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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.   Electronic supplementary material  The online version of this article (doi:10.1186/s13568-015-0102-y) contains supplementary material, which is available to authorized users.

Enhanced xylose fermentation and ethanol production by engineered Saccharomyces cerevisiae strain