Exploring yeast adaptation to the grape must
Résumé
Saccharomyces cerevisiae strains isolated from wine, rum, bread, or oak present a wide phenotypic
divergence (1, 3). Different genome sequencing programs by our group (2,3) and others (4) have offered
clues about the different mechanisms permitting the adaptation of yeast to wine environment. Copy
number variations, translocations, and horizontal transfers have been shown to participate in the
adaptation of Saccharomyces cerevisiae to the grape must (3,5). In contrast to the flood of genomic data,
we have very few experimental clues on how genetic variation participated in the evolution of wine yeast,
and experimental evolution is the method of choice to investigate such questions. To understand how
yeast adapted to the wine environment, we built 3 x 4 recombinant populations containing either wine
strains, Mediterranean oak strains (as a grape must naive population), and strains from both origins.
These three populations were grown, them for 24 fermentations in a Sauvignon grape must that
contained assimilable nitrogen and sterol at a non-limiting concentrations. In addition, the potential
effect of the grape must microbiota was evaluated through the addition of a synthetic microflore. After
the evolution, evolved strains were phenotyped for their ability to grow in the grape must and ferment
and compared to the ancestral population. As expected, all populations performed better at the end of
the experiment, and populations containing wine alleles outperformed the Mediterranean oak
populations. The effect of the presence of a synthetic microflore could only be slightly observed on the
maximum fermentation speed. The comparison of the genome of adapted populations to the ancestral
pool, revealed shifts in allelic frequencies in regions associated to specific molecular functions or cellular
compartment in the three adapted lineages. However, mitochondrial genes were impacted in all adapted
lineages. Interestingly, when considering the Mediterranean oak/ wine populations, the genes SSU1 and
ECM34 involved in sulfite resistance (5) or MDS3 and GCN1 involved in nitrogen management (6) were
found to participate in the adaptation to the grape. This highlights the complexity of the adaptation to
the grape must.