A treasure hunt for microbes in Chile’s Atacama desert

From Knowable Magazine,

By Lindzi Wessel,

Edited by - Amal Udawatta,

                 The Atacama Desert, one of the driest places on Earth, has become an unexpected source of microbes that                                                                                         thrive in extreme environments. (CREDIT: PHOTO BY JARED VERDI                                                                                       ON UNSPLASH

Benito Gómez-Silva is surrounded by nothing. For as far as the eye can see, no plants dot the landscape; no animals amble across the salt-crusted soil that stretches out to the base of distant mountains. Besides some weak wisps of clouds inching slowly past a blazing sun, nothing moves here. The scenery consists exclusively of dirt and rocks.

It’s easy to imagine why Charles Darwin, peering across a nearby expanse of emptiness 187 years ago, proclaimed this region — the Atacama Desert in northern Chile — a place “where nothing can exist.” Indeed, though scattered sources of water support some plant and animal life, for more than a century most scientists accepted Darwin’s conclusion that here in the Atacama’s driest section, called the hyper-arid core, even the most resilient life forms couldn’t last long.

But Darwin was wrong and that’s why Gómez-Silva is here.

Rising before dawn to beat the day’s most brutal heat, we’ve driven for an hour along an increasingly deserted road, watching the terrain grow steadily emptier of plants and human-built structures. After heading south along Chile’s Coast Mountain range, we turn inland towards the Atacama’s heart. Here the University of Antofagasta desert microbiologist will search for a microscopic fungus that he hopes to isolate and grow in his lab.

We’re at the driest non-polar place on Earth, but Gómez-Silva knows there’s water here, hiding in the salt rocks around us. Just like the salt in a kitchen shaker will soak up water in humid weather, the salt rocks absorb tiny amounts of moisture blown in as night-time ocean fog. Then, sometimes for just a few hours, microscopic drops of water coalesce in the nanopores of the salt creating “tiny swimming pools,” Gómez-Silva says — lifelines for microbes that find refuge in the rocks. When moisture and sunlight coincide, these microbial fungi start to photosynthesize and grow their communities, seen as thin, dark lines across the faces of their salt-rock homes. With the gentle tap of the back of a hammer, Gómez-Silva dislodges a few small rocks with particularly prominent markings. They will head to his lab, where his team will break them down and try to extract the microbes inside and keep them alive in laboratory dishes.

Gómez-Silva is part of a small but strong contingency of scientists searching for living microbes here in the world’s oldest desert, a place that’s been dry since the late Jurassic dinosaurs roamed Earth some 150 million years ago. Anything trying to survive here has a host of challenges to contend with beyond the lack of water: intense solar radiation, high concentrations of noxious chemicals and key nutrients in scarce supply. Yet even so, unusual and tiny things do  grow, and researchers like Gómez-Silva say that scientists have a lot to learn from them.

Part of unlocking those secrets involves changing the world’s view of the Atacama, he says, a region that historically has been valued for mining precious minerals above all else. Coauthor of a 2016 Annual Review of Microbiology  paper on the desert’s microbial resources, Gómez-Silva is one of several researchers who believe that the Atacama should be prized for something altogether different: as a place to characterize unknown life forms. Describing such extremophiles — so named because of their ability to thrive in extreme, almost otherworldly conditions — has the potential to develop new tools in biotechnology, to answer questions about the very origins of life and to guide us on how to look for life on other planets.

“For centuries the Atacama was ‘lifeless,’” Gómez-Silva says. “We need to change this concept of the Atacama … because it’s full of microbial life. You just need to know where to look.” 

Extreme conditions

The Atacama stretches some 600 miles along the coast of South America — its borders aren’t precise — and is flanked on the east by the volcanic Altiplano of the Andes Mountain range and to the west by Chile’s Pacific shores. Roughly the size of Cuba, the desert is as varied as it is hostile.

Yet, despite the desolation, scattered treasures attract visitors from around the world. Near the town of San Pedro, about 150 miles to the east of Gómez-Silva’s university, tourists make trips to see the Atacama’s strange moonlike valleys, the lagunas that serve as oases for migrating flamingos and Chile’s El Tatio geyser field. The desert includes a series of plateaus, ranging in elevation from around sea level to more than 11,000 feet, making it one of the highest deserts in the world. Various international observatories take advantage of that altitude and the desert’s record-low moisture to snap clear pictures of the stars.

Several factors contribute to the Atacama’s extreme dryness. Moisture from prevailing southeast trade winds hits the Andes and condenses as rain on their eastern (non-desert) side. Moisture in any descending warm air evaporates before becoming rain due to high air pressure. And to the west, the cold waters of the Pacific Ocean’s Humboldt Current chill the air so it can’t carry much water vapor.

The Atacama’s harsh conditions are thanks to the features that mark its borders. Storm fronts moving in from the east rarely breach the towering peaks of the Andes mountains and a thick current of cold ocean waters moving up from Antarctica chills the air along Chile’s coastline, hampering its ability to carry moisture inland. Many parts of this desert receive mere millimeters of rain each year, if any at all. The Atacama Desert city of Arica, just below Peru’s border, holds the record for the world’s longest dry spell — researchers believe not a single drop of rain fell within its borders for more than 14 years in the early 1900s.

Without water, little should survive: Cells shrivel, proteins disintegrate and cellular components can’t move about. The atmosphere at the desert’s high altitudes does little to block the sun’s damaging rays. And the lack of flowing water leaves precious metals in place for mining companies, but means distribution of nutrients through the ecosystem is limited, as is the dilution of toxic compounds. Where water bodies do exist in the desert — often in the form of seasonal basins fed by subterranean rivers — they frequently have high concentrations of salts, metals and elements, including arsenic, that are toxic to many cells. Desert plants and animals that manage to make it in the region typically cling to the desert’s outskirts or to scattered fog oases, which are periodically quenched by dense marine fogs called camanchacas. 

Seeing such conditions on an 1850s expedition to the Atacama at the behest of the Chilean government, even German-Chilean naturalist Rodulfo Philippi, who first documented many of the plants and animals that live in the less extreme parts of the Atacama, emphasized that the desert’s value lay in mineral mining, even as he lamented the challenges of unearthing it due to the region’s desolation.