## 4 Discussion  
Bioprospecting can guide producers in the choice of indigenous yeast strains that can bring new and interesting flavors while reducing the risks of failure that are more common in spontaneous winemaking. In our research, among the eight domains of southwestern Switzerland, we collected a total of seven major genera of indigenous yeasts, with _Metschnikowia_ being the most abundant in the sample analyzed. A large number of studies have shown that the diversity of the microbiome (including fungi, yeasts, and bacteria) present in vineyards certainly depends on the location but also on the grape variety and cultivation method [11; 26]. The most frequently isolated yeasts were the genera _Hansenispora_ and _Metschnikowia_, according to [PERSON] et al. [27], [PERSON] et al. [28], and [PERSON] et al. [29], which is congruent with our results. However, a theoretical explanation for the high frequency of _Metschnikowia_ spp. found is that the presence of the yeast could be favored by the pressure of _Botrytis cinerea_[30]. In the Swiss vineyards of vintage 2021, after the second half of September, several rains favored the _Botrytis_ infection, but due to the low temperatures, the grapes remained healthy [31]. We decided to focus our attention on _Metschnikowia_ because it is one of the most interesting genera today from an oenological perspective. To the best of our knowledge, this is the first time that _Metschnikowia_ species have been systematically isolated and characterized in southwestern Switzerland. These 30 isolates of the genus _Metschnikowia_ were used for a first experimental winemaking at bench scale, and we showed high variability among the oenological parameters of interest, already reported for _M. pulcherrima_ species [32], and no significant differences were found among the four main species (_M. pulcherrima_, _M. fructicola_, _M. reukaufii_, _M. gruessii_). The candidate yeast for further experiments had to meet two main criteria: high production of higher alcohols, such as 2-phenylethanol, which gives a \"rose\" bouquet [33], and low production of compounds that can lead to undesirable aromas when present in high concentrations, such as acetaldehyde [34]. We therefore selected a yeast belonging to the Vaud region that had these characteristics. It should be noted that location was another important factor in the final selection, since proximity of the domain to our analytical laboratories facilitated the study of the ecology of this indigenous strain in subsequent vintages. Next, we tested the selected strain of _M. pulcherrima_ in another microvinification experiment to understand its compatibility with _S. cerevisiae_ in co-fermentations and to highlight potential adverse effects. Our results showed that _M. pulcherrima_ did not ferment sugars during the first 5 days and that it did not prevent or limit the fermentative power of the _Saccharomyces_ after inoculation. However, this result prompted us to test the viability of _M. pulcherrima_ in fermentation. We then used FCM to study its physiological state and to rule out the possibility that the Chasselas must used had a negative effect on the viability of the yeast. Our results showed high levels of CFDA fluorescence exhibited by _M. pulcherrima_, and no dead PI-positive cells were detected until at least day 5. In addition, _M. pulcherrima_ showed active proliferation until _S. cerevisiae_ was added. It is interesting that this double staining, together with the nucleic acid dye Syto-41 and the analysis of the control samples (_M. pulcherrima_ fermentations prior to _S. cerevisiae_ co-inoculation), allowed us to discriminate the two different types of yeast in co-fermentation. Specifically, we examined the fluorescence intensity of CFDA and Syto 41 in the cell populations at the different sampling points. It should be noted, however, that the absolute specificity of this discrimination method cannot be guaranteed, since these dyes are commonly used in microbiology and are not specific for a given yeast type.