Restriction fragment length polymorphism of mitochondrial DNA (mtDNA-RFLP)
The S. cerevisiae strains described in Table 1 were subjected to mtDNA restriction analysis (24). First, 20 μg of the total DNA was digested overnight at 37°C with 40 units of HinfI restriction endonuclease (Thermo Scientific, USA) in a final volume of 50 μl. Digested DNA fragments were separated on 1.2% agarose gel in 1X TBE buffer (Tris, Borate and EDTA), stained with ethidium bromide and visualized under a UV light. The correlation of similarities among banding profiles was analyzed using Unweighted Paired Group Average (UPGMA) cluster analysis based on the Dice coefficient, using PyElph software version 1.4.
Species-specific PCR amplification
Species-specific PCR amplifications were performed as described by Pereira et al. (25). Briefly, two different sets of PCR primers were used to amplify the HO region from the genomic DNA samples of the laboratory strains and natural isolates listed in Table 1. One set of PCR primers, (ScHO-F and ScHO-R) generated a single amplicon of 400 bp when S. cerevisiae genomic DNA was used as template. The same primer set generated a 300 bp PCR amplicon with Saccharomyces pastorianus genomic DNA. However, a second set of PCR primers (LgHO-F/LgHO-R) generated a 700 bp PCR amplicon with Saccharomyces bayanus genomic DNA. These primers did not generate any PCR amplicons with non-Saccharomyces yeast genomic DNA.