Genetic analysis of the non-sporulating phenotype of brewer's yeasts

The ploidies and sporulation abilities of six brewer's yeasts were examined. One (YB11-1) out of the six was triploid and sporulating, another (IFO2031) was haploid, and the others (IFO1167, IFO2003, S341 and YB3-7) were diploid and non-sporulating. The five non-sporulating strains did not have the premeiotic DNA synthesis. Their non-sporulating phenotypes were genetically analyzed by examining the sporulation abilities of hybrids between brewer's yeasts and standard genetic strains of Saccharomyces cerevisiae. All non-sporulating brewer's yeasts complemented 32 sporulation-deficient mutations (spoT–spoT23, spo1–spo5, spo7, spo8, spo10, and spo11). Hybrids between brewer's yeasts and haploid or diploid strains homozygous for the mating-type locus had poor or no sporualtion. On the contrary, hybrids between brewer's yeasts and diploid strains heterozygous for the mating-type locus sporulated at a high frequency. These results indicated that the non-sporulating phenotype of brewer's yeasts was caused by a deficiency of the mating-type genes rather than by mutations of sporulation genes. The Southern hybridization probed with the MATa gene showed polymorphisms in mating-type genes of brewer's yeasts.