Novel stress responses facilitate Saccharomyces cerevisiae growth in the presence of the monocarboxylate preservatives

Abstract

Certain yeasts are relatively resistant to the small number of monocarboxylic acids allowed in food preservation, with the result that these preservatives often have to be used in high concentrations in order to prevent spoilage. When grown at slightly acid pH, Saccharomyces cerevisiae acquires elevated resistance to these acids by means of discrete stress responses. Acquisition of resistance to acetic acid involves loss of Fps1p, the aquaglyceroporin of the plasma membrane that facilitates the passive diffusional entry of this acid into cells. Acetic acid stress transiently activates Hog1p mitogen-activated protein kinase, which then directly phosphorylates Fps1p in order to target this channel for endocytosis and degradation in the vacuole. Other carboxylate preservatives (propionate, sorbate or benzoate) are too large to traverse the Fps1p pore. Instead, being more lipophilic than acetic acid, they enter cells mainly by a process of non-facilitated diffusion across the plasma membrane. Once inside the cell, these acids activate War1p, a transcription factor that induces the gene for the Pdr12p plasma membrane ATP-binding cassette transporter. Pdr12p lowers the intracellular levels of propionate, sorbate or benzoate by catalysing the active efflux of the preservative anion from the cell. Still other mechanisms of weak acid resistance are found in Zygosaccharomyces, including a capacity for the oxidative degradation of sorbic and benzoic acids conferred by a mitochondrial monooxygenase, a system absent in S. cerevisiae.

Quantitative Analysis of the Modes of Growth Inhibition by Weak Organic Acids in Saccharomyces cerevisiae

“…A number of theories have been presented to explain the antifungal properties of weak acids, including acidification of the cytoplasm, anion accumulation, membrane perturbation, and ATP depletion (4,29,50). To what extent these various mechanisms contribute to the antifungal activities of weak acids is still unresolved.…”

Acetate but not propionate induces oxidative stress in bakers’ yeastSaccharomyces cerevisiae

“…7,33 In general, baker's yeast cells are known to be relatively resistant to monocarboxylic WOAs. 14,16 At least three different mechanisms are supposed to be responsible for that:…”

“…16,37,38 Yeast can extrude acid anions through the anion efflux pump Pdr12p, which has been found to mediate resistance to both AA and PA. 18 However, later works by the same research group reported that acetate did not induce expression of PDR12 gene, while PA did. 17,39 It was believed that expression of Pdr12p is controlled by the sole War1p transcriptional factor.…”

“…Recently, Mollapour et al 16 suggested that reduction of endogenous oxidative stress is one of the major advantages of Pdr12p. Our study shows that CP level in the yeast lacking War1p is significantly higher compared to the parental strain (Fig.…”

“…[13][14][15] On the other hand, baker's yeast is shown to be relatively resistant to monocarboxylic WOAs. 14,16 One of the most important mechanisms protecting yeast against acid stress is prevention of intracellular accumulation of acid anions to high, potentially toxic levels. Adenosine-5 ′ -triphosphate (ATP) binding cassette Pdr12p appears to be acting as an efflux pump for WOA anions.…”