title: Enhanced xylose fermentation and ethanol production by engineered Saccharomyces cerevisiae strain.
abstract: We have recently demonstrated that heterologous expression of a bacterial xylose isomerase gene (xylA) of Burkholderia cenocepacia enabled a laboratorial Saccharomyces cerevisiae strain to ferment xylose anaerobically, without xylitol accumulation. However, the recombinant yeast fermented xylose slowly. In this study, an evolutionary engineering strategy was applied to improve xylose fermentation by the xylA-expressing yeast strain, which involved sequential batch cultivation on xylose. The resulting yeast strain co-fermented glucose and xylose rapidly and almost simultaneously, exhibiting improved ethanol production and productivity. It was also observed that when cells were grown in a medium containing higher glucose concentrations before being transferred to fermentation medium, higher rates of xylose consumption and ethanol production were obtained, demonstrating that xylose utilization was not regulated by catabolic repression. Results obtained by qPCR demonstrate that the efficiency in xylose fermentation showed by the evolved strain is associated, to the increase in the expression of genes HXT2 and TAL1, which code for a low-affinity hexose transporter and transaldolase, respectively. The ethanol productivity obtained after the introduction of only one genetic modification and the submission to a one-stage process of evolutionary engineering was equivalent to those of strains submitted to extensive metabolic and evolutionary engineering, providing solid basis for future applications of this strategy in industrial strains.
authors: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Leonardo de Figueiredo
authors: Lde F
authors: Vilela
authors: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Verônica Parente Gomes
authors: VP
authors: de Araujo
authors: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Raquel de Sousa
authors: Rde S
authors: Paredes
authors: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Elba Pinto da Silva
authors: EP
authors: Bon
authors: Department of Cellular Biology, Institute of Biology, University of Brasília, Brasília, DF Brazil.
authors: Fernando Araripe Gonçalves
authors: FA
authors: Torres
authors: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Bianca Cruz
authors: BC
authors: Neves
authors: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Elis Cristina Araújo
authors: EC
authors: Eleutherio
keywords: Ethanol; Evolutionary engineering; Saccharomyces cerevisiae; TAL1; Xylose; Xylose isomerase