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Lager’s mystery ingredient found
By Tina Hesman Saey
Lager beers got their start in Bavaria, but
it was a little South American spice that
really kicked things off.
Scientists have known for decades that
a hybrid species of yeast, Saccharomyces
pastorianus, is the microbe that ferments
lagers. It’s also well known that one
parent of S. pastorianus is the common
baking and brewing yeast S. cerevisiae.
But the other parent of lager yeast has
eluded scientists, who have scoured
Europe and North America looking for it.
Turns out they were looking in the
wrong hemisphere. Researchers led by
Chris Todd Hittinger of the University of
Wisconsin–Madison and Diego Libkind
of the Argentinean National Council
for Scientific and Technical Research in
Bariloche have tracked the missing wild
parent of lager yeast to the beech forests
of Patagonia. The researchers report the
capture of the newly discovered yeast,
dubbed S. eubayanus, in the Aug. 30
Proceedings of the National Academy
of Sciences.
“I got chills reading it, I was so excited,”
says Barbara Dunn, a comparative genet-
icist at Stanford who has been on the trail
of the wild yeast herself. “It is incredibly
surprising that it is from Patagonia.”
Libkind found S. eubayanus in galls —
pale peach balloonlike structures
resulting from fungal infections— on
Patagonian beech trees. The galls, full of
sugar, house S. eubayanus and another
wild yeast that ferment the sugars. It’s
generally chilly in Patagonia, just the way
lager yeast like it. Lagers are brewed at
4° to 9° Celsius (39° to 48° Fahrenheit).
The S. cerevisiae yeast used for making
ales, wines and other alcoholic beverages
don’t like the cold, preferring temperatures of about 15° to 25° C (59° to
77° F). So when Germans started brewing beers in winter to avoid summertime
contaminants such as molds and bacteria that skunk beer, the chillier brewing conditions would have favored the
creation of a hybrid lager yeast based on
S. cerevisiae and a cold-loving relative,
says evolutionary biologist Antonis Rokas
of Vanderbilt University in Nashville.
Galls— growths resulting from a fungal
infection —on beech trees in northern
Patagonia contain a wild yeast that
gave rise to a hybrid yeast used in beer.
The researchers aren’t sure how
S. eubayanus got to Bavaria; perhaps by
hitching a ride on beechwood or barrels
made of beech, or on fruit or in the belly
of a fruit fly. However it got to Europe,
when S. eubayanus arrived it found a
ready-made niche and a partner to merge
with in breweries, Rokas speculates.
Knowing the identity of the wild parent may help scientists learn how the
lager hybrids formed and how domestication genetically changed the yeast,
Rokas says. Brewers may also be able to
create new hybrid strains that can be tailored for modern brewing practices.
Butterfly masters disguise
the tasty Heliconius numata butterfly (right column) evades
predators by copying the wing patterns of a foul-tasting species,
Melinaea mneme (left column). H. numata, also known as the
passion-vine butterfly, has to get the pattern exactly right or a
sharp-eyed bird will spot the fake and gobble it up. born mimics,
members of the species lock in wing patterns with flipped-around
bits of Dna, richard ffrench-Constant of the university of exeter
in england and colleagues report online august 14 in Nature.
the flipped Dna causes six or more genes —on a section of a
chromosome important in setting wing patterns in butterflies and
peppered moths —to be inherited as a single unit, a supergene.
Different versions of the supergene allow H. numata to adopt
seven different wing patterns reminiscent of several bad-tasting
species. other Heliconius butterflies mimic only one nonpalatable
species. researchers aren’t sure if other butterfly species use
Dna flipping to determine their patterns. — Tina Hesman Saey
From top: D. LibkinD; © mathieu Joron
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