Abstract
Xylose is the second most abundant sugar in lignocellulosic materials and can be converted to ethanol by recombinant Saccharomyces cerevisiae yeast strains expressing heterologous genes involved in xylose assimilation pathways. Recent research demonstrated that disruption of the alkaline phosphatase gene, PHO13, enhances ethanol production from xylose by a strain expressing the xylose reductase (XR) and xylitol dehydrogenase (XDH) genes; however, the yield of ethanol is poor. In this study, PHO13 was disrupted in a recombinant strain harboring multiple copies of the xylose isomerase (XI) gene derived from Orpinomyces sp., coupled with overexpression of the endogenous xylulokinase (XK) gene and disruption of GRE3, which encodes aldose reductase. The resulting YΔGP/XK/XI strain consumed 2.08 g/L/h of xylose and produced 0.88 g/L/h of volumetric ethanol, for an 86.8 % theoretical ethanol yield, and only YΔGP/XK/XI demonstrated increase in cell concentration. Transcriptome analysis indicated that expression of genes involved in the pentose phosphate pathway (GND1, SOL3, TAL1, RKI1, and TKL1) and TCA cycle and respiratory chain (NDE1, ACO1, ACO2, SDH2, IDH1, IDH2, ATP7, ATP19, SDH4, SDH3, CMC2, and ATP15) was upregulated in the YΔGP/XK/XI strain. And the expression levels of 125 cell cycle genes were changed by deletion of PHO13.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-015-0175-7) contains supplementary material, which is available to authorized users.
Highlights
Bioethanol is widely viewed as a potential new energy source and alternative to fossil fuels
GRE3, which converts xylose to xylitol (Johansson et al 2001), was deleted
Previous studies reported that the rate of xylose isomerase (XI)-catalyzed conversion of xylose to xylulose is very low in recombinant S. cerevisiae strains
Summary
Bioethanol is widely viewed as a potential new energy source and alternative to fossil fuels. Lignocellulosic materials, which represents an abundant, inexpensive, and renewable resource, are of great interest as a feedstock for bioethanol production. Saccharomyces cerevisiae is an ideal host for bioethanol production due to its high stress tolerance, high ethanol production capacity, and ease of gene manipulation. S. cerevisiae cannot inherently assimilate xylose, the second most abundant sugar in lignocellulosic biomass (Mosier et al 2005). Xylose-assimilating yeast strains have been constructed through genetic engineering to exploit two different heterologous xylose-utilization pathways. The oxidoreductase pathway involves the conversion of xylose to xylitol by xylose reductase (XR) and the conversion of xylitol to Overexpression of downstream metabolic genes such as XKS1 and genes involved in the pentose phosphate
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