Dead Sea microbe grew and reproduced in Mars-like conditions

Researchers at the University of Florida have grown a microbe under a combination of Martian hazards and watched it feed and reproduce for half a year. The organism, Haloferax volcanii, is a salt-loving archaeon found in the Dead Sea and Utah's Great Salt Lake. The study, led by Adam Robinson and published in Applied and Environmental Microbiology, held the microbe in a solution seven times saltier than seawater, with almost no oxygen and a carbon dioxide atmosphere at a small fraction of Earth's pressure.

Each of those hazards has been tested alone before, and some earlier work showed microbes clinging on for months under several at once. What distinguishes this experiment, Robinson says, is the combination with active growth. Cultures offered nitrates or perchlorates — chemicals present on Mars that can substitute for oxygen — fed and reproduced. Cultures offered neither showed no noticeable growth. A preprint on bioRxiv describes the run in detail: 160 days at no more than 24 millibars of pressure, a 99.9 percent carbon dioxide atmosphere and 21 degrees Celsius, with growth in every low-pressure treatment, measured by rising optical density and by the microbes breaking down nitrate and perchlorate. The preprint calls it the first demonstration of a halophilic archaeon growing under that combination of conditions. Colonies grew far more slowly than they would on Earth, formed biofilms — clumps encased in a slimy protective layer — and lost less than four percent of their water over the months.

Robinson is careful about what this does not show. "I would not say this study suggests there is definitely life on Mars today," he said, while adding that the work supports a growing body of evidence that the planet's shallow subsurface may still retain conditions conducive to active metabolism and extant life. The lab did not reproduce every danger Martian life would face — cold, salt, radiation and thin air all strike at once — and Robinson notes that if Mars once hosted life, organisms may have evolved to tolerate increasingly hostile conditions as the planet changed.

The choice of organism carries its own weight: Haloferax volcanii serves as a standard stand-in for life that could survive on other planets. An Earth microbe that grows on perchlorates at a fraction of terrestrial pressure speaks to two questions at once — whether Mars could hold life, and what Earth's landers might deliver to it.

Robinson's closing question widens the frame: if life from Earth can grow under hostile conditions it has never naturally encountered, what might life on Mars look like after billions of years of evolution under those conditions?