Background: The major carbohydrate components of lignocellulosic biomass are cellulose
and hemicelluloses. Saccharomyces cerevisiae cannot efficiently utilize xylose derived upon
the hydrolysis of hemicelluloses. Although engineering the yeast with xylose metabolic pathway
has been intensively studied, challenges are still ahead for developing robust strains for lignocellulosic
Objective: The main objective of this study was to reveal the role of the MIG1 mutant isolated from
the self-flocculating S. cerevisiae SPSC01 in xylose utilization, glucose repression and ethanol
fermentation by S. cerevisiae.
Methods: The MIG1 mutant was amplified from S. cerevisiae SPSC01 by PCR and MIG1-
overexpression-cassette was transformed into S. cerevisiae S288c and xylose-metabolizing strain
YB-2625-T through homologous recombination. Yeast growth was measured by colony assay on
plates with or without xylose supplementation. Then xylose utilization and ethanol production were
further evaluated through flask fermentation when mixed sugars of glucose and xylose at 3:1 and
2:1, respectively, were supplied. Fermentation products were detected by HPLC, and activities of
xylose reductase (XR), xylitol dehydrogenase (XDH) and xylulokinase (XK) were also measured.
The transcription of genes regulated by the expression of the MIG1 mutant was analyzed by RTqPCR.
Evolutionary relationship of various MIG1s was developed by gene sequencing and sequence
Results: No difference was observed for S288c growing with xylose when it was engineered with
the overexpression or deletion of its native MIG1, but its growth was enhanced when overexpressing
the MIG1 mutant from SPSC01. The submerged culture of YB-2625-T MIG1-SPSC engineered
with xylose-metabolic pathway and the MIG1 mutant indicated that xylitol accumulation was decreased,
and consequently, more biomass was accumulated. Furthermore, improved activities of the
key enzymes such as XR, XDH and XK were detected in YB-2625-T MIG1-SPSC. Evolutionary
analysis of MIG1s amplified from S. cerevisiae strains commonly used for ethanol production revealed
a close relationship of SPSC01 and YB-2625.
Conclusion: Our results demonstrated the effect of the overexpression of the MIG1 mutant from
SPSC01 on xylose utilization of S. cerevisiae. This study could be an alternative strategy for engineering
S. cerevisiae with improved xylose utilization.