Bulk Segregant Analysis of CBS1502 lineage GSY2694

Creating Saccharomyces yeasts capable of efficient fermentation of pentoses such as xylose remains a key challenge in the production of ethanol from lignocellulosic biomass. Metabolic engineering of industrial Saccharomyces cerevisiae strains has yielded xylose-fermenting strains, but these strains have not yet achieved industrial viability due largely to xylose fermentation being prohibitively slower than that of glucose. Recently, it has been shown that naturally occurring xylose-utilizing Saccharomyces species exist. Uncovering the genetic architecture of such strains will shed further light on xylose metabolism, suggesting additional engineering approaches, and may even suggest that their remains potential for development of xylose-fermenting yeasts that are not genetically-modified. We previously identified a hybrid yeast strain with the ability to grow on xylose as the sole carbon source. Genetic characterization of this strain using bulk segregant analysis in conjunction with high-throughput sequencing revealed that its growth in xylose is governed by at least four genetic loci. One of the loci maps to a known xylose-pathway gene, a novel allele of the aldo-keto reductase gene GRE3, and a second locus maps to an allele of APJ1, a gene not previously not connected to xylose metabolism. We have not yet determined the causal alleles for the other two loci. Our work demonstrates the power of sequencing applied to bulk segregant analysis in a non genetically-tractable hybrid strain that contains a complex, polygenic trait, and it identifies new avenues for metabolic engineering as well as construction of non-genetically modified xylose-fermenting strains.