• 作者： 張勝祺; 鐘順昌; Sigenori Yoshikawa
• 作者服務機構： 國立陽明醫學院生化科; Mycology Department; American Type Culture Collection; Central Laboratory of Yamazaki Bakin Co.; LTD.
• 中文摘要： 從市面產品收集之23種麵包酵母菌分離出27菌株，研究顯示此27菌株皆為敏感性菌株，會被 Killer 菌株殺死，因此利用原生質融合技術來構築麵包酵母菌具有 Killer Plasmid。經由選擇性培養基及 Killer 活性之篩選，得到融合菌株，經由研究顯示於固定化作用及醱酵作用之表現型，皆與麵包酵母菌相同，而於 Killer 活性之表現型則與提供 Killer Plasmid菌株之 Killer 表現型相同，除外，此些融合菌株證明皆含有 Killer Plasmid，由此得知此些融合菌株為麵包酵母菌具有Killer Plasmid。 當 Killer Plasmid 從 Killer 酵母菌轉移到麵包酵母菌後，能在麵包酵母菌細胞中穩定地存在，即使保存於-70°C液態氮或冷凍乾燥條件下4個月。另外從溫度及pH值對 Killer Plasmid 影響之研究，顯示所構築麵包酵母菌具有 Killer Plasmid之菌株，可被應用於工業上避免被不要之酵母菌污染。
• 英文摘要： Killer yeasts which carry double strand RNA plasmid kill sensitive strains of the same species andother yeasts by secreting protein toxins. Twenty-seven strains of Saccharomyces cerevisiae isolated from 23commercial bakers’yeast samples were found to be killer sensitive. Therefore, a killer strain of bakers’yeast was constructued by using the protoplast fusion technique with a commercial bakers’strain (ATCC58511) and a kar-I mutant (ATCC 44075) of the killer plasmid donor which is defective for nuclear fusion.The killer bakers’yeast constructed showed the same pattern in fermentation and assimilation as that ofthe bakers’yeast and expressed the same killer phenotype as that of the killer strain. The double-strand RNA plasmid which confers the killer phenotype in the bakers’yeast has beenstably maintained for generations when grown at 24°C to 30°C or when stored in the freeze-dried state orin the vapor phase of liquid nitrogen at -70°C. The optimum pH for the expression of killer toxin was4.0-4.5. The killer toxin was completely denatured at pH 5.5. In general, the industrial production of bakers’yeast is carried out at 30°C with a pH value of 4.2-5.2. Doughs are mixed with bakers’yeast and enter the fermentation room at a temperature of 25-30°C.During fermentation the maximum gassing activity is attained between pH values of 4 to 6. Therefore,the constructed killer bakers’yeast (ATCC 60003) may be used in breadmaking to prevent contaminationfrom other undesirable yeasts.
• 中文關鍵字： bakers' yeast; killer plasmid; protoplast fusion
• 英文關鍵字： --