Dried-up slime could help microbes survive briny waters on Mars

__life of brine

NASA/University of Arizona

By Leah Crane

SLIME could help microbe stowaways survive a trip to Mars– and thrive in the planet’s salty waters once they arrive. Biofilms, colonies of cells embedded in a gooey protective coating, live longer than single cells when exposed to Mars-like brines – and even longer when they are dried out first, as they would be after travelling through space.

Biofilms are everywhere on Earth, from dental plaque and pond scum to the systems used to clean up oil spills. They also protect microbes from antibiotics, radiation, temperature changes and other extreme conditions that would otherwise kill them immediately.

But we are only just beginning to figure out how biofilms react to alien environments – which is crucial if we are to avoid contaminating other worlds.

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Although Mars is mostly dry, we know its ice caps contain water, and the planet may even have seasonal streams. To examine how biofilms might react to these Martian waters, Adam Stevens at the University of Edinburgh, UK, and his colleagues dunked them in seven Mars-like brines that had a range of different dissolved salts and strengths.

“Martian waters are the most likely spots to find __life but also the best places for contaminants to thrive”

In the weakest brines, all of the biofilms thrived, lasting well past the 5-hour observation time. As the brines became harsher, though, a divide started to appear: biofilms that were dried out prior to dunking did better than those that remained hydrated.

Any biofilms that made it from Earth to Mars would probably be desiccated from the trip. It turns out that this arduous ride could prepare them to thrive on Mars.

After a momentary shock in the most intense brines – which were about 70 times saltier than the weakest – dessicated biofilms started to grow. This may have been a consequence of communication throughout the biofilm: a cell on the outside edge of the film, exposed to Mars’s brutally salty brines, could send a warning signal to the insulated cells deeper down. Those cells could either form more goo or reproduce more quickly to build their barrier.

After 5 hours in the harshest brines, all the microbes in the dried-out biofilms were dead. But the hydrated biofilms fared far worse: their cells died within an hour and some were done for in less than half an hour (bioRxiv, doi.org/bxnc).

On Mars, areas with water (even salty, briny water) are designated as “special regions” by the international Committee on Space Research. They are the most likely spots to find Martian life, but also the best places for Earth-based contaminants to thrive.

Biofilms could help Martian microbes survive, so they might be something to look for in Mars’s briny recurring slope lineae or in the salty seas of icy moons further out in our solar system. But the danger is that they could also help microbes from Earth thrive, overtaking any previous life and polluting the science.

“This research gives us some information about what we could possibly look for if we do go and investigate these brines – which, on the flip side, we’re saying maybe we shouldn’t,” says Stevens.

“To me, this is a kind of a call to pick up the baton of this area that we really need to understand as we launch into an era of space travel,” says Jennifer Macalady at Penn State University in University Park.

This article appeared in print under the headline “Slimy bacteria may thrive in Mars brine”