ABSTRACT
S. cerevisiae is used in the food industry worldwide as a principal agent of fermentation in naturally leavened bakery products, alcoholic beverages like wines, beers, fermented juices, and distillates. Strains of S. cerevisiae, thanks to their high level of resistance to ethanol, anaerobic conditions, low pH, and osmotic stress, are essentially the only organisms remaining alive at the end of wine fermentation. This yeast can be found in nature on various plants and in the soil. In studies aimed at de–ning the source from which it contaminates grapes in the vineyards and the winery environment, it has been isolated from the bodies of insects, most frequently honey bees, but also wasps and Drosophila. These are supposed to be the carriers that transfer the yeast to the interior of damaged fruits. In a phylogenetic study based on diversity at 5 loci in a sequence of 7 kb, 184 polymorphic sites were identi–ed; nucleotide variation in 81 isolates originating from natural and arti–cial fermentations, tree exudates, and immunocompromised patients from Europe, Africa, Southeast Asia, and North America supported the hypothesis that “domesticated” strains are derived from natural populations. The phylogenetic tree suggested that lineages at the root were derived from tree exudates in North America and Africa. The comparison of oak-associated and vineyard-associated yeasts suggested
70.1 Introduction ......................................................................................................................................................................615 70.1.1 Classi–cation, Morphology, and Biology .............................................................................................................615
