Simultaneously improving xylose fermentation and tolerance to lignocellulosic inhibitors through evolutionary engineering of recombinant Saccharomyces cerevisiae harbouring xylose isomerase
Date
2014-05
Authors
Smith, Justin
Van Rensburg, Eugene
Gorgens, Johann F.
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: Yeasts tolerant to toxic inhibitors from steam-pretreated lignocellulose with xylose co-fermentation
capability represent an appealing approach for 2nd generation ethanol production. Whereas rational engineering,
mutagenesis and evolutionary engineering are established techniques for either improved xylose utilisation or
enhancing yeast tolerance, this report focuses on the simultaneous enhancement of these attributes through
mutagenesis and evolutionary engineering of Saccharomyces cerevisiae harbouring xylose isomerase in anoxic
chemostat culture using non-detoxified pretreatment liquor from triticale straw.
Results: Following ethyl methanesulfonate (EMS) mutagenesis, Saccharomyces cerevisiae strain D5A+ (ATCC
200062 strain platform), harbouring the xylose isomerase (XI) gene for pentose co-fermentation was grown in
anoxic chemostat culture for 100 generations at a dilution rate of 0.10 h−1 in a medium consisting of 60% (v/v)
non-detoxified hydrolysate liquor from steam-pretreated triticale straw, supplemented with 20 g/L xylose as carbon
source. In semi-aerobic batch cultures in the same medium, the isolated strain D5A+H exhibited a slightly lower
maximum specific growth rate (μmax = 0.12 ± 0.01 h−1) than strain TMB3400, with no ethanol production observed
by the latter strain. Strain D5A+H also exhibited a shorter lag phase (4 h vs. 30 h) and complete removal of HMF,
furfural and acetic acid from the fermentation broth within 24 h, reaching an ethanol concentration of 1.54 g/L at a
yield (Yp/s) of 0.06 g/g xylose and a specific productivity of 2.08 g/gh. Evolutionary engineering profoundly affected
the yeast metabolism, given that parental strain D5A+ exhibited an oxidative metabolism on xylose prior to strain
development.
Conclusions: Physiological adaptations confirm improvements in the resistance to and conversion of inhibitors
from pretreatment liquor with simultaneous enhancement of xylose to ethanol fermentation. These data support
the sequential application of random mutagenesis followed by continuous culture under simultaneous selective
pressure from inhibitors and xylose as primary carbon source.
Description
Publication of this article was funded by the Stellenbosch University Open Access Fund.
The original publication is available at http://www.biomedcentral.com/1472-6750/14/41
Please site as follows:
Smith, J., Van Rensburg, E., & Gorgens, J. F. 2014. Simultaneously improving xylose fermentation and tolerance to lignocellulosic inhibitors through evolutionary engineering of recombinant Saccharomyces cerevisiae harbouring xylose isomerase. BMC Biotechnology, 14:41, doi:10.1186/1472-6750-14-41.
The original publication is available at http://www.biomedcentral.com/1472-6750/14/41
Please site as follows:
Smith, J., Van Rensburg, E., & Gorgens, J. F. 2014. Simultaneously improving xylose fermentation and tolerance to lignocellulosic inhibitors through evolutionary engineering of recombinant Saccharomyces cerevisiae harbouring xylose isomerase. BMC Biotechnology, 14:41, doi:10.1186/1472-6750-14-41.
Keywords
Saccharomyces cerevisiae, Yeast hardening, Evolutionary engineering
Citation
Smith, J., Van Rensburg, E., & Gorgens, J. F. 2014. Simultaneously improving xylose fermentation and tolerance to lignocellulosic inhibitors through evolutionary engineering of recombinant Saccharomyces cerevisiae harbouring xylose isomerase. BMC Biotechnology, 14:41, doi:10.1186/1472-6750-14-41.