Abstract
Different populations within a species represent a rich reservoir of allelic variants, corresponding to an evolutionary signature of withstood environmental constraints. Saccharomyces cerevisiae strains are widely utilised in the fermentation of different kinds of alcoholic beverages, such as, wine and sake, each of them derived from must with distinct nutrient composition. Importantly, adequate nitrogen levels in the medium are essential for the fermentation process, however, a comprehensive understanding of the genetic variants determining variation in nitrogen consumption is lacking. Here, we assessed the genetic factors underlying variation in nitrogen consumption in a segregating population derived from a cross between two main fermenter yeasts, a Wine/European and a Sake isolate. By linkage analysis we identified 18 main effect QTLs for ammonium and amino acids sources. Interestingly, majority of QTLs were involved in more than a single trait, grouped based on amino acid structure and indicating high levels of pleiotropy across nitrogen sources, in agreement with the observed patterns of phenotypic co-variation. Accordingly, we performed reciprocal hemizygosity analysis validating an effect for three genes, GLT1, ASI1 and AGP1. Furthermore, we detected a widespread pleiotropic effect on these genes, with AGP1 affecting seven amino acids and nine in the case of GLT1 and ASI1. Based on sequence and comparative analysis, candidate causative mutations within these genes were also predicted. Altogether, the identification of these variants demonstrate how Sake and Wine/European genetic backgrounds differentially consume nitrogen sources, in part explaining independently evolved preferences for nitrogen assimilation and representing a niche of genetic diversity for the implementation of practical approaches towards more efficient strains for nitrogen metabolism.
Highlights
Yeast strains isolated from various geographic origins have long been recognised as the main microorganisms underlying a number of fermentation processes [1]
Saccharomyces cerevisiae isolates have been widely utilised in the industry for the alcoholic fermentation of different kinds of beverages, representing a rich reservoir of genetic variants selected upon their fermentation capacity within these environments [2]
We divided the total amount of nitrogen into 15 different traits corresponding to ammonium and 14 amino acids, because these are known to be used as nitrogen sources at this stage [33]
Summary
Yeast strains isolated from various geographic origins have long been recognised as the main microorganisms underlying a number of fermentation processes [1]. S. cerevisiae is the principal species responsible for the alcoholic fermentation, producing and tolerating high ethanol levels [4,5,6] During this process, S. cerevisiae is exposed to severe osmotic stresses with high sugar concentrations and low availability of nitrogen respect to carbon. Adequate nitrogen levels in the medium are essential for a good fermentation, since low levels can prompt slow fermentations or even stop the process, causing important economic losses [13] To avoid this problem, grape must is sometimes supplemented with ammonium salts, excesses of inorganic nitrogen can induce the production of toxic ethyl carbamate and alter yeasts’ amino acid preferences and wine aromatic properties [14]. These facts highlight the need for superior strains with efficient yields on nitrogen consumption to reduce practices that could alter the final fermentation product
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