Xylose fermentation efficiency of industrial Saccharomyces cerevisiae yeast with separate or combined xylose reductase/xylitol dehydrogenase and xylose isomerase pathways

Joana T Cunha; Pedro O Soares; Aloia Romaní; Johan M Thevelein; Lucília Domingues

doi:10.1186/s13068-019-1360-8

Xylose fermentation efficiency of industrial Saccharomyces cerevisiae yeast with separate or combined xylose reductase/xylitol dehydrogenase and xylose isomerase pathways

Biotechnol Biofuels. 2019 Jan 28:12:20. doi: 10.1186/s13068-019-1360-8. eCollection 2019.

Authors

Joana T Cunha¹, Pedro O Soares¹, Aloia Romaní¹, Johan M Thevelein^{2

3}, Lucília Domingues¹

Affiliations

¹ 1CEB-Centre of Biological Engineering, University of Minho, 4710-057 Braga, Portugal.
² 2Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Department of Biology, KU Leuven, Kasteelpark Arenberg 31, 3001 Leuven-Heverlee, Flanders Belgium.
³ 3Center for Microbiology, VIB, Kasteelpark Arenberg 31, 3001 Leuven-Heverlee, Flanders Belgium.

Abstract

Background: Xylose isomerase (XI) and xylose reductase/xylitol dehydrogenase (XR/XDH) pathways have been extensively used to confer xylose assimilation capacity to Saccharomyces cerevisiae and tackle one of the major bottlenecks in the attainment of economically viable lignocellulosic ethanol production. Nevertheless, there is a lack of studies comparing the efficiency of those pathways both separately and combined. In this work, the XI and/or XR/XDH pathways were introduced into two robust industrial S. cerevisiae strains, evaluated in synthetic media and corn cob hemicellulosic hydrolysate and the results were correlated with the differential enzyme activities found in the xylose-pathway engineered strains.

Results: The sole expression of XI was found to increase the fermentative capacity of both strains in synthetic media at 30 °C and 40 °C: decreasing xylitol accumulation and improving xylose consumption and ethanol production. Similar results were observed in fermentations of detoxified hydrolysate. However, in the presence of lignocellulosic-derived inhibitors, a positive synergistic effect resulted from the expression of both XI and XR/XDH, possibly caused by a cofactor equilibrium between the XDH and furan detoxifying enzymes, increasing the ethanol yield by more than 38%.

Conclusions: This study clearly shows an advantage of using the XI from Clostridium phytofermentans to attain high ethanol productivities and yields from xylose. Furthermore, and for the first time, the simultaneous utilization of XR/XDH and XI pathways was compared to the single expression of XR/XDH or XI and was found to improve ethanol production from non-detoxified hemicellulosic hydrolysates. These results extend the knowledge regarding S. cerevisiae xylose assimilation metabolism and pave the way for the construction of more efficient strains for use in lignocellulosic industrial processes.

Keywords: Hemicellulosic ethanol; Industrial yeast; Lignocellulosic hydrolysates; Xylose consumption; Xylose isomerase; Xylose reductase/xylitol dehydrogenase.