Nitrogen metabolism in Kluyveromyces marxianus and Saccharomyces cerevisiae: towards a better understanding of fermentation aroma production

Abstract

During wine alcoholic fermentation, yeasts produce volatile aroma compounds from sugar and nitrogen metabolism. Some of the metabolic pathways leading to these compounds have been known for more than a century. Yet, the differences in compound yield and nature between species remain poorly understood. Using a two-pronged approach of isotopic filiation and transcriptome analysis, this study endeavoured to shed new light on the utilisation of nitrogen sources by two wine-related yeast species, Saccharomyces cerevisiae Lalvin EC1118® (Lallemand) and Kluyveromyces marxianus IWBT Y885. 

The data showed that, although the order and intensity of uptake of nitrogen sources was broadly similar, those of ammonium and arginine differed. Furthermore, the utilisation of assimilated amino acids also differed significantly. While S. cerevisiae redistributed the nitrogen in these amino acids evenly for the production of other amino acids, K. marxianus clearly favoured specific amino acids. As for amino acids used as substrates for the production of aroma compounds, the fate of leucine and valine did not differ significantly between the two species. However, phenylalanine metabolism differed, and a larger proportion of phenylalanine was channelled through the Ehrlich pathway in K. marxianus, resulting in increased production of phenylethanol. Transcriptome data suggest that this shift can be explained by the higher expression of aromatic amino transferases in K. marxianus. Taken together, the data show that metabolic pathways are broadly conserved, but that individual nitrogen sources are not always assimilated and metabolised in identical ways. The study also provides new insights on the modulation of fermentative aroma profiles by yeast species of commercial interest.