Winter wonderland
S
HAWN BROWN’S field trip got off to a
bad start when he discovered that his
experiment had disappeared. He had
travelled thousands of kilometres from the
University of Memphis to Finland to study
blood-red snow algae when a heatwave
had turned his plans to mush. The sun had
melted the dark red living patches, and now
only white snow remained.
With funders to satisfy, Brown and his
team struck on a Plan B: look for algae in
the pristine white snow. They didn’t expect
to find much, but to their surprise they
discovered a rich hidden ecosystem of algae,
fungi and bacteria. “I was just blown away
by the biodiversity,” says Brown.
Until recently, microbes in snow were
assumed to be rare and largely inactive.
It is only in the past couple of years that
scientists, including Brown, have used
state-of-the-art DNA sequencing technology
to reveal the secret life hidden there. As we
learn more, it is becoming apparent that this
is no mere curiosity: snow microbes play a
role in cycling nutrients and carbon. They may
be tiny but, given that snow covers a third of
land on Earth, they could have an overlooked
impact on the planet’s health and climate.It may seem improbable that life could
survive among ice crystals, given its
dependence on liquid water, but microbes have
evolved ingenious ways of eking out a living
in snow. They grow in watery veins that run
through the snow pack, melted either by
impurities or by proteins that the microbes
make. In extremely cold environments, some
microbes slow their metabolisms to such a
crawl that they can take hundreds of years to
divide. Others might just tick over in snow
then become active during a thaw. “We’re just
guessing at this point,” says Brown. “We don’t
really know how they are making a living.”
We are starting to understand where they
come from, though. Some simply fall from the
sky, swept up from Earth’s surface and carriedon winds to new destinations. Some create the
snow itself, acting as seeding points in clouds
on which freezing water can take hold and
grow into snowflakes. Others may simply lie
low in the soil, biding their time, says Brown.
Then a blanket of snow triggers a fleeting,
invisible blossoming of specialist microbes,
just as grass seeds in a desert briefly spring into
life when the rains come. Even freshly fallen
snow in your back garden has life lurking in it.
To explore the composition of these
frigid ecosystems, Brown and his colleagues
collected snow from different latitudes in
Finland, Norway and Sweden, as well as in
Colorado, and applied a technique called next-
generation DNA sequencing, which let them
study the organisms present without having to
grow them, by looking at microbial genes in
each sample. They found intriguing differences
among the various types of microbe. Bacteria
were pretty much the same everywhere in
Europe although different from the US, but
fungal species tended to stick to their own
neighbourhoods. This makes sense because
bacteria are much smaller than fungi, and soIt may appear cold and empty, but snow is teeming
with life. Claire Ainsworth dives in for a closer look
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70 | New Scientist | 21/28 December 2019“ Even freshly fallen
snow in your back
garden has life
lurking in it”