Here’s an interesting journal article for the yeast wrangler in you to geek out on. Genome Sequence of Saccharomyces carlsbergensis, the World’s First Pure Culture Lager Yeast details the efforts of Andrea Walther, Ana Hesselbart and Jürgen Wendland from the Carlsberg Laboratory to get a handle on the origins of modern lager yeast using more modern gene sequencing tools. Here’s the wonderfully obtuse explanation from the Abstract:
Lager yeast beer production was revolutionized by the introduction of pure culture strains. The first established lager yeast strain is known as the bottom fermenting Saccharomyces carlsbergensis, which was originally termed Unterhefe No.1 by Emil Chr. Hansen and used in production in since 1883. S. carlsbergensis belongs to group I/Saaz-type lager yeast strains and is better adapted to cold growth conditions than group II/Frohberg-type lager yeasts, e.g. the Weihenstephan strain WS34/70. Here, we sequenced S. carlsbergensis using next generation sequencing technologies. Lager yeasts are descendants from hybrids formed between a Saccharomyces cerevisiae parent and a parent similar to Saccharomyces eubayanus. Accordingly, the S. carlsbergensis 19.5 Mb genome is substantially larger than the 12 Mb S. cerevisiae genome. Based on the sequence scaffolds, synteny to the S. cerevisae genome, and by using directed PCRs for gap closure we generated a chromosomal map of S. carlsbergensis consisting of 29 unique chromosomes. We present evidence for genome and chromosome evolution within S. carlsbergensis via chromosome loss and loss of heterozygosity specifically of parts derived from the S. cerevisiae parent. Based on our sequence data and via FACS analysis we determined the ploidy of S. carlsbergensis. This inferred that this strain is basically triploid with a diploid S. eubayanus and haploid S. cerevisiae genome content. In contrast the Weihenstephan strain, which we re-sequenced, is essentially tetraploid composed of two diploid S. cerevisiae and S. eubayanus genomes. Based on conserved translocations between the parental genomes in S. carlsbergensis and the Weihenstephan strain we propose a joint evolutionary ancestry for lager yeast strains.
If that made your head spin, try the full article, which was released in full online at the end of February. It will be published in the journal G3: Genes, Genomes, Genetics in a future issue. It’s fascinating reading.