Role of Transcriptional Factor Znf1 in Isobutanol Tolerance in Saccharomyces cerevisiae

Branched-chain alcohols are attractive advanced biofuels. However, their toxicity to the host
is still the main problem that limits the yield of product. We investigated the growth of a single
deletion strains of S. cerevisiae lacking the pentose phosphate pathway gene (namely the zwf1Δ,
gnd1Δ, tkl1Δ, tal1Δ or rpe1Δ) on YPD media plates containing different concentrations of
isobutanol. We also determined the role of transcriptional factor Znf1 in isobutanol tolerance in
yeast S. cerevisiae. Phenotypic analysis revealed the most hypertolerant strain, overexpression
ZNF1 in 1.5%, 2%, or 2.2 % of isobutanol compared to the wild-type and the znf1Δ. Moreover, the
zwf1Δ and the gnd1Δ strains displayed the hypersensitive to isobutanol as found in the tkl1Δ or
rpe1Δ strains. We also measured cell density in liquid YPD media containing 1.5% isobutanol. The
growth of znf1Δ was found to be 80% when normalized to the wild-type strain. However, the
overexpression ZNF1 strain demonstrated enhance tolerance up to 150 % in the presence of 1.5 %
isobutanol, compared to the wild-type strain. Additionally, downregulation of the ZWF1 gene
encoding the enzyme which catalyzes NADPH generation by 2-folds was observed in the znf1Δ
strain. This indicates the role of Znf1 in cofactor imbalance, which may help yeast cells to survive
under isobutanol stress by supplying energy in the form of NADPH. Finally, the decreased
expression levels of valine biosynthesis genes, including ILV3 and ARO10, were found (2-folds) in
the znf1Δ strain, which demonstrates its regulation of valine biosynthesis genes in the pathway of
isobutanol production.