Octanoic (C8) and decanoic (C10) acids are produced in hypoxic conditions by the yeast Saccharomyces cerevisiae as by-products of its metabolism and are considered fermentation inhibitors in the presence of ethanol at acidic pH. This study aims to broaden our understanding of the physiological limits between toxicity and ester production in yeast cells. To this end, the non-inhibitory concentration (NIC) and maximum inhibitory concentration (MIC) values were first established for C8 and C10 at physiological pH (5.8) without ethanol. The results showed that when these acids were added to culture medium at these values, they tended to accumulate in different cellular fractions of the yeast. While C8 was almost entirely located in the cell wall fraction, C10 was found in the endocellular fraction. Cell fatty acid detoxification was also different; while the esterification of fatty acids was more efficient in the case of C10, the peroxisome was activated regardless of which fatty acid was added. Furthermore, the study of the Pdr12 and Tpo1 transporters that evolved during the detoxification process revealed that C8 was mostly expelled by the Pdr12 carrier, which was related to higher β-oxidative damage in the presence of endocellular C10. C10 is more toxic at lower concentrations than C8. Although they are produced by yeast, the resulting intracellular medium-chain fatty acids (MCFAs) caused a level of toxicity which promoted cell death. However, MCFAs are involved in the production of beverage flavours.
In the present study, we analysed metabolite features during the dehydration-rehydration process for different yeast species genetically closely related to S. cerevisiae, in order to determine whether metabolites might play a role in cell viability. We ranked the species S. cerevisiae, S. paradoxus, S. kudriavzevii, L. kluyveri, N. castellii, S. mikatae, S. bayanus, and S. servazzii according to their viability rate after the dehydrationrehydration process, and showed that desiccation tolerance across the species did not correlate with the intracellular content of trehalose or glycogen. Cell lipid composition was also investigated during this process, to see whether the content of triacylglycerols and phosphatidylcholine showed significant variations across the species. The increase of phosphatidylcholine level increase in both S. paradoxus and S. bayanus cells grown in supplemented media enhanced both their cell viability after stress imposition and lipid storage.
The yeast Saccharomyces cerevisiae is able to overcome cell dehydration; cell metabolic activity is arrested during this period but restarts after rehydration. The yeast genes encoding hydrophilin proteins were characterised to determine their roles in the dehydration-resistant phenotype, and STF2p was found to be a hydrophilin that is essential for survival after the desiccation-rehydration process. Deletion of STF2 promotes the production of reactive oxygen species and apoptotic cell death during stress conditions, whereas the overexpression of STF2, whose gene product localises to the cytoplasm, results in a reduction in ROS production upon oxidative stress as the result of the antioxidant capacity of the STF2p protein.
A simple gas chromatography‐mass spectrometry (GC‐MS) method has been developed for the determination of neutral lipids in yeast. This method was compared to the conventional thin‐layer chromatography (TLC) method used in our laboratory. The new method enabled the measurement of molecular species of diacylglycerols, triacylglycerols, and sterol esters (SE). With a classic lipid extraction, samples can be injected directly into the GC‐MS without any previous derivatization procedure. However, the main characteristic of this new method is its versatility because GC parameters can be modified based on the biological samples analyzed: volume and injection modes, derivatization of samples, etc. In order to validate the method, yeast lipid extracts from two distinct culture growth conditions were compared, the first in presence of oxygen and the second in its absence. Although the lipid profile of both yeast samples is qualitatively similar, the use of the GC‐MS method rather than the TLC method enables the identification of a sterol, neoergosterol, in yeast cells grown in absence of oxygen. Moreover, this method enables phospholipid detection in samples but their identification is difficult.
GC‐MS total ion chromatogram of full chromatogram of yeast lipid extracts (positive values represent cells grown in the presence of oxygen while negative values represent cells grown without oxygen). STs: sterols; PLs: phospholipids; DAGs: diglycerides; SEs: sterol esters; TAGs: triglycerides.
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