Use of electrophoretic karyotyping and DNA-DNA hybridization in yeast identification.

Contour-clamped homogeneous electric field (CHEF) gel electrophoresis was used to separate intact, chromosome-size DNA of different species of Saccharomyces and Zygosaccharomyces. Strains of the same Saccharomyces species had similar electrophoretic karyotypes. However, reproducible differences between individual bands indicated that strain-specific chromosome length polymorphism (CLP) is widely spread in these organisms. Strains of Zygosaccharomyces spp. showed karyotype differences beyond chromosome length polymorphism. A new, DNA-DNA hybridization technique was developed to test conspecificity, using individual chromosomes as templates to prepare randomly primed, radioactive probes. Under our conditions of stringency, species and chromosome-specific hybridization reactions were achieved with these probes. Using isolated chromosomes of Sacch. cerevisiae, Sacch. bayanus, and Zygosacch. rouxii as templates for probe preparation, conspecificity of strains was established, and closely related yeast species were distinguished with high reproducibility. This method is an efficient tool for studying genetic diversity of a given yeast species. Also, it can assist in yeast species identification and taxonomy.