Specific gene regulations of non-usual micronutrient starvations leading to cell death during wine fermentation

Camille Duc,Catherine Tesnière,Bruno Blondin,Isabelle Sanchez,Martine Pradal,Jessica Noble

doi:10.20870/oeno-one.2020.54.2.2970

Abstract

Yeast cell death can occur during wine alcoholic fermentation, leading to stuck fermentations, which are a major issue for winemakers. Cell death is generally considered to result from ethanol stress that negatively affects membrane integrity. However, it has been recently found that yeast cell death is also related to nitrogen metabolism. Indeed, nitrogen starvation is one of the most frequently encountered starvations in oenological conditions, and yeast is correspondingly able to cope with these deficiencies. However, cell death can also result from yeast inability to implement an appropriate stress response under some conditions of nutrient limitations, most likely not encountered by yeast in the wild. More specifically, a set of micronutrients (oleic acid, ergosterol, pantothenic acid and nicotinic acid) was identified that led to cell death when present in low, growth-restricting concentrations. After an examination of gene expression under conditions of imbalance between nitrogen and these non-traditional micronutrients, it appeared that, in addition to already identified mechanisms of gene regulation in relation to nitrogen metabolism, some genes had specific deficiency regulations that may also explain some of the observed cell mortality. Our data include specific regulations of certain key genes of lipid metabolism as well as others concerning DNA stability under unusual deficiency conditions. Our work allows us to propose a model of the mechanisms involved in controlling yeast mortality under oenological fermentation conditions.

Highlights

Grape must is a complex medium composed of many nutrients such as nitrogen, sugars, lipids or vitamins (Duc et al, 2017; Gobert et al, 2019; Tesnière, 2019)
As a result of these assays, we were able to find that an ergosterol, oleic acid, pantothenic acid or nicotinic acid starvation can lead to cell death during wine fermentation
For : N-: low nitrogen, 71 mg/L YAN; N-/Erg- : low nitrogen/low ergosterol, 71 mg/L YAN, 1.5 mg/L ergosterol; N+/Ole-: high nitrogen/low oleic acid, 425 mg/L YAN, 18 mg/L oleic acid; N+/Erg-: high nitrogen/low ergosterol, 425 mg/L YAN, 1.5 mg/L ergosterol; N+/Pan-: high nitrogen/low pantothenic acid, 425 mg/L YAN, 0.02 mg/L pantothenic acid and N+/Nic-: high nitrogen/low nicotinic acid, 425 mg/L YAN, 0.08 mg/L nicotinic acid; transcriptomic assays were performed at four time-points during alcoholic fermentation (T1, 20 106 cells/mL; T2, 12 g CO2 produced; T3, 40 g CO2 produced; T4, 75 g CO2 produced) indicated by the grey triangle

Summary

Introduction

Grape must is a complex medium composed of many nutrients such as nitrogen, sugars, lipids or vitamins (Duc et al, 2017; Gobert et al, 2019; Tesnière, 2019). A low nitrogen concentration in the must has been shown to be responsible for stuck or sluggish fermentations (Bely et al, 1990). These situations are often explained by a loss of yeast viability, usually attributed to insufficient lipid availability in the must. A deficiency in lipids - some of the principal components of the yeast membrane - has been shown to lead to cell death due to the inability of yeast to cope with ethanol stress at the end of the fermentation stationary phase (Alexandre et al, 1994; Casalta et al, 2016). It has been shown that the balance between nitrogen and the other nutrients is crucial for this survival (Duc et al, 2017; Tesnière et al, 2013). The nature of the nitrogen has been shown to influence the occurrence of cell death under these conditions (Duc et al, 2019)

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Conclusion