An Earth Microbe Can Grow in Simulated Mars Conditions

A team led by University of Florida microbiologist Adam Robinson cultivated Haloferax volcanii, an archaeon native to Earth's Dead Sea and salt pans, for 160 days under conditions designed to mimic the shallow Martian subsurface. The experiment, published November 5 in Applied and Environmental Microbiology, combined multiple Mars-relevant stresses at once: atmospheric pressure a fraction of Earth's, a brine seven times saltier than seawater, an oxygen-free, carbon-dioxide-rich atmosphere, and the presence of nitrate and perchlorate salts detected by NASA's Curiosity and Phoenix rovers. The microbes not only survived but actively reproduced, using nitrate or perchlorate in place of oxygen for anaerobic respiration. Cultures supplied with neither chemical remained viable but showed no measurable growth, distinguishing survival from metabolism. Growth was substantially slower than in control cultures kept at Earth's atmospheric pressure. The researchers also observed dense biofilms in the low-pressure cultures; the sticky secretions appeared to help retain water in the salty solution, with almost no water loss over the experiment. Scott Perl of the Natural History Museum of Los Angeles County and the Blue Marble Space Institute of Science co-led the work. Robinson said the study adds to a growing body of evidence that searches for life on Mars should consider the possibility of extant life, not only fossilized remains from billions of years ago. Perl noted that any Martian microbes would have had billions of years to adapt to conditions we consider hostile. The laboratory did not reproduce every Martian condition: cultures were held at 21 °C (70 °F), far warmer than the actual Martian subsurface, and received researcher-supplied nutrients. The liquid-water pockets the experiment mimics are theorized but not yet confirmed on Mars. Robinson emphasized that the results do not establish life exists on Mars today, but suggest future subsurface missions should look for environments that could support active biology. The work also informs planetary protection by showing how Earth microbes might behave if carried to Mars aboard spacecraft.