The Dry Valleys of Antarctica don’t sound like a particularly hospitable
place: sub-zero temperatures, salty soil, and less than 10 centimeters
of water per year (mostly in the form of snow that sublimates upon
groundfall). The region has earned its reputation as the coldest,
driest desert on the planet.
Which is why a recent study by Charles Lee and his group at New
Zealand’s University of Waikato is particularly surprising. In the most
recent ISME Journal, the team not only shows that microbes are
scattered around the valleys, but that their populations are
surprisingly diverse. It’s not just a few hardy species eking out a
precarious existence at the bottom of the world.
At first glance, the Antarctic interior seemed to be lifeless; Robert
Falcon Scott suspected as much in his 1905 “The Voyage of the
Discovery”. Decades later, biologist Imre Friedmann was exploring the
Dry Valleys – an ice-free region in the Antarctic interior – and
something in the rocks caught his eye. It was a green layer, just
beneath the surface, an unexpected contrast to the drab glacial till
that covered the valley. It turned out to be chlorophyll, the molecular
Forex bureau that facilitates the transfer between the light and
chemical forms of energetic currency. Friedmann showed that life was in
fact possible in the frigid desert – it just had to retreat from the
surface and tap into the water supplies of rock and soil pore spaces.
More recently, the Antarctic Dry Valleys have become a popular
astrobiological analog site, arguably the closest thing in temperature
and climate to places like Mars. Almost every Mars lander instrument
destined for the launch pads of Cape Canaveral is put through its paces
in Antarctica.
Extreme environments are also useful testing grounds for ecologists
hoping to understand how microbes access energy and interact with each
other and their environment. That’s what Lee and his team thought, at
least. But if the idea is to test drive an ecological theory in
“simple” microbial communities, it becomes difficult when such places
turn out to be much more complicated than you had hoped.
Lee surveyed four different valleys, sequencing as many pieces of a
certain region of the bacterial 16s rRNA gene that he could get his
latex-gloved hands on. 214 distinct species popped out: this was
certainly no bare bones microbial community. (It’s also worth noting
that the group only examined the Bacteria – microbes of the Archaeal
domain of life are almost certainly present and would contribute an
additional jolt of diversity.)
But what Lee found next really surprised him: when he compared the lists
of species, there was almost no overlap. Only two of the 214 species
were found in all four valleys. All of the sites could support life,
but each seemed particularly picky in its own way.
This discovery flouts the previous party line that microbial species in
the Dry Valleys were transported primarily by wind, ensuring a pervasive
population of “cosmopolitan” species. Rather, specific geochemical
differences – like copper, magnesium, or salt concentrations – cause the
most significant variation. It seems likely that a common set of
microbes can be dispersed by the constant Antarctic wind, but that a
subset of organisms is selected for by geochemical pressures. The four
Dry Valleys may look and feel similar, but on the microscale, even
subtle chemical shifts change a microbe’s worldview.
The microbial dependence on geochemistry looms large given the wholesale
environmental changes taking place around the world, changes that have
accelerated in recent years as the scope and scale of anthropogenic
effects broaden. And while the Dry Valleys might not qualify as a
“simple” ecosystem, it’s still a lot less chaotic than your average rain
forest, lake bottom, or farm soil. If we want to have any hope of
figuring out what’s going on in those places, the opposite end of the
planet seems like a good place to start.
0 comments:
Post a Comment