Microorganisms adapted to salty and cold environments help to understand the habitability of Mars


Mosaic of images taken by the Mastcam aboard the Curiosity rover during the 520th sun, or Martian day, of the mission (September 28, 2012). Analysis of the collected samples found the presence of perchlorates. Credits: NASA/JPL-Caltech/MSSS.

A team of researchers from the Center for Astrobiology (CAB, CSIC-INTA) has studied the ability of some microorganisms to adapt to salty and cold environments by using molecules capable of controlling the freezing process. The results show a close environmental-microorganism relationship that opens up a novel path of astrobiological research on the habitability of icy brines on Mars.

Extremophilic microorganisms are a fundamental tool to understand how life has made its way on Earth and also for the study of habitability outside our planet. Within the wide variety of extremophilic organisms, the most interesting are the so-called polyextremophiles, those organisms capable of surviving in environments that present several extreme conditions simultaneously, for example, environments with low temperatures (psychophilic) and high salt content (halophiles). These conditions, precisely, occur in some regions of Mars such as the Gale crater, where the presence of a type of specially hygroscopic (water-absorbing) and caanthropic (water-absorbing) salts (which destabilize water molecules and other macromolecules of cells, causing them to break up) has been detected: perchlorates, with magnesium perchlorate being predominant. This similarity in the conditions of both environments makes the study of terrestrial organisms particularly relevant, because of the important astrobiological implications and the habitability of Martian environments.

A recent study, conducted by a team of researchers from the Center for Astrobiology (CAB) and published in the journal Astrobiology, has examined, in particular, the medium-bacterial interaction for these low temperature and high salinity conditions, using a halotolerant and psychophilic microorganism, the bacterium Rhodococcus sp. JG3, capable of surviving high salt concentrations and sub-zero temperatures.

This microorganism could, as is known to many psychophiles and, specifically, other bacteria of the same genus, dispose in their molecular machinery of so-called ice binding proteins (IBPs) to adapt to freezing conditions. These proteins have the ability to bind to the ice to modify their crystalline configuration and thus control the freezing process, promoting it (InP) or blocking it (Antifreeze Proteins, AFP), so that they vary the temperature at which the water changes phase. This is a huge adaptability and provides advantageous situations such as the creation of microenvironments around the cell with liquid water available at sub-zero temperatures, thus increasing its survival window.

As Laura García Descalzo points out, CAB researcher and lead author of the study, "the first results obtained, although preliminary, raise interesting questions that could open up new avenues of research in Astrobiology: the study of how adaptations, at the molecular level, that extremophilic organisms develop to survive environmental conditions could, in turn, influence those same conditions, so that their own survival depends, in large part, on the microorganism-environmental interaction".

For García Descalzo, the study "represents the beginning of a novel research pathway on the habitability of frozen brines on Mars, which involves studying the potential role of microorganisms and their molecular adaptations in solutions of perchlorates at sub-zero temperatures for their own survival, being able to modulate, in turn, the medium in which they survive thanks, among other things, to the role of proteins as interesting as IBPs".

The identification of molecules used by microorganisms to adapt to environmental conditions is also a valuable source of information that can be used as a "marker" of the presence of life.


Fuente: UCC-CAB

Fecha: 2020-08-26


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