Comparative transcriptional analysis of flavour-biosynthetic genes of a native Saccharomyces cerevisiae strain fermenting in its natural must environment, vs. a commercial strain and correlation of the genes\u2019 activities with the produced flavour compounds

Maria Parapouli,Angelos Perisynakis,Nikolaos Monokrousos,Efstathios Hatziloukas,Afroditi Sfakianaki

doi:10.1186/s40709-019-0096-8

Maria Parapouli, Angelos Perisynakis + Show 3 more

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https://doi.org/10.1186/s40709-019-0096-8

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Abstract

BackgroundDuring alcoholic fermentation, Saccharomyces cerevisiae synthesizes more than 400 different compounds with higher alcohols, acetate esters of higher alcohols and ethyl esters of medium-chain fatty acids being the most important products of its metabolism, determining the particular flavour profile of each wine. The concentration of the metabolites produced depends to a large extent on the strain used. The use of indigenous strains as starting cultures can lead to the production of wines with excellent organoleptic characteristics and distinct local character, superior in quality when compared to their commercial counterparts. However, the relationship of these wild-type genotypes, linked to specific terroirs, with the biosynthetic profiles of flavour metabolites is not completely clarified and understood. To this end, qRT-PCR was employed to examine, for the first time on the transcriptional level, the performance of an indigenous Saccharomyces cerevisiae strain (Z622) in its natural environment (Debina grape must). The expression of genes implicated in higher alcohols and esters formation was correlated with the concentrations of these compounds in the produced wine. Furthermore, by applying the same fermentation conditions, we examined the same parameters in a commercial strain (VL1) and compared its performance with the one of strain Z622.ResultsStrain Z622, exhibited lower concentrations of 2-methylbutanol, 3-methylbutanol and 2-phenyl ethanol, than VL1 correlating with the elevated expression levels of transaminase and decarboxylase genes. Furthermore, the significantly high induction of ADH3 throughout fermentation of Z622 probably explains the larger population numbers reached by Z622 and reflects the better adaptation of the strain to its natural environment. Regarding acetate ester biosynthesis, Z622 produced higher concentrations of total acetate esters, compared with VL1, a fact that is in full agreement with the elevated expression levels of both ATF1 and ATF2 in strain Z622.ConclusionsThis study provides evidence on the transcriptional level that indigenous yeast Z622 is better adapted to its natural environment able to produce wines with desirable characteristics, i.e. lower concentrations of higher alcohol and higher ester, verifying its potential as a valuable starter for the local wine-industry.

Highlights

During alcoholic fermentation, Saccharomyces cerevisiae synthesizes more than 400 different compounds with higher alcohols, acetate esters of higher alcohols and ethyl esters of medium-chain fatty acids being the most important products of its metabolism, determining the particular flavour profile of each wine
We have investigated the correlation of transcriptional activity of 18 genes involved in higher alcohol and ester biosynthesis, with the concentrations of the aromatic products, of an indigenous to Debina must S. cerevisiae strain (Z622) [29], which is regularly used by a wine producing company
Cell growth was monitored by two different methods, qRTPCR and plating, both proved to be of equal accuracy for cell counts, with results correlating very good with each other (R2 = 0.98591 for VL1 and R 2 = 0.99985 for Z622)

Summary

Introduction

Saccharomyces cerevisiae synthesizes more than 400 different compounds with higher alcohols, acetate esters of higher alcohols and ethyl esters of medium-chain fatty acids being the most important products of its metabolism, determining the particular flavour profile of each wine. The relationship of these wild-type genotypes, linked to specific terroirs, with the biosynthetic profiles of flavour metabolites is not completely clarified and understood To this end, qRT-PCR was employed to examine, for the first time on the transcriptional level, the performance of an indigenous Saccharomyces cerevisiae strain (Z622) in its natural environment (Debina grape must). Higher alcohols are synthesized by S. cerevisiae cells via the Ehrlich pathway, which was first reported in 1907 [9] and later modified by Neubauer and Fromherz in 1911 [10] This biosynthetic pathway consists of three steps: first, amino acids are deaminated to the corresponding α-ketoacids, in reactions catalyzed by transaminases, encoded by the genes ARO8, ARO9, BAT1 and BAT2 [6, 11, 12], with the latter being reported as the dominant gene for higher alcohols production [8]. Alcohol dehydrogenases, such as Adh1p to Adh6p and Sfa1p catalyze the reduction of aldehydes to their corresponding higher alcohols [6, 11]

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