Stivers, Peter J.. Adaptation and regulation of fatty acid composition in candida albicans in response to environmental conditions. Retrieved from https://doi.org/doi:10.7282/T3XD110D
DescriptionCandida albicans is a commensal fungus that grows
in the mammalian gut at a constant temperature of
37oC. Like most fungi, Candida albicans membranes
contain mono-‐and polyunsaturated fatty acids that
are formed by Δ9, Δ12, and Δ15 fatty acid desaturase
enzymes. Studies of other ectothermic fungi have shown
that desaturases are highly regulated with respect to growth temperatures and the availability of exogenous
nutrient fatty acids. Experiments were performed to
assess whether the lipid composition and fatty acid
desaturases of Candida are regulated under similar
conditions. Candida was found to adapt to temperatures
ranging from 15oC to 37oC, however, at 15oC an unusual 12-‐hour biphasic lag phase was observed before cells entered logarithmic growth. These
experiments showed that cellular fatty acyl composition
was dynamic and varied with both the growth phase and
the growth temperature. Growth at lower temperatures
in the 37oC-‐20oC range resulted in higher levels of
double bonds in membrane lipids, which is consistent
with induced levels of desaturase activities seen in
ectothermic fungi as they adapt to low temperatures.
Unexpectedly, the fatty acyl double bond content in
20oC cells was found to be higher than that at 15oC.
Analysis of the relative mRNA levels for Δ9, Δ12, and
Δ15 desaturases showed a correlation with the respective fatty acyl compositions found at each
temperature. Candida was found to incorporate exogenous polyunsaturated fatty acids from the culture
medium at 30oC and α-‐linolenic acid and γ-‐linolenic
acid accumulated to high levels in cellular lipids, resulting in repressed levels of the endogenous unsaturated species. Arachidonic acid accumulated
in cellular lipids at lower levels under the same conditions, but also produced marked reductions in endogenous 18:1. Analysis of mRNAs from the 30oC
supplemented cells showed that all three fatty acids repressed the Δ9 and Δ15 desaturase mRNA levels while inducing Δ12 desaturase gene expression. In
experiments to test the effects of unsaturated fatty acids
on the ability of Candida to adapt to low temperatures
all three polyunsaturated acids were found to incorporate into lipids at high levels in cells grown at 15oC. This supplementation, however, produced no change in the extent of the lag phase and growth rate of
Candida at 15oC. Under these conditions, all three
exogenous fatty acids were found to repress both Δ9 and Δ12 desaturase mRNA levels.