Florida team grows Haloferax volcanii for 160 days under simulated Martian subsurface conditions

Researchers led by Adam Robinson at the University of Florida grew the salt-loving archaeon Haloferax volcanii in the laboratory under conditions meant to resemble the shallow Martian subsurface, according to a University of Florida release on EurekAlert. The cultures grew over months at a fraction of Earth's normal atmospheric pressure, in a solution 7 times saltier than seawater, using chemicals similar to bleach for respiration eurekalert.orgEurekAlerteurekalert.orgOpen source ↗. The study was published on Nov. 5 in Applied and Environmental Microbiology. It was co-led by Scott Perl of the Los Angeles Natural History Museum and the Blue Marble Space Institute of Science.

Experiment design

Haloferax volcanii is an extremophile that tolerates extreme conditions on Earth. The team chose it for its preference for high-salt environments, similar to those in the shallow Martian subsurface eurekalert.orgEurekAlerteurekalert.orgOpen source ↗. Earlier work applied single stresses, such as high salt or low pressure, or tested whether organisms stay alive under several harsh conditions at once, often for only hours or days.

Here the cultures were kept for 160 days in oxygen-free, carbon dioxide-rich conditions. They were given nitrate or perchlorate, which they could use in place of oxygen during respiration. Cultures given neither compound remained viable but showed no measurable growth, which let the authors separate survival from reproduction eurekalert.orgEurekAlerteurekalert.orgOpen source ↗. With either compound the microbes reproduced and used it to sustain metabolism, although growth was substantially slower than in comparable cultures at Earth's atmospheric pressure.

The low-pressure cultures also formed dense biofilms. The authors say the films may have helped hold water in the salty solution, since the cultures lost little of their water during the experiment.

Limits of the simulation

The laboratory did not reproduce every Martian condition. The cultures were held at 70 degrees Fahrenheit, while most of the Martian subsurface is far colder. They also received nutrients supplied by the researchers, and the liquid-water pockets the setup resembles have not been confirmed on Mars. "The environment that we're mimicking in this experiment has not been observed on Mars, but is theorized to exist," Robinson said eurekalert.orgEurekAlerteurekalert.orgOpen source ↗.

The results do not establish that life exists on Mars today. According to the authors, they suggest that future subsurface missions should consider whether some environments could support active life, not only evidence of life that existed billions of years ago. Perl noted that any Martian microbes would have had billions of years to adapt to the planet's changing conditions. The authors add that the approach could help design life-detection experiments and reduce the risk of carrying Earth microbes to Mars aboard spacecraft eurekalert.orgEurekAlerteurekalert.orgOpen source ↗.