- Genome of Lager Yeast
Thursday, October 23, 2008 7:38 PM
Subject: Genome of Lager Yeast
my brother-in-law, who is a genetics researcher...
Into the Genomics of Lager Beer Yeast [September 11, 2008]
By a GenomeWeb staff reporter
NEW YORK (GenomeWeb News) -
New genomic research suggests that the yeast strains behind crisp, clear lager-type
beers arose at least twice - probably from hybridizations involving ale yeasts.
Stanford University geneticists Barbara Dunn and Gavin Sherlock used customized
DNA microarrays and sequencing to characterize 17 different Saccharomyces pastorianus
strains from European and North American breweries. Their genomic analyses, scheduled
to appear online today in the journal Genome Research, suggest that two groups
of lager yeast resulted from independent hybridizations between baker's yeast,
Saccharomyces cerevisiae, and a cold-tolerant yeast called Saccharomyces bayanus.
Over time, these location- and brewery-specific lager yeast lineages have
undergone distinct genetic changes that provide insights into the history - and
perhaps the future - of beer production, revealing how brewing shifted from cold-sensitive
ale production to cold-tolerant lager production.
"It is likely that
each of these groups derived the S. cerevisiae portions of their genomes from
distinct but related ale yeast, and that these natural hybrids were then selected
by brewers due to their abilities to ferment at cold temperatures," Sherlock
said in a statement. "The fact that lager yeasts isolated from different
breweries each seem to have a unique genomic make-up may indicate that the yeasts
are adapting to the conditions specific to each brewery."
the most widely sold beers in the world, originated in central Europe in the Middle
Ages. They're significantly younger than ales - fruitier, full-bodied beers fermented
from S. cerevisiae - which some believe have been around for thousands of years.
One of the key differences: lagers are fermented at low temperatures, owing to
a yeast species called S. pastorianus that can ferment efficiently at low temperatures.
Although budding yeast are capable of both asexual and sexual reproduction,
S. pastorianus appears to have arisen via hybridization or fusion between yeast
cells of different species. Research in the 1980s demonstrated that S. pastorianus
is a hybrid species between S. cerevisiae and different varieties of the more
cold-tolerant yeast, including S. bayanus.
"It's possible that the
ale strain provides a certain flavor profile, while the second strain conferred
the ability to ferment at cooler temperatures," Dunn said. "Mixing them
together is a nice way for the yeast to double its genetic options."
For the latest research, Dunn and Sherlock focused on lager yeast strains
resulting from hybridizations between S. cerevisiae and S. bayanus, looking at
the genomic structure of 17 lager strains originally collected at European and
North American breweries in between 1883 and 1976.
Using array-CGH and
DNA sequencing of selected genes from lager and ale yeast strains, they classified
the S. pastorianus strains, which fell into two distinct groups correlating with
geographical location and brewery groups. From there, the duo started unraveling
the genomic architecture and ancestry patterns of each yeast group.
first group - found in Saaz beers originating in what is now the Czech Republic
and in Carlsberg brewery strains from Denmark - contained almost all of the S.
bayanus genome but had lost large sections of S. cerevisiae genome. In contrast,
the second group - collected at breweries in the Netherlands, Denmark, and North
America - contained both genomes.
Despite their differences, the researchers
were able to identify breakpoints and ploidy changes that were shared in both
lager yeast groups and clustered in certain parts of the genome.
their new understanding of the strains' genomic architecture, Dunn and Sherlock
also began reconstructing the ancestral S. pastorianus genomes. By comparing sequences
from the lager strains, three existing ale yeast strains, and 37 other S. cerevisiae
strains, the researchers determined that the two S. pastorianus groups probably
arose separately from ale yeast strains - conceivably at breweries where ale beers
were being produced.
"These long-ago brewers were practicing genetics
without even knowing it," Sherlock said in a statement. "They've given
us a very interesting opportunity to look at a relatively young, rapidly changing
species, as well as some very good beer."