Bioethanol Production from Cellulosic Materials by Cell Surface Engineered Yeast Strains
Akihiko Kondo, Yasuya Fujita, Satoshi Katahira, and Hideki Fukuda. Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai-cho, Nada, kobe, 657-8501, Japan
Display of novel enzymes on the yeast cell surface is very powerful method to develop the efficient whole cell biocatalysts, because the diffusion problem of substrate and product is circumvented. In addition, the displayed enzymes are regarded as a kind of self-immobilized enzyme on the cell surfaces. In this study, we have developed the novel methods to display enzymes using cell wall anchoring proteins alpha-agglutinin. To show their applicability to the productions of biofuels and chemicals from biomass, the ethanol production from cellulosic materials was investigated by using yeast cells displaying cellulolytic enzymes. Due to the display of these enzymes, cellulosic materials were sequentially hydrolyzed to glucose on the yeast cell surface, immediately utilized and converted to ethanol by intracellular enzymes. The yield in terms of grams of ethanol produced per grams of carbohydrate utilized was over 0.45, which corresponds to over 89% of theoretical yield. These results demonstrate that a combination of cell surface displayed enzymes and intracellular metabolic system is a very effective approach to develop cells with novel catalytic and metabolic abilities for industrial applications.