The Dry Valleys of Antarctica (flickr/Imira)
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.
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