Sterol uptake analysis in Saccharomyces and non-Saccharomyces wine yeast species

Sterols are essential components of the yeast membrane and their synthesis requires oxygen. Yet, Saccharomyces cerevisiae has developed the ability to take up sterols from the medium under anaerobiosis. Here we investigated sterol uptake efficiency and the expression of genes related to sterol import in Saccharomyces and non-Saccharomyces wine yeast species fermenting under anaerobic conditions. The sterol uptake efficiency of 39 strains was evaluated by flow cytometry (with 25-NBD Cholesterol, a fluorescent cholesterol probe introduced in the medium) and we found an important discrepancy between Saccharomyces and non-Saccharomyces wine yeast species that we correlated to a lower final cell population and a lower fermentation rate. A high uptake of sterol was observed in the various Saccharomyces strains. Spot tests performed on 13 of these strains confirmed the differences between Saccharomyces and non-Saccharomyces strains, suggesting that the presence of the sterol uptake transporters AUS1 and PDR11 could cause these discrepancies. Indeed, we could not find any homologue to these genes in the genome of Hanseniaspora uvarum, H. guillermondii, Lachancea thermotolerans, Torulaspora delbreueckii, Metschnikowia pulcherrima, or Starmarella bacillaris species. The specialization of sterol import function for post genome-duplication species may have favored growth under anaerobiosis.