Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Bioethanol is the most common renewable fuel today. During pretreatment processes for cellulosic biomass, furan-derivatives such as furfural and 5-hydroxymethylfurfural (HMF) are known to decrease the growth of Saccharomyces cerevisiae and hence reduce ethanol productivity significantly. Removal of furfural and HMF in a growth medium by biological or physico-chemical methods is a key factor for obtaining a high fermentation performance. In this study, a genome-wide library of S. cerevisiae was constructed to identify the furan-detoxifying genes. The chromosomal DNA of S. cerevisiae was cut by sonication and the DNA fragments were ligated with plasmid pRS424. The transformants with the resulting plasmids were spread onto the basal medium containing 20 g/L glucose, and 2 g/L furfural or HMF. The transformant colonies growing faster than the control were chosen and the genes in the recombinant strains were identified. Among several gene fragments, the open reading frames of the ROG1, PEP4, SNF1, KIP2, SKO1, RSP5, ROD1 and TRP1 genes were present in the plasmids. Batch fermentation of recombinant S. cerevisiae overexpressing ROG1, PEP4, or TRP1 resulted in a 31% increase in final dry cell mass and a 26% improvement in ethanol productivity compared with the control cultured in the presence of 2 g/L furfural. Consequently, tolerant properties of S. cerevisiae against furan-derived inhibitors were improved by overexpression of the genes discovered by the genome-wide screening.