Molecular Basis of the Response to Stress of Oenococcus oeni to Inhibitory Compounds Produced by Yeasts During Wine Fermentation

Oenococcus oeni is the main lactic acid bacterium responsible for malolactic fermentation (MLF) during winemaking, a critical step for obtaining high-quality wines. However, the harsh wine environment, characterized by low pH, ethanol, sulfur dioxide, and inhibitory yeast metabolites, can compromise bacterial growth and MLF performance. To investigate the mechanisms underlying wine stress tolerance, O. oeni CRL 1947 was grown in unfermented and fermented grape juice media and analyzed using a proteomic (two-dimensional electrophoresis) and RT-qPCR. A total of 38 proteins displayed significant differential expression under all conditions, with 23 up-regulated and 15 down-regulated. One protein spot (fructokinase) was exclusively detected in fermented medium, whereas aspartate carbamoyltransferase was completely inhibited. Proteins related to carbohydrate, lipid, nucleotide, and amino acid metabolism, as well as stress-response chaperones and peptidases, were over-expressed in fermented grape juice medium. In contrast, enzymes involved in lipid biosynthesis, glycolysis, amino acid metabolism, hydrolase, and dehydrogenase activities were down-regulated. Differential expression of genes associated with malic acid and citrate metabolism as well as in stress response was also observed. These findings provide further insights into the molecular adaptations of O. oeni to wine-stressful conditions and support the selection of the best adapted starter cultures for efficient MLF during winemaking.