Strain-dependent tolerance to acetic acid in Dekkera bruxellensis

Dekkera bruxellensis—a yeast species associated with wine and beer production—has recently received attention because of its ability to compete with Saccharomyces cerevisiae in distilleries producing fuel ethanol, and due to its resistance to high ethanol and acid levels. The tolerance to acetic acid in 29 strains of D. bruxellensis was investigated by screening growth at different concentrations up to 120 mM at pH 4.5. Different metabolic responses were exhibited in three strains (CBS 98, CBS 2499 and CBS 4482) that were analysed by their FTIR-metabolomic fingerprint. Physiological studies showed that the presence of acetic acid significantly affected their growth, causing a different reduction in growth rate, glucose consumption and ethanol production rates, as well as biomass and ethanol yields. The examined strains were unable to metabolise acetic acid in the presence of glucose, probably due to a glucose repression mechanism on the acetyl-CoA syntethase activity. Interestingly, the cells continued to produce acetic acid as byproduct of their fermentative metabolism. We also showed that the HOG MAP kinase pathway was not activated by phosphorylation upon exposure of the cells to acetic acid.