Oxygen is required to restore flor strain viability and lipid biosynthesis under fermentative conditions

Abstract

To further elucidate the biosynthesis of lipids in flor strains under fermentative conditions, the transcription levels of the lipid biosynthetic genes ACS1, ACS2, ACC1, OLE1, ERG1, ERG11, ARE1 and ARE2, as well as the lipid composition and cell viability of a flor strain were compared with that of a non-flor strain during hypoxic and aerobic fermentations in the absence of lipid nutrients. While no significant differences in transcription levels or lipid compositions were observed between the two strains when oxygen was not limiting, significant differences were seen during hypoxic fermentation. In this last condition, the flor strain, in spite of higher levels of transcription of hypoxic genes, lost the abilities to desaturate fatty acids and complete ergosterol biosynthesis, and showed a dramatic loss of viability. In contrast, the non-flor strain, which showed lower transcription levels, was able to reach a balanced lipid composition and maintained a higher cell viability. One possible explanation is that the flor strain requires a higher amount of oxygen than the non-flor strain in order to carry out the oxygen-dependent steps of lipid biosynthesis under fermentative conditions.

Transcriptomic Response of Saccharomyces cerevisiae during Fermentation under Oleic Acid and Ergosterol Depletion

“…Considering that higher acetic acid concentrations are indicative of an impaired lipid biosynthesis [25], SJ appeared the adequate medium to evaluate the yeast response to the specific stress induced by lack of lipids. In the chosen conditions the two strains showed a different susceptibility to undergo stuck/sluggish fermentation, in accordance with previous observations [4,15,26]. In particular, EC1118 showed identical fermentation profiles in the two media, while M25 was unable to complete the fermentation in SJ.…”

Effect of oxygen and lipid supplementation on the volatile composition of chemically defined medium and Chardonnay wine fermented with Saccharomyces cerevisiae

“…Since biomass dictates fermentation rate (Varela, Pizarro, & Agosin, 2004) it is likely that a lower biomass yield in the unsupplemented ferments is responsible for the slower fermentation rate observed. Addition of unsaturated lipids and/or oxygen to must directly influences the lipid composition of the yeast cell (Beltran et al, 2006;Zara et al, 2009), which increases membrane unsaturation index and membrane fluidity. Higher unsaturation correlates with tolerance to ethanol stress and might explain the increase in viability (Alexandre, Rousseaux, & Charpentier, 1994;Larue et al, 1980;Mauricio et al, 1991).…”

Sucrose Fermentation by Brazilian Ethanol Production Yeasts in Media Containing Structurally Complex Nitrogen Sources

“…1 and 2, Table I). Recent studies report on the implications in the central carbon metabolism of S. cerevisiae induced by aerobic and anaerobic conditions and address the complexity of the role of oxygen in controlling cellular physiology in yeasts 32,37,38,39 , considering its multiple role in yeast metabolism, such as during the biosynthesis of unsaturated fatty acids, ergosterol, heme group, mitochondrial development and others 37 . It has been reported that an optimized oxygen supply is critical, because too much oxygen could cause yeast degeneration, due to the toxic effect of reactive oxygen species 37 .…”