The hexose transporters of Saccharomyces cerevisiae play different roles during enological fermentation

We investigated the role of hexose transporters in a Saccharomyces cerevisiae strain derived from an industrial wine strain by carrying out a functional analysis of HXT genes 1-7 under enological conditions. A strain in which the sugar carrier genes HXT1-HXT7 were deleted was constructed and the HXT genes were expressed individually or in combination to evaluate their role under wine alcoholic fermentation conditions. No growth or fermentation was observed in winemaking conditions for the hxt1-7 delta strain. The low-affinity carriers Hxt1 and Hxt3 were the only carriers giving complete fermentation of sugars when expressed alone, indicating that these carriers play a predominant role in wine fermentation. However, these two carriers have different functions. The Hxt3 transporter is thought to play a major role, as it was the only carrier that gave an almost normal fermentation profile when produced alone. The hxt1 carrier was much less effective during the stationary phase and its role is thought to be restricted to the beginning of fermentation. The high-affinity carriers Hxt2, Hxt6 and/or Hxt7 were also required for normal fermentation. These high-affinity transporters have different functions: hxt2 is involved in growth initiation, whereas Hxt6 and/or Hxt7 are required at the end of alcoholic fermentation. This work shows that the successful alcoholic fermentation of wine involves at least four or five hexose carriers, playing different roles at various stages in the fermentation cycle.