S56: Development of microbial cell factories for biofuel production from biomass by conslidated bioprocessing

One of the key technologies for the development of biorefineries is cell surface engineering, which is a powerful tool for functionalizing many organisms. Using the technology, various kinds of functional proteins can be expressed on the cell surface without loss of cell activity. The display of cellulolytic enzymes on the surface of Saccharomyces cerevisiae has accomplished direct ethanol production from cellulosic biomass. Moreover, the display of hemicellulase on the surface of S. cerevisiae that has a xylose-assimilating pathway has enabled ethanol production from hemicellulosic materials. Furthermore, reutilization of the cell-surface engineered yeast has an advantage in the reduction of enzyme cost, which enables reuse of enzymes on the cell surface by collecting the cells. Thus, cell surface engineering is a promising technology for the development of a consolidated bioprocess by integrating enzyme production, saccharification and fermentation. For the efficient ethanol production from lignocellulosic materials with microbes, the improvement of both microbial fermentation ability and tolerance to inhibitors is required. Specifically, lignocellulosic hydrolysates contain high concentrations of inhibitors that negatively affect metabolism and ethanol yields. To circumvent these difficulties, robust S. cerevisiae strains that efficiently ferment mixtures of hexose and pentose sugars in the presence of various chemical contexts should be constructed through metabolic engineering approaches. A combination of a cell-surface displayed enzyme system and an intracellular metabolic engineering system is a very effective approach for developing cells with improved fermentation ability for industrial applications. The technology (synthetic bioengineering) will open up new applications of cell factories to industrially important processes.