New genes for resistance to ultraviolet radiation and perchlorates discovered


Ojos de Campo, Salar de Antofalla, in the Andean highlands of Argentina. Credit: Luis Ahumada.

A scientific team, led by the Centro de Astrobiología (CAB), has discovered five new genes for resistance to ultraviolet radiation and perchlorates from microorganisms exposed to high doses of radiation. To this end, the researchers have analyzed environmental samples of hypersaline lagoons in the Andean highlands of Argentina and the salt flats of Es Trenc, in Mallorca. This finding will help scientists better understand how life adapts to extreme environments on our planet and whether it could occur on other planets or icy moons in the Solar System.

Trying to understand the origin of life on Earth and explore the possibility of it existing outside it is one of the challenges of astrobiology. A first step to this is to know the limits of that life, for which scientists resort to the so-called extreme environments we find on our planet. These environments are characterized by being, apparently, inhospium places for life. However, numerous research has shown that life makes its way through places as extreme as the icy surface of Antarctica, the hyper-arid heart of the Atacama Desert, the acidic waters of Rio Tinto (Huelva), or hypersaline lagoons and exposed to high doses of ultraviolet radiation from the Andean highlands of Argentina.

A recent study, led by the Centro de Astrobiología, has identified five new genes involved in resistance to this ultraviolet radiation. To do this, the researchers selected environmental samples of microorganisms that inhabit the hypersaline lagoons of the Andean highlands of Argentina, such as Lago Seco, at 3,200 m above sea level, and Laguna Diamante, at 4,589 m. The Salinas de Es Trenc in Mallorca were also studied, which, despite being at sea level, are home to microorganisms that resist high doses of radiation.

As reflected in the study, published in the journal Frontiers in Microbiology, researchers have discovered five genes that confer resistance to UV radiation and also perchlorate. In addition, "they also have a resistance to the compound nitroquinoline, which mimics the effect of radiation on DNA", says Eduardo González Pastor, researcher at the Centro de Astrobiología and lead author of the study. "Resistance to this compound indicates that the identified genes could be involved in repairing and/or protecting DNA damage caused by UV radiation and perchlorate," he adds. 

Researchers have used an independent culture technique to look for these radiation resistance genes. This means that it has not been necessary to cultivate or isolate microorganisms from the environments studied. "This has been done because a large part of the microorganisms cannot be grown under laboratory conditions," explains Eduardo González Pastor. Thus, the technique used has been the so-called 'functional metagenomics', which consists of isolating the DNA (which is called a metagenome) from all microorganisms in a sample, then fragmenting it and introducing it into vectors that allow genes to be expressed in a bacteria that can be manipulated in the laboratory: Escherichia coli. In this way, so-called metagenomic libraries are generated, in which each cell of E. coli would contain a fragment of the metagenomic DNA. Subsequently, the researchers exposed these libraries to UVB radiation and selected those bacteria that had radiation resistance sequenced into an environmental DNA fragment that carried and analyzed and studied the genes responsible for that resistance.

Astrobiological implications

In planetary exploration, this study could serve to lay the foundations for the generation of plants and microorganisms, necessary for life support systems outside our planet, that were more resistant to radiation, one of the main problems of space and planets like Mars.

On the other hand, the presence of perchlorate salts in soils has been identified on the red planet. "Perchlorate is an oxidizing and highly toxic agent, which would limit the use of Mars soils as substrates for crops," explains González Pastor. "This work identifies for the first time genes related to perchlorate resistance, so using these genes could modify plants to be more resistant to perchlorate, as well as plant growth-promoting microorganisms, which would promote their development in these soils," he adds.

In addition, in a climate change scenario, an increase in UVB radiation is expected to reach the Earth's surface. This may cause crop damage as they are not adapted to high doses of radiation. Therefore, "it is possible to improve the tolerance to UVB radiation of plants of food interest by modifying them with genes from microorganisms exposed to higher doses of radiation and that have developed more effective molecular resistance mechanisms", explains Eduardo González Pastor.


Fuente: UCC-CAB

Fecha: 2020-03-27


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