This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new experiment reveals that Earth's microbes can grow in harsh conditions similar to what may exist just below the surface of Mars, suggesting new directions in the search for potential cellular life on the red planet. The microbes grew over months in just a fraction of Earth's normal atmospheric pressure, in a solution seven times saltier than seawater, while breathing chemicals similar to bleach.
The study, led by University of Florida researcher Adam Robinson, tested whether a salt-loving microorganism could do more than survive several of the stresses associated with Mars. These include stresses that would exist on the surface and potentially in the subsurface. The microbe could reproduce and use chemicals in its surroundings to sustain its metabolism, although growth was substantially slower than in comparable cultures kept at Earth's atmospheric pressure.
The scientists focused on Haloferax volcanii, a microbe known as an extremophile for its ability to tolerate extreme conditions here on Earth. They chose Haloferax because of its known preference for high-salt environments, similar to those found in the shallow Martian subsurface. The team, which was co-led by Scott Perl of the Los Angeles Natural History Museum and the Blue Marble Space Institute of Science, published its findings Nov. 5 in the journal Applied and Environmental Microbiology.
Past experiments have attempted to answer similar questions. Researchers have grown Earth microbes under individual stresses associated with Mars, including high salt concentrations or low pressure. Other studies have tested whether organisms remain alive after exposure to several harsh conditions at once, often for only hours or days.
"Far fewer have been able to combine these conditions together and show that microorganisms can actively grow," Robinson said. For this experiment, the team kept cultures of Haloferax in oxygen-free, carbon dioxide-rich conditions for 160 days. The microbes were given nitrate or perchlorate, compounds relevant to Mars that they could use in place of oxygen during respiration.
Cultures supplied with neither chemical remained viable but showed no measurable growth, helping the scientists distinguish survival from reproduction. Observing microbial processes under these conditions can help scientists distinguish between potential biosignatures from extinct cells and biological processes from living (extant) cells. The researchers also observed dense structures called biofilms in the growing low-pressure cultures.
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