Low Phenotypic Penetrance and Technological Impact of Yeast [GAR +] Prion-Like Elements on Winemaking.

Ramon Gonzalez,Ana Mencher,Kiran Raosaheb Patil,Paula Jouhten,Mariana Fernández-Preisegger,Jordi Tronchoni,Alejandra Omarini,Alda Joao Rodrigues,Pilar Morales,José Antonio Curiel,Noelia Gallego,Cristina Juez,Laura López-Berges

doi:10.3389/fmicb.2018.03311

Abstract

[GAR+] prion-like elements partially relieve carbon catabolite repression in Saccharomyces cerevisiae. They have been hypothesized to contribute to wine yeast survival and alcohol level reduction, as well as communication with bacteria and stuck fermentation. In this work, we selected [GAR+] derivatives from several genetic backgrounds. They were characterized for phenotypic penetrance, heritability and confirmed as prion-like through curing by desiccation. In terms of fermentation kinetics, the impact of the prion on anaerobic wine fermentation (natural grape juice) was either neutral or negative, depending on the genetic background. Likewise, residual sugars were higher or similar for [GAR+] as compared to the cognate [gar-] strains. The prions had little or no impact on glycerol and ethanol yields; while acetic acid yields experienced the highest variations between [GAR+] and [gar-] strains. Strains analyzed under aerobic conditions followed the same pattern, with either little or no impact on fermentation kinetics, ethanol or glycerol yield; and a clearer influence on volatile acidity. Although no clear winemaking advantages were found for [GAR+] strains in this work, they might eventually show interest for some combinations of genetic background or winemaking conditions, e.g., for reducing acetic acid yield under aerated fermentation.

Highlights

Saccharomyces cerevisiae is the main yeast species responsible for alcoholic fermentation of many traditional foods and beverages
The paradigm of carbon catabolite repression (CCR) being clearly advantageous for microbial species was somewhat challenged by the discoveries around the [GAR+] prion-like element in S. cerevisiae. [GAR+] is a proteinbased heritable element that allows yeast circumvent CCR, so becoming a metabolic generalist, in contrast to the specialization for glucose shown by wild-type strains (Brown and Lindquist, 2009)
Six different genetic backgrounds were used for this purpose. [GAR+] strains were identified as described in Section “Materials and Methods” and by Brown and Lindquist (2009)

Summary

Introduction

Saccharomyces cerevisiae is the main yeast species responsible for alcoholic fermentation of many traditional foods and beverages. It exhibits alcoholic fermentation even under aerobic conditions, making it an archetypical Crabtree-positive yeast. Several biological mechanisms contribute to the Crabtree effect, including carbon catabolite repression (CCR) of mitochondrial and respiration related genes (Schüller, 2003; Kayikci and Nielsen, 2015). The paradigm of CCR being clearly advantageous for microbial species was somewhat challenged by the discoveries around the [GAR+] prion-like element in S. cerevisiae. [GAR+] is a proteinbased heritable element that allows yeast circumvent CCR, so becoming a metabolic generalist, in contrast to the specialization for glucose shown by wild-type strains (Brown and Lindquist, 2009). The capability of relieving glucose repression has been proposed as an evolutionarily conserved mechanism of bethedging in fluctuating environments, providing some adaptive advantage, e.g., rapid reversibility, over DNA mutation (Jarosz et al, 2014b)

Methods

Results

Conclusion