Freer S N, Skory C D
Fermentation Biochemistry Research Unit, U.S. Department of Agriculture (USDA), Peoria, IL 61604, USA.
Can J Microbiol. 1996 May;42(5):431-6. doi: 10.1139/m96-059.
The fermentation of cellobiose is a rare trait among yeasts. Of the 308 yeast species that utilize cellobiose aerobically, only 12 species ferment it, and only 2 species, Candida molischiana and Candida wickerhamii, also ferment cellodextrins. Candida molischiana produced beta-glucosidase activity on all carbon sources tested, except glucose, mannose, and fructose. When these sugars were added to cultures growing on cellobiose, the synthesis of beta-glucosidase ceased. However, the total amount of enzyme activity remained constant, indicating that the C. molischiana beta-glucosidase is catabolite repressed and not catabolite inactivated. When grown in medium initially containing glucose plus xylose, cellobiose, maltose, mannitol, or glucitol, C. molischiana preferentially utilized glucose and produced little beta-glucosidase activity until glucose was nearly depleted from the medium. When grown in medium containing cellobiose plus either fructose or mannose, the yeast preferentially utilized the monosaccharides and produced little beta-glucosidase activity. Candida molischiana produced beta-glucosidase and co-utilized cellobiose and xylose, maltose, or trehalose. Glucose and fructose, mannose, or trehalose were co-utilized; however, no beta-glucosidase activity was detected. Thus, the order of substrate preference groups appeared to be (glucose, trehalose, fructose, mannose) > (cellobiose, maltose, xylose) > (mannitol, glucitol).
纤维二糖发酵在酵母中是一种罕见的特性。在308种能有氧利用纤维二糖的酵母物种中，只有12种能发酵它，并且只有2种，即摩氏假丝酵母和威克汉姆假丝酵母，也能发酵纤维糊精。摩氏假丝酵母在除葡萄糖、甘露糖和果糖之外的所有测试碳源上都产生β-葡萄糖苷酶活性。当将这些糖添加到在纤维二糖上生长的培养物中时，β-葡萄糖苷酶的合成停止。然而，酶活性的总量保持不变，这表明摩氏假丝酵母β-葡萄糖苷酶受到分解代谢物阻遏而非分解代谢物失活。当在最初含有葡萄糖加木糖、纤维二糖、麦芽糖、甘露醇或山梨醇的培养基中生长时，摩氏假丝酵母优先利用葡萄糖，并且在葡萄糖几乎从培养基中耗尽之前几乎不产生β-葡萄糖苷酶活性。当在含有纤维二糖加果糖或甘露糖的培养基中生长时，该酵母优先利用单糖并且几乎不产生β-葡萄糖苷酶活性。摩氏假丝酵母产生β-葡萄糖苷酶并共同利用纤维二糖和木糖、麦芽糖或海藻糖。葡萄糖与果糖、甘露糖或海藻糖共同利用；然而，未检测到β-葡萄糖苷酶活性。因此，底物偏好顺序组似乎是（葡萄糖、海藻糖、果糖、甘露糖）>（纤维二糖、麦芽糖、木糖）>（甘露醇、山梨醇）。
