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Analysis of the genetic variability in the species of the Saccharomyces sensu stricto complex

Random amplified polymorphic DNA–polymerase chain reaction (RAPD–PCR) analysis was applied to differentiate the sibling species Saccharomyces bayanus, S. cerevisiae, S. paradoxus and S. pastorianus, which constitute the most common strains of the Saccharomyces sensu stricto complex. Six decamer primers of arbitrary sequences were used to amplify the DNA of 58 strains. Species‐specific (diagnostic) bands were obtained for each species. Two phylogenetic trees constructed by the neighbour‐joining and maximum parsimony methods clearly showed that the delimitation of these related yeast species is possible by using RAPD analysis. Four groups of strains, corresponding to the species S. bayanus, S. cerevisiae, S. paradoxus and S. pastorianus, were obtained. Within the S. bayanus taxon, two groups of strains were observed. One includes the former type strain of S. uvarum, CECT1969T, and closely related wine strains (S. bayanus var. uvarum), whilst the other contains S. bayanus type strain CECT1941T and strains CECT1991 and 10513 (S. bayanus var. bayanus). The heterogeneous S. paradoxus group was divided into three lineages, corresponding to different geographic origin, American, Japanese and European populations. In addition, due to the multilocus nature of the RAPD–PCR marker, this method is both useful and appropriate for the identification of the hybrid origin of S. pastorianus. The hybrid nature was deduced from the analysis of the fraction of bands shared by each hybrid strain and the parental species. Among the 58 strains analysed, six S. pastorianus strains were hybrids, although the fraction of genome coming from each parent varied depending on the strain. Copyright © 2003 John Wiley & Sons, Ltd.