Because of the exhaustion of fossil fuels and environmental problems such as global warming and acid rain, the utilization of biomass as a resource of renewable, environmentally-friendly energy such like a bio-fuel, has attracted much attention in recent years. In particular, bioethanol produced from biomass, including fast-growing plant species and waste paper, has been suggested as a promising alternative fuel. Due to overcome to this global problem, we attempted the construction of

directed fermentation system from biomass to bioethanol by using cell surface engineered yeast. Several anchored proteins (such like a GPI-anchor, Flo1p [1], and cohesin) were used for displaying of biomass-catalyzed enzymes (amylase, and cellulase). In the case of glucoamylase-displaying yeast cell, glucose was maintained at a very low concentration and, a high ethanol-production rate was achieved. In addition, the glucose concentration in culture medium was usually maintained at a low level, because the recombinant yeast cells metabolize the glucose as soon as glucose was released from soluble starch by the glucoamylase displayed on the cell surface [2,3]. In the

fermentation of the sulfuric acid hydrolysate of wood chips, xylose and cellooligosaccharides were completely fermented after 36 h by the recombinant yeast having a fusion gene of A. aculeatus BGL1 and 3'-half

of ?-agglutinin for its cell-surface display. As a result, about 30 g/l ethanol was produced from 73 g/l total sugar added at the beginning [4-5]. These results demonstrate that the fermentation of the raw starch and lignocellulose hydrolysate could be performed efficiently by the

recombinant Saccharomyces strain with abilities for biomass degradation.

References

1. A. Kondo et al.: Appl. Microbiol. Biotechnol., Vol. 64, 28-40 (2004)

2. H. Shigechi et al.: Appl. Environ. Micobiol., Vol. 70, 5037-5040 (2004)

3. Y. Fujita et al.: Appl. Environ. Micobiol., Vol. 70, 1207-1212 (2004)

4. S. Katahira et al.: Appl. Environ. Micobiol., Vol. 70, 5407-5414 (2004)

5. S. Katahira, et al.: Enzyme Microbial Technol. in press (2008)