| Summary: | <i>Oenococcus oeni</i> is the main agent of malolactic fermentation in wine. This fermentation takes place after alcoholic fermentation, in a low nutrient medium where ethanol and other inhibitor compounds are present. In addition, some yeast-derived compounds such as mannoproteins can be stimulatory for <i>O. oeni</i>. The mannoprotein concentration in wine depends on the fermenting yeasts, and non-<i>Saccharomyces</i> in particular can increase it. As a result of the hydrolytic activity of <i>O. oeni</i>, these macromolecules can be degraded, and the released mannose can be taken up and used as an energy source by the bacterium. Here we look at mannoprotein consumption and the expression of four <i>O. oeni</i> genes related to mannose uptake (<i>manA</i>, <i>manB</i>, <i>ptsI,</i> and <i>ptsH</i>) in a wine-like medium supplemented with mannoproteins and in natural wines fermented with different yeasts. We observe a general gene upregulation in response to wine-like conditions and different consumption patterns in the studied media. <i>O. oeni</i> was able to consume mannoproteins in all the wines. This consumption was notably higher in natural wines, especially in <i>T. delbrueckii</i> and <i>S. cerevisiae</i> 3D wines, which presented the highest mannoprotein levels. Regardless of the general upregulation, it seems that mannoprotein degradation is more closely related to the fermenting medium.
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