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  • 1
    ISSN: 0749-503X
    Keywords: yeast ; Candida utilis ; alcoholic fermentation ; Kluyver effect ; oxygen limitation ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The facultatively fermentative yeast Candida utilis exhibits the Kluyver effect for maltose: this disaccharide is respired and assimilated but, in contrast to glucose, it cannot be fermented. To study the mechanism of the Kluyver effect, metabolic responses of C. utilis to a transition from aerobic, sugar-limited growth to oxygen-limited conditions were studied in chemostat cultures. Unexpectedly, the initial response of maltose-grown cultures to oxygen limitation was very similar to that of glucose-grown cultures. In both cases, alcoholic fermentation occurred after a lag phase of 1 h, during which glycerol, pyruvate and D-lactate were the main fermentation products. After ca. 10 h the behaviour of the maltose- and glucose-grown cultures diverged: ethanol disappeared from the maltose-grown cultures, whereas fermentation continued in steady-state, oxygen-limited cultures grown on glucose. The disappearance of alcoholic fermentation in oxygen-limited chemostat cultures growing on maltose was not due to a repression of the synthesis of pyruvate decarboxylase and alcohol dehydrogenase. The results demonstrate that the Kluyver effect for maltose in C. utilis does not reflect an intrinsic inability of this yeast to ferment maltose, but is caused by a regulatory phenomenon that affects a key enzyme in maltose metabolism, probably the maltose carrier. The observed kinetics indicate that this regulation occurs at the level of enzyme synthesis rather than via modification of existing enzyme activity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3592
    Keywords: Kluyveromyces ; Candida utilis ; Kluyver effect ; chemostat ; biomass ; whey ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many facultatively fermentative yeast species exhibit a “Kluyver effect”: even under oxygen-limited growth conditions, certain disaccharides that support aerobic, respiratory growth are not fermented, even though the component monosaccharides are good fermentation substrates. This article investigates the applicability of this phenomenon for high-cell-density cultivation of yeasts. In glucose-grown batch cultures of Candida utilis CBS 621, the onset of oxygen limitation led to alcoholic fermentation and, consequently, a decrease of the biomass yield on sugar. In maltose-grown cultures, alcoholic fermentation did not occur and oxygen-limited growth resulted in high biomass concentrations (90 g dry weight L-1 from 200 g L-1 maltose monohydrate in a simple batch fermentation). It was subsequently investigated whether this principle could also be applied to Kluyveromyces species exhibiting a Kluyver effect for lactose. In oxygen-limited, glucose-grown chemostat cultures of K. wickerhamii CBS 2745, high ethanol concentrations and low biomass yields were observed. Conversely, ethanol was absent and biomass yields on sugar were high in oxygen-limited chemostat cultures grown on lactose. Batch cultures of K. wickerhamii grown on lactose exhibited the same growth characteristics as the maltose-grown C. utilis cultures: absence of ethanol formation and high biomass yields. Within the species K. marxianus, the occurrence of a Kluyver effect for lactose is known to be strain dependent. Thus, K. marxianus CBS 7894 could be grown to high biomass densities in lactose-grown batch cultures, whereas strain CBS 5795 produced ethanol after the onset of oxygen limitation and, consequently, yielded low amounts of biomass. Because the use of yeast strains exhibiting a Kluyver effect obviates the need for controlled substrate-feeding strategies to avoid oxygen limitation, such strains should be excellently suited for the production of biomass and growth-related products from low-cost disaccharide-containing feedstocks. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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