High hydrostatic pressure leads to free radicals accumulation in yeast cells triggering oxidative stress.

Saccharomyces cerevisiae is a unicellular organism that during the fermentative process is exposed to a variable environment; hence, resistance to multiple stress conditions is a desirable trait. The stress caused by high hydrostatic pressure (HHP) in S. cerevisiae resembles the injuries generated by other industrial stresses. In this study, it was confirmed that gene expression pattern in response to HHP displays an oxidative stress response profile which is expanded upon hydrostatic pressure release. Actually, reactive oxygen species (ROS) concentration level increased in yeast cells exposed to HHP treatment and an incubation period at room pressure led to a decrease in intracellular ROS concentration. On the other hand, ethylic, thermic and osmotic stresses did not result in any ROS accumulation in yeast cells. Microarray analysis revealed an upregulation of genes related to methionine metabolism, appearing to be a specific cellular response to HHP, and not related to other stresses, such as heat and osmotic stresses. Next, we investigated whether enhanced oxidative stress tolerance leads to enhanced tolerance to HHP stress. Overexpression of STF2 is known to enhance tolerance to oxidative stress and we show that it also leads to enhanced tolerance to HHP stress.

High hydrostatic pressure activates gene expression that leads to ethanol production enhancement in a Saccharomyces cerevisiae distillery strain.

High hydrostatic pressure (HHP) is a stress that exerts broad effects on microorganisms with characteristics similar to those of common environmental stresses. In this study, we aimed to identify genetic mechanisms that can enhance alcoholic fermentation of wild Saccharomyces cerevisiae isolated from Brazilian spirit fermentation vats. Accordingly, we performed a time course microarray analysis on a S. cerevisiae strain submitted to mild sublethal pressure treatment of 50 MPa for 30 min at room temperature, followed by incubation for 5, 10 and 15 min without pressure treatment. The obtained transcriptional profiles demonstrate the importance of post-pressurisation period on the activation of several genes related to cell recovery and stress tolerance. Based on these results, we over-expressed genes strongly induced by HHP in the same wild yeast strain and identified genes, particularly SYM1, whose over-expression results in enhanced ethanol production and stress tolerance upon fermentation. The present study validates the use of HHP as a biotechnological tool for the fermentative industries.

Influence of cellular fatty acid composition on the response of Saccharomyces cerevisiae to hydrostatic pressure stress.

High hydrostatic pressure (HHP) interferes with cellular membrane structure. The orientation of lipid molecules is changed, especially in the vicinity of proteins, leading to decreased membrane fluidity. Adaptation to HHP requires increased membrane fluidity, often achieved through a rise in the proportion of unsaturated fatty acids. In this work, a desaturase-deficient Saccharomyces cerevisiae mutant strain (OLE1 gene deletion) was grown in media supplemented with fatty acids differing in size and number of unsaturations and submitted to pressure up to 200 MPa for 30 min. Desaturase-deficient yeast supplemented with palmitoleic acid demonstrated increased sensitivity to pressure compared to cells supplemented with oleic acid or a proportionate mixture of both acids. In contrast, yeast cells grown with linoleic and linolenic acids were more piezoresistant than cells treated with oleic acid. Furthermore, growth with palmitoleic acid led to higher levels of lipid peroxidation. Intracellular trehalose during HHP treatment increased cell tolerance to pressure. However, when trehalose remained extracellular cells were sensitised to pressure. Therefore, fatty acid composition and trehalose content might play a role in the protection of the cell membrane from oxidative damage produced by HHP, confirming that alteration in cell membrane fluidity is correlated with pressure resistance in yeast.

Biotechnological properties of distillery and laboratory yeasts in response to industrial stresses.

The stress sensitivity of different wild-type strains was evaluated, as well as the response of cells arrested at different cell cycle positions to high hydrostatic pressure (HPP). HHP was chosen both for its importance in food decontamination and assessment of its suitability as a model for stress in general and understanding the yeast stress response. Studies were conducted with four industrial strains and four laboratory wild-type yeast strains (two haploid and two diploid) that differed in their backgrounds. Fundamental differences were found between the laboratory and industrial populations. Industrial strains were clearly more sensitive to hydrostatic pressure and ethanol stresses than the laboratory strains. However, ethanol production was higher in industrial strains than laboratory strains. Furthermore, no correlation was observed between ploidy and stress resistance. Yeast cells arrested in the G1 phase led to an enhancement in pressure tolerance compared to unarrested, G2 arrested, and S arrested cells. Moreover, cells arrested in the S phase were more sensitive to hydrostatic pressure than cells arrested in the G2 phase. Again, industrial strains were more sensitive than laboratory strains. HHP responses of industrial yeasts correlated well with both ethanol concentration and temperature stress, which suggests that it would be a useful model stress.

High hydrostatic pressure activates transcription factors involved in Saccharomyces cerevisiae stress tolerance.

A number of transcriptional control elements are activated when Saccharomyces cerevisiae cells are submitted to various stress conditions, including high hydrostatic pressure (HHP). Exposure of Saccharomyces cerevisiae cells to HHP results in global transcriptional reprogramming, similar to that observed under other industrial stresses, such as temperature, ethanol and oxidative stresses. Moreover, treatment with a mild hydrostatic pressure renders yeast cells multistress tolerant. In order to identify transcriptional factors involved in coordinating response to high hydrostatic pressure, we performed a time series microarray expression analysis on a wild S. cerevisiae strain exposed to 50 MPa for 30 min followed by recovery at atmospheric pressure (0.1 MPa) for 5, 10 and 15 min. We identified transcription factors and corresponding DNA and RNA motifs targeted in response to hydrostatic pressure. Moreover, we observed that different motif elements are present in the promoters of induced or repressed genes during HHP treatment. Overall, as we have already published, mild HHP treatment to wild yeast cells provides multiple protection mechanisms, and this study suggests that the TFs and motifs identified as responding to HHP may be informative for a wide range of other biotechnological and industrial applications, such as fermentation, that may utilize HHP treatment.

High hydrostatic pressure and the cell membrane: stress response of Saccharomyces cerevisiae.

The brewing and baking yeast Saccharomyces cerevisiae is a useful eukaryotic model of stress response systems whose study could lead to the understanding of stress response mechanisms in other organisms. High hydrostatic pressure (HHP) exerts broad effects upon yeast cells, interfering with cell membranes, cellular architecture, and the processes of polymerization and denaturation of proteins. In this review, we focus on the effect of HHP on the S. cerevisiae cell membrane and describe the main signaling pathways involved in the pressure response.