Adaptive Response and Tolerance to Acetic Acid in Saccharomyces cerevisiae and Zygosaccharomyces bailii: A Physiological Genomics Perspective

Abstract

Acetic acid is an important microbial growth inhibitor in the food industry; it is used as a preservative in foods and beverages and is produced during normal yeast metabolism in biotechnological processes. Acetic acid is also a major inhibitory compound present in lignocellulosic hydrolysates affecting the use of this promising carbon source for sustainable bioprocesses. Although the molecular mechanisms underlying Saccharomyces cerevisiae response and adaptation to acetic acid have been studied for years, only recently they have been examined in more detail in Zygosaccharomyces bailii. However, due to its remarkable tolerance to acetic acid and other weak acids this yeast species is a major threat in the spoilage of acidic foods and beverages and considered as an interesting alternative cell factory in Biotechnology. This review paper emphasizes genome-wide strategies that are providing global insights into the molecular targets, signaling pathways and mechanisms behind S. cerevisiae and Z. bailii tolerance to acetic acid, and extends this information to other weak acids whenever relevant. Such comprehensive perspective and the knowledge gathered in these two yeast species allowed the identification of candidate molecular targets, either for the design of effective strategies to overcome yeast spoilage in acidic foods and beverages, or for the rational genome engineering to construct more robust industrial strains. Examples of successful applications are provided.

Keywords: Saccharomyces cerevisiae; Zygosaccharomyces bailii; acetic acid adaptive response; acetic acid tolerance; physiological genomics; weak acid food preservatives.

FIGURE 1

Functional genomics-based approaches explored to obtain mechanistic insights into the adaptive response and tolerance to sublethal and lethal concentrations of acetic acid in S. cerevisiae and Z. bailii.

FIGURE 2

Schematic model for the adaptive response of S. cerevisiae to acetic acid-induced stress as detailed in the text. pH_ext, external pH; pH_i, intracellular pH.

FIGURE 3

Schematic model for the adaptive response of Z. bailii to acetic acid-induced stress. Details are provided in the text. pH_ext, external pH; pH_i, intracellular pH; TCA, tricarboxylic acid.

FIGURE 4

Proposed model for TORC2-Ypk1 dependent activation of the sphingolipid biosynthetic pathway in acetic acid-stressed S. cerevisiae cells. TORC2, Target of Rapamycin (TOR) Complex 2; FA-CoA, fatty acyl-CoA; LCB, long chain base.

FIGURE 5

Schematic model of the mechanisms proposed to regulate Haa1 activity in S. cerevisiae, in response to lactic and acetic acid-induced stress. The description of the proposed events is detailed in the text. pH_ext, external pH; pH_i, intracellular pH.