Influence of nitrogen source on expression of genes involved in aroma production in Saccharomyces uvarum

Abstract

Saccharomyces uvarum has interesting properties that can be exploited for the production of fermented beverages. Particularly, the cryotolerance and capacity to produce high amounts of volatile compounds offers new opportunities for the wine industry. Besides the contribution of the nitrogen source to primary metabolism, some nitrogen compounds are precursors of volatile molecules that produce aroma. The nitrogen compounds assimilated by yeast are classified as rich or poor nitrogen sources depending on how they affect the growth and the nitrogen regulation mechanisms. In S. cerevisiae, the nitrogen metabolism is well understood but less is known about these pathways in S. uvarum. The aim here is to understand the nitrogen metabolism in S. uvarum and the effects of the nitrogen source on the production of aroma volatiles at low temperature; the focus is on temperatures below 20°C since this is relevant for wine production. First, nitrogen preference was established using 10 different compounds as sole nitrogen sources for S. uvarum and S. cerevisiae: important differences were found in the efficiency of asparagine to support growth. The alcoholic fermentations done in synthetic must, showed the same pattern of nitrogen consumption in each species. Afterwards, comparative analysis of gene expression (RNAseq) of S. uvarum MTF3098 was carried out in ammonium, methionine, phenylalanine and asparagine to determine how the nitrogen source affects the expression of key genes involved in nitrogen metabolism and aroma production. The transcriptome data revealed substantial changes in expression patterns of nitrogen metabolism genes. The gene clusters with highest fold change when comparing inorganic nitrogen source (ammonium) and organic source (methionine, phenylalanine, asparagine) in S. uvarum MTF3098 were genes encoding transporters and proteins responsible for aroma synthesis; using amino acids as sole nitrogen source instead of ammonium resulted in an increased expression of this group of genes. This study increases understanding of the importance of the nitrogen source in the aroma production of Saccharomyces yeasts and broads the knowledge on S. uvarum aroma production for applications in wine industry. Ongoing work includes correlating transcriptome and volatile metabolome data to understand links between gene expression and aroma production in S. uvarum.