Effect of low temperature fermentation on yeast nitrogen metabolism.
Gemma Beltran (1), Maite Novo (1), Nicolas Rozès (1), Albert Mas (1), Ricardo Cordero (2), José M. Guillamón (1)
(1) Bioquímica i Biotecnologia, Universitat Rovira i Virgili, Marceli Domingo s/n, Tarragona, 43007, Spain; (2) Dep. of Viticulture & Oenology, Institute for Wine Biotechnology, Stellenbosch University. Victoria St. Matieland-7602, Stellenbosch, South Africa.
Temperature of fermentation is an important factor in winemaking due to its influence in fermentation performance and in final product characteristics. Fermentation temperature is also an important factor determining the utilization of nitrogen sources during fermentation. Low temperature decreased biomass yield and relaxed the nitrogen catabolite repression. As a consequence, ammonium and glutamine, which are the preferred source for biomass production, were less consumed at low temperature. Likewise amino acids, which are only taken up under derepressed conditions (Arg, Glu, Ala), were more consumed at low temperature. Another amino acid whose uptake increased at low temperature is tryptophan. The uptake of tryptophan as a rate-limiting step in growth at low temperature has already been reported. The expression of the nitrogen transporters GAP1 and MEP2 was analysed, and the nitrogen catabolite repression of these permeases seemed to be less efficient at 13°C, where we obtained higher values of gene expression. Our results pointed to a different nitrogen regulation at low temperature, which can affect to the growth rate and nitrogen preferences. In a global transcriptomic analysis of S. cerevisiae, some genes associated with nitrogen transport and metabolism were importantly up-regulated in yeast cells fermenting grape must at low temperature. This transcriptomic data has been corroborated by the study of different mutant strains of some nitrogen-related genes.