Salt-Loving Microbe Grows in Mars-Like Conditions
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- Adam Robinson at the University of Florida and colleagues showed that Haloferax volcanii, an archaeon from the Dead Sea, actively grew over 160 days in water with 225 grams of salt per litre, at 21°C and 24 millibar pressure, with perchlorates and nitrates added — the first demonstration of growth rather than mere survival for a salt-loving extremophile in Mars-like conditions
- Robinson noted the growth medium became cloudier and perchlorate was biologically reduced, with scanning electron microscopy revealing extensive biofilm formation, calling it 'pretty robust evidence that points towards active growth and not just survival'
- Robinson acknowledged two key caveats: the experiment used yeast extract as a carbon source, which 'would not be found on Mars today,' and the 24-millibar pressure may exceed what is actually found on Mars, where surface pressure is 6–12 millibar
- Sean McMahon at the University of Edinburgh countered that at Mars's real surface pressure of 6–12 millibar, liquid water cannot exist, and below the surface where 24 millibar is reached, temperatures are well below freezing — so no liquid water, no life
- Robinson's team is already running follow-up tests with cold-loving halophiles at 0–4°C and 7–12 millibar, plans to swap yeast extract for acetate (a carbon source thought to exist on Mars today), and intends to test salt-loving methanogens that could feed on atmospheric CO2 — methane having already been detected on Mars
- Robinson noted that since the 1976 Viking missions, subsequent Mars missions have deliberately avoided the most potentially habitable sites to avoid contaminating them with Earth microbes
Why it matters: Past Mars simulation studies showed microbes could only survive, not grow, in those conditions — Robinson's team crossed that threshold with a salt-loving archaeon, but Edinburgh's McMahon flagged that the tested pressure still exceeds the 6–12 millibar found on the actual Martian surface, where liquid water cannot exist. The result narrows but does not close the gap between Earth extremophile capability and the real Martian environment.
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