Stress‐tolerance of baker's‐yeast (Saccharomyces cerevisiae) cells: stress‐protective molecules and genes involved in stress tolerance

Abstract

During the fermentation of dough and the production of baker's yeast (Saccharomyces cerevisiae), cells are exposed to numerous environmental stresses (baking-associated stresses) such as freeze-thaw, high sugar concentrations, air-drying and oxidative stresses. Cellular macromolecules, including proteins, nucleic acids and membranes, are seriously damaged under stress conditions, leading to the inhibition of cell growth, cell viability and fermentation. To avoid lethal damage, yeast cells need to acquire a variety of stress-tolerant mechanisms, for example the induction of stress proteins, the accumulation of stress protectants, changes in membrane composition and repression of translation, and by regulating the corresponding gene expression via stress-triggered signal-transduction pathways. Trehalose and proline are considered to be critical stress protectants, as is glycerol. It is known that these molecules are effective for providing protection against various types of environmental stresses. Modifications of the metabolic pathways of trehalose and proline by self-cloning methods have significantly increased tolerance to baking-associated stresses. To clarify which genes are required for stress tolerance, both a comprehensive phenomics analysis and a functional genomics analysis were carried out under stress conditions that simulated those occurring during the commercial baking process. These analyses indicated that many genes are involved in stress tolerance in yeast. In particular, it was suggested that vacuolar H+-ATPase plays important roles in yeast cells under stress conditions.

Bread Dough and Baker's Yeast: An Uplifting Synergy

“…Yeast cells can accumulate glycerol and trehalose when osmotic pressure is sensed (Hirasawa and others 2006;Shima and Takagi 2009). Indeed, high-sucrosetolerant (HS) yeast strains show a high expression of proteins required for the production of glycerol and trehalose when sucrose concentrations reach 5 to 40%.…”

“…Trehalose and proline are considered to be critical stress protectants, as is glycerol. These molecules are effective for providing protection against various types of environmental stresses (Shima and Takagi 2009). The accumulation of proline increased cell viability in osmotic stress conditions and enhanced fermentation ability in sweet or salted dough (Takagi and others 1997;Poole and others 2009;Sasano and others 2012b).…”

“…To avoid lethal injury, baker's yeast cells need to acquire osmotolerance by the induction of stress protein expression, the accumulation of stress protectants, and changes in their membrane composition (Shima and Takagi 2009). Yeast cells can accumulate glycerol and trehalose when osmotic pressure is sensed (Hirasawa and others 2006;Shima and Takagi 2009).…”

Environmental Stresses to Which Yeast Cells Are Exposed During Bioethanol Production from Biomass

“…In general, microorganisms show some ability to adapt to environmental stresses. Yeast cells also need to acquire a variety of stress-adaptation mechanisms, such as the induction of stress proteins, the accumulation of stress protectants, changes in membrane composition, and the repression of translation, and by regulating the corresponding gene expression via stresstriggered signal transduction pathways (Shima and Takagi 2009 ;Attfi eld 1997 ). Under severe stress conditions, however, the fermentation ability of yeast is rather limited.…”

“…As occurs in the production of traditional liquor, such as sake, and with bread fermentation (Shima and Takagi 2009 ), yeast cells are exposed to numerous environmental stresses including chemical, temperature, acid, and osmolality stresses ( Fig. 6.1 ).…”