Diversity of the Fungal Oligopeptide Transporters in yeast and impact of oligopeptide uptake during wine fermentation
Abstract
During winemaking fermentation, the main sources of assimilable nitrogen for yeasts in grape musts are
ammonium and free amino acids; however, secondary sources such as oligopeptides are also important
contributors to the nitrogen supply. Saccharomyces cerevisiae contains different peptide transporters:
Ptr2 and Dal5, specific to di- and tri-peptides, whereas the Oligopeptide transport (OPT) family members
import tetra- and pentapeptides (1). Furthermore, Fungal Oligopeptide Transporters (FOT) are a novel
family of oligopeptide transporters found in fungi. In S. cerevisiae, at least 3 genes (FOT1, FOT2 and FOT3)
are found mainly in wine strains as a result of a horizontal gene transfer from the yeast Torulaspora
microellipsoides, which contains FOTX and FOT2Tm in tandem as well as the FOTY gene outside the
donated region to S. cerevisiae (2). In the S. cerevisiae commercial wine strain EC1118, Fot1 and Fot2 are
responsible for a broader range of oligopeptide utilization, which leads to a better fermentation efficiency
and cell viability and the production of positive organoleptic compounds in wine when compared to the
Fot-knockout strain counterparts (2, 3). These results evidenced the adaptive advantage conferred by Fot
on S. cerevisiae within the wine environment. Despite the importance of oligopeptides on yeast
metabolism during fermentation, their role has long been underestimated. In our recent work, we have
characterized oligopeptide transport in S. cerevisiae. Since Fot family members display a high sequence
identity, from 90% to 98% at gene level (2), we have explored the oligopeptide transport specificity of
each Fot member using Biolog phenotype microarrays (4). For this purpose, we have constructed S.
cerevisiae strains containing each different Fot as the sole oligopeptide transporter using CRISPR/Cas9
system. Strains expressing single FOT genes had different profiles of peptide consumption, indicating the
diversity in Fot substrate specificities. Considering the high sequence identity, this result indicated that
sequence divergence among Fot can be crucial for transport activity. In a second step of this project, we
have evaluated the effect of peptide addition on fermentation kinetics and aroma production in
oenological conditions with a large pool of commercial yeasts (5). We have compared the effect of a
“classic” assimilable nitrogen addition (ammonium + amino acids) to the addition of digested serum
albumin bovine (BSA); these fermentations were performed in both white and red musts, screening 18 S.
cerevisiae commercial strains. We showed that peptide addition enhances fermentation kinetics and
leads to specific changes in the aroma production. This work highlights the importance of peptides in
alcoholic fermentation and the oligopeptide transport diversity, providing a novel frame for nitrogen
management in oenological fermentation.