Fungal Spores Promote the Glycerol Production of Saccharomyces cerevisiae by Upregulating the Oxidative Balance Pathway.

Fungal contamination is prevalent in grape berries and unavoidable during the winemaking process. In botrytized wine, Botrytis cinerea contamination of grape berries beneficially promotes the wine flavor, which is desirable especially with high glycerol content. To investigate the underlying mechanism, Aspergillus carbonarius and B. cinerea spores were separately cocultured with two different Saccharomyces cerevisiae strains in both grape juice and synthetic nutrient media. The results showed that both A. carbonarius and B. cinerea promoted glycerol accumulation and the consumption of sugars in the coculture systems but could not synthesize glycerol by themselves. The metabolites produced by fungal spores triggered these reactions. Reverse transcription-polymerase chain reaction analysis showed that the presence of A. carbonarius spores regulated the expression of GPP1 and GPD2, indicating that the reaction was triggered by regulating the oxidative balance pathway. The study revealed the beneficial impact of fungal contamination on wine quality by influencing yeast metabolism.