Affiliation:
1. Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, New York 14456
Abstract
ABSTRACT
In this investigation, we examined the effects of different unsaturated fatty acid compositions of
Saccharomyces cerevisiae
on the growth-inhibiting effects of ethanol. The unsaturated fatty acid (UFA) composition of
S. cerevisiae
is relatively simple, consisting almost exclusively of the mono-UFAs palmitoleic acid (Δ
9
Z-C
16:1
) and oleic acid (Δ
9
Z-C
18:1
), with the former predominating. Both UFAs are formed in
S. cerevisiae
by the oxygen- and NADH-dependent desaturation of palmitic acid (C
16:0
) and stearic acid (C
18:0
), respectively, catalyzed by a single integral membrane desaturase encoded by the
OLE1
gene. We systematically altered the UFA composition of yeast cells in a uniform genetic background (i) by genetic complementation of a desaturase-deficient
ole1
knockout strain with cDNA expression constructs encoding insect desaturases with distinct regioselectivities (i.e., Δ
9
and Δ
11
) and substrate chain-length preferences (i.e., C
16:0
and C
18:0
); and, (ii) by supplementation of the same strain with synthetic mono-UFAs. Both experimental approaches demonstrated that oleic acid is the most efficacious UFA in overcoming the toxic effects of ethanol in growing yeast cells. Furthermore, the only other UFA tested that conferred a nominal degree of ethanol tolerance is
cis
-vaccenic acid (Δ
11
Z-C
18:1
), whereas neither Δ
11
Z-C
16:1
nor palmitoleic acid (Δ
9
Z-C
16:1
) conferred any ethanol tolerance. We also showed that the most ethanol-tolerant transformant, which expresses the insect desaturase
Tni
NPVE, produces twice as much oleic acid as palmitoleic acid in the absence of ethanol and undergoes a fourfold increase in the ratio of oleic acid to palmitoleic acid in response to exposure to 5% ethanol. These findings are consistent with the hypothesis that ethanol tolerance in yeast results from incorporation of oleic acid into lipid membranes, effecting a compensatory decrease in membrane fluidity that counteracts the fluidizing effects of ethanol.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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