Copper-based grape pest management has impacted wine aroma

Abstract

Despite the high energetic cost of the reduction of sulfate to H₂S, required for the synthesis of sulfur-containing amino acids, some wine Saccharomyces cerevisiae strains have been reported to produce excessive amounts of H₂S during alcoholic fermentation, which is detrimental to wine quality. Surprisingly, in the presence of sulfite, used as a preservative, wine strains produce more H₂S than wild (oak) or wine velum (flor) isolates during fermentation. Since copper resistance caused by the amplification of the sulfur rich protein Cup1p is a specific adaptation trait of wine strains, we analyzed the link between copper resistance mechanism, sulfur metabolism and H₂S production. We show that a higher content of copper in the must increases the production of H₂S, and that SO₂ increases the resistance to copper. Using a set of 51 strains we observed a positive and then negative relation between the number of copies of CUP1 and H₂S production during fermentation. This complex pattern could be mimicked using a multicopy plasmid carrying CUP1, confirming the relation between copper resistance and H₂S production. The massive use of copper for vine sanitary management has led to the selection of resistant strains at the cost of a metabolic tradeoff: the overproduction of H₂S, resulting in a decrease in wine quality.

Figure 1

Difference in the average of cumulate H₂S production during alcoholic fermentation of velum, oak and wine strains in absence (A) or presence (B) of SO₂.

Figure 2

Effect of copper content in synthetic must without SO₂ on total H₂S production during alcoholic fermentation by wine strains VL1 and LMD17. p values refer to two-way ANOVA.

Figure 3

H₂S production (in synthetic must without SO₂) distribution as function of CUP1 copy number of each strain. (A) Whole set of studied strains, in synthetic must without SO₂; (B) whole set of studied strains, in synthetic must supplemented with SO₂; (C) wine strains, in synthetic must without SO₂; (D) wine stains in synthetic must supplemented with SO₂; Isolation origins are described by colours as in Fig. 1. Black solid line: polynomial model describing the relation between H₂S production and CUP1 copy number; red line: same model excluding the two highest H₂S producers.

Figure 4

Effect of CUP1 overexpression on total H₂S released during alcoholic fermentation (in synthetic must without SO₂) in three S. cerevisiae strains. Different lowercase letters indicate statistically significant differences between the molecular modifications (control wild-type strain, empty vector or CUP1 overexpressing vector) for each strain separately, after Tukey multiple comparison of means at 95% family-wise confidence level.

Figure 5

Effect of SO₂ addition in the media on copper resistance. (A) Resistance of oak strain Oak-Rom 3.2 to copper (0 to 1 mM) in the absence (control) and presence of 40 mg/L SO₂. (B) Resistance of wine strain LMD17 and L1374 to copper (0 to 12 mM) in the absence (control) and presence of SO₂ (60 mg/L).

Figure 6

Experimental design.