Directed Evolution and Genomic Analysis of Novel Yeast Species for More Efficient Biomass Conversion

Introduction We propose to develop novel, adaptively evolved, hybrid yeast strains having phenotypes that enhance the efficiency of industrial-scale biomass conversion. Specifically, we propose to develop heatand ethanol-tolerant yeast that convert both xylose and glucose to ethanol, studying key aspects of their functional and systems biology as they evolve. Initially, we will increase the amount of standing genetic variation upon which natural selection can act, by hybridizing species in the Saccharomyces sensu stricto group. Thereafter we will direct the evolution of rare, viable F2 hybrid progeny in chemostats, selecting for industrially desirable traits. Through successive rounds of crossbreeding and selection, we will be able to recombine these traits, without recourse to genetic modifications other than those wrought by natural selection. We will use DNA microarrays to assay both genome architectural and gene expression changes that occur during adaptive evolution. These studies will reveal the contribution of specific changes in DNA content and gene expression patterns to xylose fermentation and enhanced ethanoland thermo-tolerance. These insights can be used to direct future efforts aimed at achieving still greater conversion efficiencies under industrially relevant conditions. Achieving this aim is essential to the national strategic goal of transforming a geology-based economy, supported by non-renewable resources, to a biology-based economy, supported by renewable resources that include forest and agricultural residuals. Life cycle analyses indicate that such an economy, centered on the concept of the integrated biorefinery, would have the added advantage of zero net greenhouse gas emission. The specific goals of this project are: