Saccharomyces cerevisiae accumulates GAPDH-derived peptides on its cell surface that induce death of non-Saccharomyces yeasts by cell-to-cell contact.

During wine fermentations, Saccharomyces cerevisiae starts to excrete antimicrobial peptides (AMPs) into the growth medium that induce death of non-Saccharomyces yeasts at the end of exponential growth phase (24-48 h). Those AMPs were found to derive from the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). On the other hand, the early death of non-Saccharomyces yeasts during wine fermentations was also found to be mediated by a cell-to-cell contact mechanism. Since GAPDH is a cell-wall-associated protein in S. cerevisiae, we put forward the hypothesis that the GAPDH-derived AMPs could accumulate on the cell surface of S. cerevisiae, thus inducing death of non-Saccharomyces yeasts by cell-to-cell contact. Here we show that 48-h grown (stationary phase) cells of S. cerevisiae induce death of Hanseniaspora guilliermondii and Lachancea thermotolerans by direct cell-to-cell contact, while 12-h grown cells (mid-exponential phase) do not. Immunological tests performed with a specific polyclonal antibody against the GAPDH-derived AMPs revealed their presence in the cell wall of S. cerevisiae cells grown for 48 h, but not for 12 h. Taken together, our data show that accumulation of GAPDH-derived AMPs on the cell surface of S. cerevisiae is one of the factors underlying death of non-Saccharomyces yeasts by cell-to-cell contact.

Influence of nitrogen sources on growth and fermentation performance of different wine yeast species during alcoholic fermentation.

In this study, the influence of twenty different single (i.e. 19 amino acids and ammonium sulphate) and two multiple nitrogen sources (N-sources) on growth and fermentation (i.e. glucose consumption and ethanol production) performance of Saccharomyces cerevisiae and of four wine-related non-Saccharomyces yeast species (Lachancea thermotolerans, Metschnikowia pulcherrima, Hanseniaspora uvarum and Torulaspora delbrueckii) was investigated during alcoholic fermentation. Briefly, the N-sources with beneficial effects on all performance parameters (or for the majority of them) for each yeast species were alanine, arginine, asparagine, aspartic acid, glutamine, isoleucine, ammonium sulphate, serine, valine and mixtures of 19 amino acids and of 19 amino acids plus ammonium sulphate (for S. cerevisiae), serine (for L. thermotolerans), alanine (for H. uvarum), alanine and asparagine (for M. pulcherrima), arginine, asparagine, glutamine, isoleucine and mixture of 19 amino acids (for T. delbrueckii). Furthermore, our results showed a clear positive effect of complex mixtures of N-sources on S. cerevisiae and on T. delbrueckii (although to a lesser extent) as to all performance parameters studied, whereas for L. thermotolerans, H. uvarum and M. pulcherrima, single amino acids affected growth and fermentation performance to the same extent as the mixtures. Moreover, we found groups of N-sources with similar effects on the growth and/or fermentation performance of two or more yeast species. Finally, the influences of N-sources observed for T. delbrueckii and H. uvarum resembled those of S. cerevisiae the most and the least, respectively. Overall, this work contributes to an improved understanding of how different N-sources affect growth, glucose consumption and ethanol production of wine-related yeast species under oxygen-limited conditions, which, in turn, may be used to, e.g. optimize growth and fermentation performance of the given yeast upon N-source supplementation during wine fermentations.