Complex Nature of the Genome in a Wine-spoilage Yeast, Dekkera bruxellensis.

When the genome organization of thirty native isolates belonging to a wine-spoilage yeast Dekkera/Brettanomyces bruxellensis, a distant relative of Saccharomyces cerevisiae, was examined, the number of chromosomes varied drastically, from 4 to at least 9. When single gene probes were used in Southern analysis, the corresponding genes usually mapped to at least two chromosomal bands, excluding a simple haploid organization of the genome. When different loci were sequenced, in most cases several different haplotypes were obtained in each single isolate, and they belonged to two sub-types. Phylogenetic reconstruction using haplotypes revealed that the sequences from different isolates, belonging to one sub-type, were more similar to each other than to the sequences belonging to the other sub-type, within the isolate. Reanalysis of the genome sequence confirmed that also the partially sequenced strain Y879 is not a simple hybrid and its genome contains of app. 1% polymorphic sites. The present situation could be explained by (i) a hybridization event where two similar but different genomes have recently fused together or, (ii) that the diploid progenitor of all analyzed strains lost a regular sexual cycle and the genome started to accumulate mutations.