Islands of Life, Part IV

More than half a century ago, Yungay was mined for nitrates. A short walk from the campsite where scientists stay while studying the Yungay salar is a cemetery where miners and their families were buried. Credit: Henry Bortman

Astrobiology Magazine Field Research Editor Henry Bortman recently accompanied a group of researchers to the driest place in the world: Chile’s Atacama Desert. There, in an environment that resembles ancient Mars, even bacteria have a hard time surviving. In this fourth article in a series, Bortman reports on the work of two young researchers, Sergio Valea and Petr Vitek – and describes his visit to a cemetery.

Yungay salar, Atacama Desert, Chile
May 11, 2011

I spent my next to last day in the Atacama wandering around the salar at Yungay, the “headquarters” for the expedition I was accompanying. The Yungay salar is where bacteria were first discovered living inside halite (salt) rocks. Although other salars with colonized halite rocks have since been found, much of the ongoing research into how these bacteria survive such an arid environment still takes place in Yungay.

At dawn, Petr Vitek and I took a walk to a nearby cemetery, about a kilometer from the expedition campsite. Given that almost nothing can live in Yungay, it may seem an odd place for a cemetery. But more than half a century ago, Yungay was the site of mining operation that extracted nitrates for fertilizer. A small makeshift town, known as an “oficina,” existed here, where miners and their families lived. The area around the Yungay campsite is littered with old rusted cans, buttons, shoes and shards of porcelain plates and cups, an outdoor museum of sorts, displaying remnants of this earlier time. Since the invention of artificial fertilizer, nitrate is no longer mined to any great extent in the Atacama. But many cemeteries like the one at Yungay can be found throughout the desert, marking the sites of former oficinas.

Coastal fog that spreads into parts of the Atacama can be seen some mornings from Yungay, although the Yungay salar itself almost never experiences fog events. Credit: Henry Bortman
Sergio Valea examines the quality of light transmitted by a piece of colonized halite. Credit: Henry Bortman

As we walked toward the cemetery, Petr and I noticed fog off in the distance, although it burned off quickly once the sun rose. Fog rarely intrudes on the Yungay salar, but it is common on the Pacific coast, some 65 kilometers (40 miles) away, and fingers of it penetrate in places though low passes in the coastal mountain range into the core of the desert. Along with differences in rainfall, the presence or absence of fog in a particular location affects its microclimate, which in turn affects what microorganisms are able to survive there.

Before breaking off a halite rock to bring back to his laboratory for study, Petr Vitek inscribes on it an arrow pointing north to indicate the rock’s orientation in the field. Credit: Henry Bortman

The Yungay salar is a roughly triangular-shaped bowl, roughly 4 km (about 2.5 miles) long and 3 km (2 miles) wide, the remains of a lake that evaporated millions of years ago, leaving behind only salt and sand. (Click here to explore a 360-degree panoramic image of the Yungay salar.)

After breakfast, and before it got too hot, Vitek, Alfonso Davila, Sergio Valea, and I headed east to explore the Yungay salar and collect samples. You were introduced to Davila in earlier posts, so I’ll focus in this article on Valea’s and Vitek’s work.

Valea is a PhD candidate – Jacek Wierzchos, who discovered Yungay’s halite-dwelling bacteria, is one of his advisors – at the Spanish National Research Council in Madrid, Spain. Valea’s research focuses on the microhabitat inside halite knobs (which the scientists call pinnacles). During this expedition, he explained, he was looking for “pinnacles which are essentially clean of dirt and sediment, pure halite … in order to study the light-transmission properties of halite.”

Much of the focus on the environment inside the halite has centered on how the halite absorbs and retains water. That makes sense given that the near total absence of water is what makes the Atacama interesting in the first place. But the primary organism inside the halite is a photosynthetic cyanobacterium, which requires not only water but also sunlight. Valea is interested in understanding the bacteria’s specific light requirements.

A meteorological station set up in the Yungay salar monitors year-round temperature, humidity and rainfall. Credit: Henry Bortman

His research so far has shown that sunlight can penetrate more deeply into halite than previously believed. The only previous scientific paper written on the subject, Valea told me, claimed that light could penetrate only about 3 mm (about 1/8 of an inch) into halite. “But I show that it can pass through about 11 mm (about 7/16 of an inch) or more,” he said.

This may seem like splitting hairs, but for the microbes it’s a huge difference. Halite lets through light the organisms need for photosynthesis, but screens out harmful UV radiation. The more deeply inside the halite rocks the microbes can live, the less they have to worry about UV. When environmental conditions – impurities in the halite, for example – force them to live near the surface to get the light they need, they have to produce the protective pigment scytonemin to block UV radiation. The energy they use producing scytonemin could otherwise be used for growth or cell division, and organisms living on the very edge of habitability don’t have much energy to spare.

Vitek is also interested in scytonemin, but from a different angle. A post-doc researcher at Charles University in Prague, Czech Republic, Vitek uses Raman spectroscopy to hunt at the micron scale for biological molecules, such as scytonemin, inside colonized halite.

During the mid-day heat (44 C, 111 F), Davila, Vitek and Valea (l to r) relax in the shade of a human-introduced tree. Credit: Henry Bortman

Raman spectroscopy is a non-destructive technique that takes advantage of the interaction of certain chemical bonds with laser light. When laser light is beamed at a sample, “Part of the light is absorbed, part of the light is reflected, and some light is scattered,” Vitek explained. A small part of the scattered light shifts frequency, and it is this shift, the “Raman effect,” that is detected by a Raman spectroscope. Different combinations of peaks in the resulting spectral record indicate the presence in a sample of different compounds, both biological and inorganic.

Raman spectroscopy is particularly useful in detecting biological pigments because of the way those pigments interact with light. A Raman spectroscope will be part of the scientific payload planned for the European Space Agency’s ExoMars rover, which will search for evidence of past or present life on Mars.

One of our destinations during our stroll through the salar was a meteorological, or “met,” station. The met station measures and logs temperature and relative humidity both inside and outside one of the colonized halite rocks. There is also a rainfall gauge—just in case. A small antenna, mounted on a rusty tin can, periodically broadcasts the logged data via satellite.

At dusk, the gypsum outcrop at the eastern edge of the Yungay salar is bathed in golden light. Credit: Henry Bortman

We also stopped to check up on another experiment, a group of halite rocks colonized by a different species of cyanobacteria than the one found in Yungay. The rocks were collected from a salar near Iquique, roughly 380 km (about 235 miles) north of Yungay, and transplanted in Yungay to study the effect of this change in location on the microbial community inside the rocks.

By then it was mid-day and the temperature was climbing to its high of 44 degrees Celsius (111 degrees Fahrenheit). So we dragged ourselves back to our campsite where we engaged in a common afternoon desert-research activity, drinking beer in the shade.

In the late afternoon, after things had cooled off a bit, we drove out to the eastern edge of the Yungay salar to explore an outcrop of gypsum, another mineral common in the Atacama. Extensive gypsum deposits have been detected on Mars, and some scientists have suggested that these deposits would be a good place to search for evidence of past martian life.