Skip to main content
ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Bioenergy Research » Research » Publications at this Location » Publication #264746
Title: New genotypes of industrial yeast Saccharomyces cerevisiae engineered with YXI and heterologous xylose transporters improve xylose utilization and ethanol production

Author
item Moon, Jaewoong
item Liu, Zonglin
item MA, MENGGEN - New Mexico State University
item Slininger, Patricia - Pat
item Weber, Scott

Submitted to: Biocatalysis and Agricultural Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2013
Publication Date: 3/26/2013
Citation: Moon, J., Liu, Z., Ma, M., Slininger, P.J., Weber, S.A. 2013. New genotypes of industrial yeast Saccharomyces cerevisiae engineered with YXI and heterologous xylose transporters improve xylose utilization and ethanol production. Biocatalysis and Agricultural Biotechnology. 2:247-254.

Interpretive Summary: Recombinant Saccharomyces cerevisiae strains for lignocellulose-to-ethanol conversion applications utilize xylose poorly, especially when present in mixtures with other sugars like glucose. A major barrier is in the lack of an efficient system for xylose uptake and utilization. However, little is known about xylose transport systems in yeast. This research cloned and characterized six xylose transporter genes from a natural xylose utilizing yeast Scheffersomyces (Pichia) stipitis for the first time and demonstrated their enhanced xylose utilization capability when coupled in a strain with a synthesized yeast xylose isomerase. Our transgenic S. cerevisiae strains with the characterized xylose transporter genes were able to increase intracellular xylose accumulation in yeast and competitively utilize xylose in mixed sugar, glucose-xylose fermentations. Incorporation of xylose transporter genes in recombinant S. cerevisiae significantly improved yeast growth rate and ethanol production rate. Results of this study provide new knowledge of xylose transport genes for yeast strain development and bring the research and development efforts of xylose utilization by S. cerevisiae to a new phase. Outcomes of this research will guide continued efforts for more desirable strain design and development for economical lignocellulosic ethanol production.

Technical Abstract: Recombinant strains of the yeast Saccharomyces cerevisiae show a diauxic response and inefficient xylose conversion when mixed sugars are present in fermentations. To date, no ideal yeast is available for efficient lignocellulose-to-ethanol conversion using divergent biomass sugars including both pentoses and hexoses. Inefficient xylose transport is considered a major barrier for effective xylose uptake and utilization. In this study, we cloned and characterized 6 putative xylose transporter genes XUT4, XUT5, XUT6, XUT7, RGT2, and SUT4, from Scheffersomyces (Pichia) stipitis and expressed these genes in an industrial-based S. cerevisiae. The tolerant transgenic host strain Y-50049-YXI contains an in vitro synthesized yeast xylose isomerase by chromosomal integration. Expression of xylose transporter genes in Y-50049-YXI significantly improved xylose uptake and utilization and enabled the yeast to grow on xylose as sole carbon source. The highest volumetric consumption rate of 0.535 g h**-1 was achieved by XUT7 and highest specific growth rate of 1.4 h**-1 by XUT4, a more than 7 and 20 times increase, respectively. During microaerophilic co-fermentation on a glucose-xylose substrate, all xylose transporter gene-containing strains showed competitive xylose utilization in the presence of glucose with minimal diauxic lag. The highest levels of ethanol conversion were observed for strain Y-50049-YXI-RGT2, Y-50049-YXI-XUT7, and Y-50049-YXI-SUT4 at 16 to 18 g l**-1 on medium containing 25 g l**-1 each of D-glucose and D-xylose—a yield range of 64-72% of that theoretically possible. While the functional yeast xylose isomerase is necessary for xylose utilization, the addition of xylose transporter genes from S. stipitis significantly improved xylose-to-ethanol productivity.