Electrophoretic karyotyping as a taxonomic tool in the genus Saccharomyces.

The electrophoretic karyotypes of strains of the ten species of the yeast genus Saccharomyces (sensu Vaughan-Martini & Martini 1992) were determined by the CHEF (contour-clamped homogeneous electric field) system of pulsed field gel electrophoresis. The number of bands was found to vary from 6 to 17 and the calculated molecular weights of haploid genomes ranged from 7.9 to 14.6 Mbp. The type strains of S. exiguus and the four species of the Saccharomyces sensu stricto complex (S. bayanus, S. cerevisiae, S. paradoxus and S. pastorianus) have genomes comprised of chromosomes of all three size classes: light (< 500 kb), medium (500-1000 kb) and heavy (> 1,000 kb). Saccharomyces kluyveri DNA has only heavy bands, while the remaining species exhibit medium and heavy chromosomes. When more than one strain of each species was examined, it was seen that while the species S. bayanus, S. castellii, S. cerevisiae, S. kluyveri, S. paradoxus and S. pastorianus showed uniform karyotypes, S. dairensis, S. exiguus, S. servazzii and S. unisporus comprise heterogeneous taxa.