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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 17 (1983), S. 281-286 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Candida wickerhamii produced ethanol under aerated and nonaerated conditions when grown on glucose but only under non-aerated conditions when grown on cellobiose. When the yeast was grown on 20 g·l−1 glucose in fermentation flasks, the substrate was completely utilized and 9.2 g·l−1 ethanol was produced. When 100 g·l−1 glucose was used, only 60% of the substrate was consumed and 23.4 g·l−1 ethanol was produced fermentatively whereas 31 g·l−1 ethanol was produced in an aerated fermenter. Ethanol toxicity was confirmed by adding ethanol to the culture. No ethanol was produced at added ethanol concentrations of 24 g·l−1 or higher although growth occurred even in the presence of 74 g·l−1 ethanol. The fermentation of glucose and cellobiose (20 g·l−1) was completed in 24 h and 125 h with specific growth rates of 0.29 and 0.06 h−1 respectively. β-Glucosidase was produced when grown on either glucose or cellobiose but the differential rate of enzyme production was 64 fold higher on cellobiose. Increased aeration stimulated enzyme production. β-Glucosidase was present in the fermentation broth and associated with the cells under non-aerated conditions and almost exclusively cell-associated under aerated conditions.
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  • 2
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary A defined growth medium was determined for the cellobiose fermenting yeast Candida wickerhamii. Biotin and calcium pantothenate were required for growth while thiamine stimulated growth and ethanol production. The optimum temperature and pH for growth and ethanol production were 30°C and between pH 3 and pH 5 respectively. Oxygen availability played an important role in the fermentation of cellobiose and glucose. The optimum oxygen transfer rate for maximum ethanol production from glucose was 1.75 mmol (g dry biomass · h)−1.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 21 (1985), S. 148-153 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Candida wickerhamii growing on cellobiose produced β-glucosidase with high activity against φ-nitrophenyl glucoside (PNPG) but low activity against cellobiose. β-glucosidase production was constitutive, and was repressed by β-glucosides and glucose. β-glucosides containing an aromatic moiety in the aglycon were the best substrates for β-glucosidase indicating that the enzyme is an aryl-β-glucosidase. A β-glucosidase from C. wickerhamii cells was purified by (NH4)2SO4 precipitation, dialysis, ion-exchange chromatography and gel filtration. The purified enzyme was homogeneous as shown by sodium-dodecyl-sulphate polyacrylamide gel electrophoresis and discontinuous gel electrophoresis. The purified enzyme hydrolysed PNPG but not cellobiose. The Km of the enzyme was 0.185 mM. Glucose inhibited the enzyme competitively and the Ki was 7.5 mM. The apparent molecular mass was 97,000. The optimum pH and temperature for enzyme activity were between pH 7 and 7.4 and 40°C respectively. At temperatures of 45°C and greater the enzyme was inactivated. The activation energy of the enzyme was 29.4 kJ · mol-1.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 18 (1983), S. 369-373 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Glucose and cellobiose are the principle sugars released during cellulose hydrolysis. The utilization of mixtures of these sugars (10 g·l−1) by Candiada wickerhamii in batch cultures under aerobic and non-aerated conditions was investigated. Glucose was utilized first followed by cellobiose after a diauxic lag. Ethanol was produced from glucose under both aerobic and non-aerated conditions. Following glucose depletion under aerobic conditions, ethanol (produced during growth on glucose) and cellobiose were utilized simultaneously. Under non-aerated conditions ethanol was produced from cellobiose after the diauxic lag. When the glucose concentration was increased from 2 to 8 g·l−1 in glucose: cellobiose mixtures (total sugar 10 g·l−1), decreases of 66–91% were observed in the specific rates of growth, ethanol production, β-glucosidase production and sugar utilization on cellobiose as well as an increase in the diauxic time lag under aerobic and non-aerated conditions. After depletion of glucose, the viability of C. wickerhamii decreased during cellobiose utilization.
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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 growth and ethanol production by the d-xylose-fermenting yeasts Pichia stipitis and Pachysolen tannophilus under various conditions of aerobiosis responded similarly to the addition of the respiratory inhibitors potassium cyanide (KCN), antimycin A (AA), sodium azide and rotenone. However, the d-glucose-fermenting yeast Saccharomyces cerevisiae differed markedly from these yeasts in response to the inhibitors. In general the growth of the d-xylose-fermenting yeasts was inhibited by the respiratory inhibitors while ethanol production was either stimulated (especially when oxygen was available) or unaffected or inhibited by rotenone or AA or KCN and sodium azide, respectively. However, by exception KCN and AA stimulated ethanol production under aerobic conditions by Pichia stipitis and Pachysolen tannophilus respectively. Stimulatory or inhibitory effects by respiratory inhibitors were less marked in S. cerevisiae. These data suggest that unimpaired mitochondrial function is necessary for growth on d-xylose and optimal d-xylose fermentation. A requirement for membrane generated energy during d-xylose utilisation is indicated by 2,4-dinitrophenol inhibition of growth and fermentation.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 28 (1988), S. 63-68 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The effect of oxygen availability on d-xylose and D-glucose metabolism by Pichia stipitis, Candida shehatae and Pachysolen tannophilus was investigated. Oxygen was not required for fermentation of d-xylose or d-glucose, but stimulated the ethanol production rate from both sugars. Under oxygen-limited conditions, the highest ethanol yield coefficient (Ye/s) of 0.47 was obtained on d-xylose with. P. stipitis, while under similar conditions C. shehatae fermented d-xylose most rapidly with a specific productivity (qpmax) of 0.32 h-1. Both of these yeasts fermented d-xylose better and produced less xylitol than. P. tannophilus. Synthesis of polyols such as xylitol, arabitol, glycerol and ribitol reduced the ethanol yield in some instances and was related to the yeast strain, carbon source and oxygen availability. In general, these yeasts fermented d-glucose more rapidly than d-xylose. By contrast Saccharomyces cerevisiae fermented d-glucose at least three-fold faster under similar conditions.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The uptake of d-{1-13C} xylose, the accumulation of intermediates and the distribution of the label in ethanol in Pichia stipitis under aerobic and anaerobic conditions were investigated by nuclear magnetic resonance spectroscopy. The rate-limiting step of d-xylose metabolism under aerobic conditions appeared to be uptake, whereas under anaerobic conditions it was the conversion of xylitol to xylulose. The yeast showed no preference to either the alpha-or beta-forms of d-xylose. Under anaerobic conditions only {2-13C{ ethanol was detected and this suggests that NADH but not NADPH was used as cofactor in the conversion of xylose to xylitol. d-Xylose is most likely metabolised by the pentose phosphate pathway in this yeast.
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  • 8
    ISSN: 1432-0983
    Keywords: Osmotic stress ; Glycerol ; Glycerol-3-phosphate dehydrogenase ; Glucose repression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Micro-organisms have developed systems to adapt to sudden changes in the environment. Here we describe the response of the yeastSaccharomyces cerevisiae to osmotic stress. A drop in the water activity (aw) of the medium following the addition of NaCl led to an immediate shrinkage of the cells. During the 2 h following the osmotic shock the cells partially restored their cell volume. This process depended on active protein synthesis. During the recovery period the cells accumulated glycerol intracellularly as a compatible solute and very little glycerol was leaking out of the cell. We have investigated in more detail the enzymes of glycerol metabolism and found that only the cytoplasmic glycerol-3-phosphate dehydrogenase was strongly induced. The level of induction was dependent on the yeast strain used and the degree of osmotic stress. The synthesis of cytoplasmic glycerol-3-phosphate dehydrogenase is also regulated by glucose repression. Using mutants defective in glucose repression (hxk2Δ), or derepression (snf1Δ), and with invertase as a marker enzyme, we show that glucose repression and the osmotic-stress response system regulate glycerol-3-phosphate dehydrogenase synthesis independently. We infer that specific control mechanisms sense the osmotic situation of the cell and induce responses such as the production and retention of glycerol.
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  • 9
    ISSN: 1432-072X
    Keywords: d-Xylose fermentation ; Aeration level ; Xylose reductase ; Xylitol dehydrogenase ; Yeast ; Candida shehatae ; Candida tenuis ; Pichia stipitis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between the degree of aerobiosis, xylitol production and the initial two key enzymes of d-xylose metabolism were investigated in the yeasts Pichia stipitis, Candida shehatae and C. tenuis. Anoxic conditions severely curtailed growth and retarded ethanol productivity. This, together with the inverse relationship between xylitol accumulation and aeration level, suggested a degree of redox imbalance. The ratios of NADH- to NADPH-linked xylose reductase were similar in all three yeasts and essentially independent of the degree of aerobiosis, and thus did not correlate with their differing capacities for ethanol production, xylitol accumulation or growth under the different conditions of aerobiosis. Under anoxic conditions the enzyme activity of Pichia stipitis decreased significantly, which possibly contributed to its weaker anoxic fermentation of xylose compared to C. shehatae.
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  • 10
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary When the oxygen supply to an aerobic chemostat culture ofCandida shehatae growing on D-xylose was reduced to oxygen-limited and anoxic conditions, accumulation of ethanol occurred, the specific activity of alcohol dehydrogenase (ADH) increased up to four-fold and the number of ADH isozymes detected increased from one to three. ADH in crude extracts prepared from anoxically-grown cells had a lower affinity for but was more tolerant to ethanol than in extracts prepared from aerobically grown cells. ADH activity appeared to be sufficient for ethanol production byC. shehatae under anoxic conditions.
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