Utilization and transport of acetic acid in Dekkera anomala and their implications on the survival of the yeast in acidic environments

The yeast Dekkera anomala IGC 5153 exhibited a restricted ability to use we ak acids as the only carbon and energy sources. Of the monocarboxylic, dica rboxylic, and tricarboxylic acids tested, only acetic acid was used in such a way. The cells were able to grow at acetic acid concentrations of 0.1 to 3% (vol/vol) over a pH range of 3.5 to 5.5, and the specific growth rates decreased exponentially with the increase of the undissociated acetic acid concentration in the culture medium. Transport assays carried out in cells that exhibited higher specific growth rates showed the presence of an aceta te-proton symport associated with a simple diffusion component of the undis sociated acetic acid, the weight of the latter increasing with the undissoc iated acid concentration in the culture media. The acetate carrier was shar ed by propionic, formic, and sorbic acids and was inducible and repressed b y glucose and concentrations of undissociated acetic acid in the culture me dium above 0.3% (vol/vol). In undissociated acetic acid repression conditio ns, the lowest values for the yeast specific growth rates were obtained, an d the simple diffusion of the undissociated acid was the only mechanism inv olved in the acetic acid uptake by the cells. The results will be discussed in terms of the high tolerance of D. anomala to the acidic stress conditio ns present in wine.