Č. Novotný

Effect of clomiphene on the content of sterols and fatty acids inSaccharomyces cerevisiae

During cultivation ofSaccharomyces cerevisiae clomiphene regulates both quantitative and qualitative production of sterols and fatty acids as identified by gas chromatography and mass speetrometry. The content of sterols decreases to 75 %, the production of fatty acids is comparable with that in the control. The occurrence of sterols increases; sterols with methyl group in position 4, without double bond in position 22 and with double bond in position 24(25) or 24(28) predominate. Among fatty acids shorter saturated and monoene acids are primarily produced, 2-hydroxy acids practically disappeared.

Ethanol-Induced Death and Lipid Composition of Saccharomyces cerevisiae: A Comparative Study of the Role of Sterols

Ethanol tolerance of fourSaccharomyces cerevisiae strains characterized by different amounts of Δ5,7-sterols was tested. The individual tolerances did not correlate with the strains sterol levels. The highly and medium-accumulating strains exhibited the highest and lowest ethanol tolerances, respectively.

Effect of ammonium ions on †5,7-sterol synthesis inSaccharomyces cerevisiae

The effect of ammonium concentration in the medium on †5,7-sterol synthesis was examined. Higher concentrations of this nitrogen source in the medium decreased sterol synthesis and accumulation during growth. An intermittent supply with ammonium resulted in a proportional synthesis of †5,7-sterols and biomass. The carbon to nitrogen molar ratio of ≧ 40 allowed the maximum accumulation of †5,7-sterols with our strain of baker’s yeast.

Kinetics of Δ5,7-sterol accumulation during growth ofSaccharomyces cerevisiae

Saccharomyces cerevisiae accumulates Δ5,7-sterols up to 4 mg per g biomass. The differential rate of sterol synthesis continually increases during growth, its value only being decreased at sterol levels higher than 30 mg per g biomass. The specific rate of sterol synthesis reaches a broad maximum during the growth phase. The gradual sterol accumulation pattern is dominant in cultures growing both on fermentable and nonfermentable carbon sources and is modulated by glucose repression. Limited feeding with sucrose has a significantly greater negative impact on sterol accumulation than feeding with ethanol as a carbon source.

Effect of growth rate on ethanol tolerance of Saccharomyces cerevisiae

AbstractΔ5,7Saccharomyces cerevisiae cells growing in chemostat at a specific growth rate of 0.075/h exhibited higher ethanol tolerance measured as ethanol-induced death and anaerobic growth inhibition than the cells growing at 0.2/h, the difference being dependent on the carbon-to-nitrogen molar proportion in the medium. The observed difference in sensitivity to ethanol of anaerobic growth between the slowly and rapidly-growing cells was completely reversed as a result of a block in sterol synthesis causing a negligible synthesis of Δ5,7. Two physiological parameters, budding frequency and membrane composition, evidently affected ethanol tolerance. Differences between the Δ5,7 and deficient strains documented a profound effect of the quality of the sterol present on the physiological state of the cell.

Sterol composition of a δ5,7-sterol-rich strain ofSaccharomyces cerevisiae during batch growth

Sterol composition was examined during batch growth on complex media containing ethanol, molasses or glucose as the carbon source. The molasses-grown cells exhibited a balanced sterol composition throughout growth, maintaining the proportion of eigosterol to 24:28-dehydroergosterol equal to 1.4. The negative effect of glucose on sterol synthesis manifested itself by decreasing the accumulation of 24:28-dehydroergosterol and total sterols but not of ergosterol. Using ethanol as the sole carbon source, a large amount of 24:28-dehydroergosterol accumulated, partly at the expense of other sterols. The gradual addition of nitrogon source during growth significantly decreased the accumulation of ergosterol, 24:28-dehydroergosterol and of total sterols. A general scheme of regulation of sterol synthesis in baker’s yeast is presented.

Effect of cyclic adenosine-3′,5′-monophosphate on the simultaneous synthesis of β-galactosidase and tryptophanase inEscherichia coli

When inducing simultaneously β-galactosidase and tryptophanase in a batch culture either the synthesis of tryptophanase or of both enzymes is decreased due to an insufficient cAMP concentration. The addition of this nucleotide can overcome this decrease. In a continuous culture both enzymes are synthesized at the maximum rate, as the amount of cAMP produced during carbon limitation of growth is probably sufficient for the simultaneous synthesis of both enzymes. In the β-galactosidase hyperproduction mutant cultivated continuously the level of β-galactosidase markedly decreases when tryptophanase is simultaneously induced. Also this decrease is caused by cAMP insufficiency and can be overcome by increasing its concentration. cAMP is thus an important regulatory factor of both enzymes and becomes a limiting factor in their simultaneous synthesis; a competition for this regulatory compound apparently occurs and probably also a different mutual affinity of the regulatory complex with the promoter site of the enzyme opérons is involved.

Linear growth in microbial cultures limited by accumulated substrate

SummaryThe “linear” growth phase in cultures limited by intracellular (conservative) substrate is represented by a flat exponential curve. Within the range of experimental errors, the presented model fits well the data from both batch and continuous cultures ofEscherichia coli, whose growth is limited in that way.

Inducible synthesis of β-galactosidase inKluyveromyces fragilis

Lactose,d-galactose, andl-arabinose induce the synthesis of β-galactosidase inKluyveromyces fragilis. Lactose is the best inducer with a maximum effect at 1.4 mm. The induced synthesis of the enzyme in glycerol grown stationary phase cells is triggered within 30 min of inducer addition, the full induction being achieved within subsequent 30–40 min.

Instability of the tetrathionate respiratory chain ofCitrobacter freundii

The formate—tetrathionate reductase redox pathway ofCitrobacter freundii is associated with the cytoplasmic membrane fraction. A high concentration of phosphate in the buffer used for cell disintegration assists in the preparing of membrane particles capable of efficient tetrathionate respiration. A part of this effect at least may be attributed to the high ionic strength of the buffer.