Abstract
BackgroundIn wine fermentation starter cultures, the blending of non-Saccharomyces yeast with Saccharomyces cerevisiae to improve the complexity of wine has become common practice, but data regarding the impact of co-cultivation on yeast physiology and on genetic and metabolic regulation remain limited. Here we describe a transcriptomic analysis of mixed fermentations of Saccharomyces cerevisiae and Lachancea thermotolerans. The fermentations were carried out in carefully controlled environmental conditions in a bioreactor to reduce transcriptomic responses that would be due to factors other than the presence of the second species.ResultsThe transcriptomic data revealed that both yeast species showed a clear response to the presence of the other. Affected genes primarily belonged to two groups: genes whose expression can be linked to the competition for certain trace elements such as copper and iron, as well as genes required for cell wall structure and integrity. Furthermore, the data revealed divergent transcriptional responses with regard to carbon metabolism in response to anoxic conditions.ConclusionsThe results suggest that the mixed fermentation created a more competitive and stressful environment for the two species than single strain fermentations independently from total biomass, i.e. competition between cells of the same species is less stressful, or may present a different set of challenges, than interspecies competition. The changes in cell wall and adhesion properties encoding genes suggest that the adjustment of physical contact between cells may play a direct role in the response to the presence of competing species.
Highlights
In wine fermentation starter cultures, the blending of non-Saccharomyces yeast with Saccharomyces cerevisiae to improve the complexity of wine has become common practice, but data regarding the impact of co-cultivation on yeast physiology and on genetic and metabolic regulation remain limited
We evaluated the transcriptomic response of L. thermotolerans and S. cerevisiae in mixed fermentations when compared to single strain cultures in the same environmental conditions
The specific growth rate of S. cerevisiae and L. thermotolerans monocultures under anaerobic conditions, was found to be 0.2 h− 1 at a dilution rate of 0.1 h− 1 and 0.17 h− 1 at a dilution rate of 0.075 h− 1, respectively, and similar cell concentrations were obtained (Table 1)
Summary
In wine fermentation starter cultures, the blending of non-Saccharomyces yeast with Saccharomyces cerevisiae to improve the complexity of wine has become common practice, but data regarding the impact of co-cultivation on yeast physiology and on genetic and metabolic regulation remain limited. The data strongly suggest the existence of specific physical and metabolic interactions between yeast species, but do not provide any insights about the molecular mechanism behind such interactions, and little is known about the molecular factors influencing the response of any yeast species to the presence of another species Such studies are challenging because of the complexity of multispecies systems and of ecological interactions. DNA microarray-based transcriptome analyses and mass spectrometry-based proteome analyses have been used to study the interaction between yeast and bacteria as well as between S. cerevisiae and non-Saccharomyces yeasts under oenological conditions [17,18,19,20,21,22,23,24] These studies have usually relied on batch fermentation conditions. Such conditions make it difficult to differentiate the relative impact of the continuous changes in media composition from the specific response of one yeast species to the presence of the other
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