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Title: Morphology and molecular physiology of zygosaccharomyces spoilage yeasts
Author: Nunn, Christopher D.
ISNI:       0000 0004 2750 6378
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2004
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Spoilage is a major problem for the food industry ultimately resulting in economic loss. Among the most prominent spoilage yeasts are members belonging to the Zygosaccharomyces genus. This research focuses on differences in organic acid resistance and the physiological basis of these differences between Zygosaccharomyces bailii, Zygosaccharomyces kombuchaensis and Saccharomyces cerevisiae. Z. bailii , Z kombuchaensis and S. cerevisiae differ in resistance to short, medium and longer chain organic acids. Organic acid resistance was shown to be effected by alterations to growth conditions. S. cerevisiae was the most sensitive to organic acids followed by Z. kombuchaensis. Z. bailii was overall the most resistant to organic acids. Organic acid inhibition was shown to increase with increasing chain length. Electron microscopy was used to determine the effects of organic acids on yeast cell structure. Evidence is presented for short, medium and longer chain organic acids differing in their mode of inhibition. The cell wall was highlighted as differing between Z. bailii, Z. kombuchaensis and S. cerevisiae and as having a role in yeast organic acid resistance. Protoplast fusion was successfully applied to Z. bailii and Z. kombuchaensis with S. cerevisiae to study the role of mitochondria in yeast organic acid resistance. Differences in sensitivity to ethidium bromide and petite forming capabilities were demonstrated. Hybrids were characterized in terms of morphology, physiology and organic acid resistance. The ability of Z. bailii, Z. kombuchaensis and S. cerevisiae to form pseudohyphae in the presence of isoamyl alcohol was assessed. Isoamyl alcohol was shown to induce an osmotic stress with a role for the high osmolality glycerol pathway being demonstrated. Z. bailii was shown to contain a subgroup based on differences in organic acid resistance, morphology, physiology and molecular composition. This is the first time that a subgroup with increased sensitivity to organic acids has been reported for Z. bailii.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available