly constant. Taking into account biomass synthesis data it would seem likely that under anaerobiosis malate can replenish the Krebs' cycle for amphibolic precursor synthesis and hence avoid potential growth 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 The effect of culture conditions, especially nitrogen/carbon (N/C) ratio and temperature, on acyl lipid profiles in the oleaginous yeast Rhodotorula glutinis NRRL Y 1091 have been investigated. Cultivation of the microorganism under N-limited conditions (N/C 〈 0.14 g/g) resulted in enhanced fatty acid (FA) cell content but a reduced relative amount of polyunsaturated fatty acids (PUFA). The maximal FA productivity was obtained for a 0.025 N/C ratio resulting from the arrangement between the specific rate of FA synthesis and the concentration of lipid-free biomass. Under nitrogen-non-limiting conditions, cells grown at lower temperatures had a higher PUFA content and the maximal productivity of α-linolenic acid was obtained by shifting the temperature of the culture from 30° C to 25° C.
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  • 4
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The effects of nitrogen (N), phosphorus (P), zinc (Zn) or iron (Fe) limitations on lipid and especially α-linolenic acid (ALA) synthesis in the oleaginous yeast Rhodotorula glutinis have been investigated. Exhaustion of the limiting element in the medium resulted in an enhancement of both the fatty acid cell content (FA/X) and the corresponding productivity. Except for Fe-limited media, lipid accumulation was always coupled with an increase in the yield of ALA synthesis, whereas in all the limiting conditions the productivity of ALA declined. Kinetic investigations showed that this decline resulted from a sharp decrease in the specific rates of ALA synthesis associated with slowing down of growth. A comparative study showed that the highest yields and specific rates of fatty acid and ALA synthesis were induced by P-limitation early in the lipid accumulation phase. However, above a FA/X of 15%, N-limiting conditions become more attractive for producing lipids. During P-limited growth a down-shift of temperature from 30° C to 25° C was shown ao reduce the range of FA/X values at which the specific rate of fatty acid synthesis was maximal but without any other effect on fatty acid formation. In contrast, the decreased temperature resulted in enhanced ALA production by maintaining the specific rate of synthesis near to the maximal value of 3.6 mg g X −1 h−1, where X* is free fatty acid biomass, and increased the corresponding yield by a factor of up to three.
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  • 5
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The energetics of growth of the fission yeast Schizosaccharomyces pombe was studied in continuous high-cell concentration cultures using a cell-recycle fermentor. Under non-O2-limited conditions, steady-states were obtained at various specific growth rates (partial cell-recycle) with purely oxidative (glucose limitation) or respiro-fermentative (glucose excess) metabolic behaviour. The stoichiometry of biomass synthesis was established from the elemental composition of the cells and measurements of all the specific metabolic rates, i.e. consumption of glucose and O2 and production of CO2, ethanol and other products. The theoretical yield factor for biomass on glucose was YG,X = 0.85 C-mol·C-mol−1 and maintenance requirements were negligible. Assuming a constant coupling between energy generation and biomass formation for both respirative and respiro-fermentative breakdown of glucose, the biomass yield from ATP (YATP) and the efficiency of oxidative phosphorylation (P/O ratio) could be determined as 9.8 g biomass·mol ATP and 1.28 mol ATP·atom of O2, respectively.
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  • 6
    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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  • 7
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Batch cultures of Medicago sativa cells have been carried out in the dark under aerobic conditions using lactose as the sole carbon source. The stoichiometric analysis has been correlated with both the oxygen demand and the cell productivity in an oxygen-limited cultivation. The minimum oxygen transfer has been estimated to be 12.5 h−1, i.e., 0.3 v.v.m; this initial aeration rate led to cell necrosis. Starting with a low oxygen transfer coefficient kL·a and increasing the air flow rate during the course of fermentation gave an exponential growth phase. The maximum specific growth rate was 0.012 h−1 and the growth yield was 0.43 g.d.w./g. of lactose. On the basis of the mass-balance relation the maintenance coefficient and the maximum growth yield have been calculated.
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  • 8
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The production of organic acids has been tested with bacterial flora selected from a municipal sludge digestor. In order to elucidate the basic mechanisms by which glucose is converted to volatile fatty acids, the examination of non-methanogenic bacteria was attempted. Both lactate-producers and lactate-utilizers were found among these bacteria. When mixed isolates were used as the inoculum, the accumulation of lactic acid and its further conversion to propionic and butyric acids was demonstrated at a carbon conversion rate of about 0.75. It is therefore suggested that this metabolic sequence may occur as a normal process in acidogenic fermentation, which is the first step in anaerobic digestion.
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  • 9
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary During batch cultivation of Catharanthus roseus cell suspensions, alkaloids were found in the culture medium after growth had ceased. Resting cell suspensions with high alkaloid content were obtained by transferring the cells to a medium devoid of 2.4 D (2.4 dichlorophenoxy-acetic acid). A production system with continuous feeding was developped to study alkaloid production by these resting cell suspensions.
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  • 10
    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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