Effect of Fermentation Conditions on the Flocculation of Recombinant Saccharomyces cerevisiae Capable of Co-fermenting Glucose and Xylose |
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Authors: | Akinori Matsushika Hiroyo Morikawa Tetsuya Goshima Tamotsu Hoshino |
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Institution: | 1. Biomass Refinery Research Center (BRRC), National Institute of Advanced Industrial Science and Technology (AIST), 3-11-32 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-0046, Japan 2. Graduate School of Life Science, Hokkaido University, N10W8 Kita-ku, Sapporo, Hokkaido, 060-0810, Japan
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Abstract: | Flocculation is a desirable property in industrial yeasts and is particularly important in the fuel ethanol industry because it provides a simple and cost-free way to separate yeast cells from fermentation products. In the present study, the effect of pH and lignocellulose-derived sugars on yeast flocculation was investigated using a flocculent Saccharomyces cerevisiae, MA-R4, which has been recombinantly engineered to simultaneously co-ferment glucose and xylose to ethanol with high productivity. The flocculation level of MA-R4 dramatically decreased at pH values below 3.0 during co-fermentation of glucose and xylose. Sedimentation and microscopic observation revealed that flocculation was induced in MA-R4 when it fermented glucose, a glucose/xylose mixture, or mannose, whereas attempts to ferment xylose, galactose, and arabinose led to the loss of flocculation. MA-R4 fermented xylose and galactose more slowly than glucose and mannose. Therefore, the various flocculation behaviors shown by MA-R4 should be useful in the control of ethanol fermentation processes. |
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