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Document Type |
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Thesis |
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Document Title |
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Genetic and Molecular Studies on some Killer Yeasts دراسات وراثية وجزيئية على بعض الخمائر القاتلة |
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Subject |
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Faculty of Science |
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Document Language |
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Arabic |
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Abstract |
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Twenty-nine yeast strains belonging to two various genera were tested for their ability to kill each other. Candida krusei strain 15, Candida lipolytica strain 17, Candia tropicales strain 21 and Candida utilis strain 25, Saccharomyces cerevisiae strain 26, Saccharomyces cerevisiae strain 28, Saccharomyces cerevisiae strain 29, were the most killer strains. Candida krusei strain 14, Saccharomyces cerevisiae strain 27 and Candida tropicalis strain 20 were the most sensitive strains to these killers. The under-investigation killer toxins were precipitated by ammonium sulphate and ethanol, suggesting that they are proteins in nature. Unlike most of the reported toxins these killer toxins showed high thermostability at different temperatures up to 37°C and pH stability between pH 4.6 and 8 for 48 hours. Killer toxin of Saccharomyces cerevisiae strain 28 had the most thermostability and pH stability. Results of different curing experiments and separation of dsRNA revealed that Saccharomyces cerevisiae strain 28 killer toxin is encoded by M dsRNA virus-like particles, while the killer toxins of Candida utilis strain 25 and Saccharomyces cerevisiae strain 26 might be chromosomally encoded. Four spontaneous resistant colonies of the sensitive cerevisiae Saccharomyces strain 27 were isolated from the zone of inhibition around the streak of killer Saccharomyces cerevisiae strain 28. Interestingly, two out of the four isolates were killers and harboring both L-A and M dsRNA plasmids, the others were nonkillers harboring only L-A dsRNA plasmid. The suggestions of virus transmission from the killer strain to the sensitive strain were examined. The three mentioned killer strains were tested for their antibacterial and antifungal activities against two bacterial species and five pathogenic fungal species, respectively. Therefore, the use of the three killer toxins to control unwanted bacteria yeasts and fungi could be expanded beyond applications in foods and feeds. They could be used as prophylactics for the treatment of human animal and plant bacterial and fungal disease.
Key words: Killer yeasts, Killer toxins, dsRNA, dsDNA, Electrophoresis. |
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Supervisor |
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Prof. Sabah Mahmoud Husan |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1441 AH
2020 AD |
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Added Date |
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Wednesday, June 3, 2020 |
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Researchers
| سوزان نوري التركي | Alturki, Suzan Nouri | Researcher | Doctorate | |
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