Studies on the wine spoilage capacity of Brettanomyces/Dekkera spp.

The presence of Brettanomyces/Dekkera in wine during barrel aging is often associated with detrimental organoleptic effects. The mechanisms underlying the capacity of these yeast species to grow and survive in wine with high ethanol levels and low sugar supply were investigated. Ethanol was used by Brettanomyces bruxellensis ISA 1791 and Dekkera anomala IGC 5153 as the sole carbon and energy source, the growth of the yeasts being dependent on the concentration of alcohol in the culture media. When specific growth rates of both yeasts were plotted against ethanol concentration, at high substrate levels there was a decline in the specific growth rate rather than an asymptotic approach to mu(max) according to the Monod-based Bungay equation. Moreover, these yeasts exhibited greater capacity to grow at high ethanol concentrations than Saccharomyces cerevisiae IGC 4072. When glucose was used as the sole carbon and energy source, the growth of B. bruxellensis showed lower sensitivity to ethanol toxic effects than S. cerevisiae. In transport assays carried out with B. bruxellensis grown with glucose as the carbon source, the yeast expressed activity for two transport systems for the monosaccharide: facilitated diffusion, specific for glucose and fructose, and H+-dependent transport, specific for glucose and galactose and subject to glucose repression. The activity of both transport systems was inhibited noncompetitively by ethanol according to exponential inhibition kinetics, but 12% alcohol reduced sugar transport only by 60%. Findings help explain the ability of Brettanomyces/Dekkera spp. to grow and survive under the severe environmental conditions of wine.