Dried Earth microbes could grow on Mars with just a little humidity

SAN FRANCISCO — Salt-loving microbes can dry out and come back to life with just a little humidity, researchers have demonstrated for the first time.

Scientists have suspected that microbes in arid places may get their moisture from humidity alone, but no one has shown that dried-out microbes can revive with water sucked from the air. Dessicated Halomonas bacteria from Washington’s Hot Lake perked up and began growing again after absorbing humidity in a jar, astrobiologist Mark Schneegurt, of Wichita State University in Kansas, said June 21 at the ASM Microbe 2019 meeting. That discovery has implications for the search for life on other planets, and for preventing life from Earth from contaminating other worlds (SN: 1/20/18, p. 22).

Schneegurt and colleagues grew Halomonas bacteria in magnesium sulfate brines. Magnesium sulfate (also called Epsom salts) and perchlorates are the main types of salts found on Mars. Those salts don’t play keep-away with water molecules the way sodium salts do, so microbes have a better chance of snagging some moisture.

Magnesium salt–tolerant microbes have been detected in clean rooms where NASA builds its spacecraft, Schneegurt said. “There’s definitely life on Mars. It just came from Earth,” he said. The question is “how worried do we have to be that an organism from Earth can survive and grow there?”

Halomonas growing in magnesium brines at room temperature double their numbers in three to four days, the researchers found. Even at –4° Celsius — a more Mars-like temperature — the microbes grow, but it takes months. The microbes also held up well to repeated cycles of drying and wetting.  “We lose a few, but not an enormous amount,” he said.

Mars currently is probably too cold and dry for Earth microbes to thrive there, Schneegurt said. But “at least some of them can grow in the chemical conditions there.”