title: Quantitative analysis of the modes of growth inhibition by weak organic acids in Saccharomyces cerevisiae.
abstract: Weak organic acids are naturally occurring compounds that are commercially used as preservatives in the food and beverage industries. They extend the shelf life of food products by inhibiting microbial growth. There are a number of theories that explain the antifungal properties of these weak acids, but the exact mechanism is still unknown. We set out to quantitatively determine the contributions of various mechanisms of antifungal activity of these weak acids, as well as the mechanisms that yeast uses to counteract their effects. We analyzed the effects of four weak organic acids differing in lipophilicity (sorbic, benzoic, propionic, and acetic acids) on growth and intracellular pH (pH(i)) in Saccharomyces cerevisiae. Although lipophilicity of the acids correlated with the rate of acidification of the cytosol, our data confirmed that not initial acidification, but rather the cell's ability to restore pH(i), was a determinant for growth inhibition. This pH(i) recovery in turn depended on the nature of the organic anion. We identified long-term acidification as the major cause of growth inhibition under acetic acid stress. Restoration of pH(i), and consequently growth rate, in the presence of this weak acid required the full activity of the plasma membrane ATPase Pma1p. Surprisingly, the proposed anion export pump Pdr12p was shown to play an important role in the ability of yeast cells to restore the pH(i) upon lipophilic (sorbic and benzoic) acid stress, probably through a charge interaction of anion and proton transport.
authors.affiliation: Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences, Netherlands Institute for Systems Biology, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Azmat
authors.initials: A
authors.lastname: Ullah
authors.forename: Rick
authors.initials: R
authors.lastname: Orij
authors.forename: Stanley
authors.initials: S
authors.lastname: Brul
authors.forename: Gertien J
authors.initials: GJ
authors.lastname: Smits
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000935:Antifungal Agents / Q000378:metabolism*; D002264:Carboxylic Acids / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry; D005520:Food Preservatives / Q000378:metabolism*; D006131:Growth Inhibitors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000254:growth & development*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D000935:Antifungal Agents; D002264:Carboxylic Acids; D005520:Food Preservatives; D006131:Growth Inhibitors; C472673:Pdr12 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C092477:PMA1 protein, S cerevisiae; D006180:Proton-Translocating ATPases