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Looking through the desolate landscape of Valle de la Luna, the idea seems to go against the intuition.
What is the world's driest desert, home to some of the most extreme ultraviolet radiation levels on the planet, could have to do with fighting the disease? But as Michael Goodfellow, a microbiologist at Newcastle University explained, the inhospitality of the Atacama Desert is precisely what could make it useful.
"The principle was that, because conditions are very difficult in the Atacama Desert, the organisms adapt to it," he explains. Goodfellow hoped that if the bacteria had survived in such a hostile environment, they could probably produce new chemical structures that could have important medical applications.
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In 2008, he received a soil sample taken from the desert hyperarid core, parts of which have not been subjected to rain for millions of years and were once considered to have exceeded the drought limit. "Frankly, we did not expect to isolate anything," admits Goodfellow. But to his surprise, he was able to develop a diverse population of bacteria from the sample, initiating a decade of research on the microbial fauna of the desert.
This is the type of bacteria living in Atacama that has proved particularly interesting: a phylum-producing phylum called actinobacteria. In the world of microbiology, actinobacteria are renowned for their ability to secrete organic chemicals called secondary metabolites, which help them to defend against rival microbes.
Take streptomyces griseus, for example, a species of actinobacteria that you might find in a handful of garden soil. A sample of Streptomyces, placed in a colony of Mycobacterium tuberculosiswill release a chemical that prevents its bacterial neighbors from growing the protein they need to survive. When scientists from Rutgers University managed to isolate this chemical in 1944, they came across the first antibiotic treatment of tuberculosis, thus saving countless lives.
In total, 46 new molecules have been isolated from Atacama bacteria up to now, many of which have antibiotic, antiviral or anticancer properties.
The new species of desert actinobacteria studied by Goodfellow and others have proved to be competent chemists. A 2018 review identified a total of 46 new molecules isolated to date among Atacama strains, many of which have antibiotic, antiviral or anticancer properties. Although Goodfellow points out that there is still no solid drug, the results show that the desert is a promising place for antibiotic research.
Life on the edge
The Atacama is an excellent example of what scientists have dubbed "the extremobiosphère" – regions of the world where factors such as high aridity, UV radiation, pH or pressure have pushed life to the limit. Recent years have seen researchers travel the globe to find increasingly hostile habitats, where they have consistently found robust colonies of surviving bacteria.
In 1998, a Japanese submarine brought barophilic bacteria from sediments of the Marianas Trench to 11,000 m below sea level. These bacteria are capable of developing at pressures 700 times higher than those of the sea. area. In 2009, geomicrobiologist Jill Mikucki announced the discovery of a population of microbes living under 400 m of Antarctic ice, which have survived for millions of years exploiting the energy of iron deposits. . Whether they live on a freshly erected Icelandic volcano or dormant for millennia in Siberian permafrost, the bacteria have truly colonized the world.
This body of exploratory research has redefined our understanding of the limits of life by teaching us the ingenious ways in which bacteria have evolved to tolerate their environment. But perhaps it is the imminent specter of antibiotic resistance that is the most pressing reason for exploring extreme ecosystems.
The superbugs – pathogens that have learned to get rid of our antibiotic attacks – are already responsible for hundreds of thousands of deaths each year worldwide. The World Health Organization describes them as "one of the greatest threats to global health, food security and development today." Worse, by the time our most reliable drugs began to fail, the late twentieth century saw the development of new antibiotics be delayed.
bioprospecting
Public health organizations around the world are encouraging doctors, patients and farmers to use antibiotics responsibly to help stop the spread of superbugs, but there is consensus on the need for new drugs. Sometimes a potentially useful chemical can be found right in front of our nose. In 2016, German researchers discovered an antibiotic previously unknown in a human nostril, capable of killing drug-resistant Staphylococcus aureus, also called MRSA. In other cases, fully synthetic molecules may prove to be successful antibiotics.
But many scientists argue that we should also explore the natural world in search of a new biochemistry, an approach known as "bioprospecting." Marcel Jaspars, a chemist specializing in natural products at Aberdeen University, is one of these lawyers. "70% to 75% of all antibiotics come from nature," he notes. "It seems to me that we should look more deeply at how nature makes these molecules and how we can actually find antibiotic compounds."
And these are extreme, seemingly lifeless places, like Atacama, that seem to be the most promising places to find new weapons in the fight against antibiotic resistance. Advances in genetic sequencing have shown that the dry valleys of Antarctica, whose cold, arid soil is considered unique in the world, harbor a much greater diversity of actinobacteria than previously thought. before. The exploration of the deepest ocean trenches has led to the discovery of a whole new class of chemicals, called "abyssomicines", in the honor of the depths where their bacterial creators have been discovered. From the sand dunes of Merzouga in southern Morocco to the deserts of Badain Jaran and Tengger in China, microbiologists around the world are building an ever-growing library of compounds with bioactive properties.
It should be noted that many molecules extracted from these extreme bacteria will probably never become drugs. For every antibiotic that changes the world, like penicillin, scientists have uncovered countless chemical compounds that are either too toxic or simply not efficient enough to be medically useful.
Their tolerance to UV rays could prove useful in the cosmetics industry as it looks for ways to protect human skin from damage from sunlight.
But according to Chilean microbiologist Cristina Dorador, Atacama's microbiome expert, there are many other reasons why we should value her unseen research topics. The ability of desert bacteria to withstand high aridity and salinity could help plants to grow in poor conditions, she says. And their tolerance to UV rays could prove useful in the cosmetics industry as it looks for ways to protect human skin from the damage caused by sunlight.
The researchers also described the potential of the bacterium as an industrial biocatalyst. Dorador suggests that their ability to metabolize inorganic material could be used in the copper mining sector of Atacama, which constitutes the pivot of the Chilean economy. According to her, the adaptation of bacteria to their desert environment could make them particularly suitable for facilitating the extraction process.
And the researchers may have only touched the surface of Atacama's potential. It is estimated that only about 1% of all microorganisms in the natural world have been isolated and cultivated (laboratory-grown), but new genetic sequencing techniques are helping researchers like Dorador get an idea of what exists elsewhere.
"We know that they are there, that we have great microbial diversity, but we do not really know what their effects are, nor their potential," she says. "There is really a whole microbial universe to discover in the Atacama desert."
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