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

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.