Methanogenic lifeforms have survived under simulated Martian conditions. The discovery not only represents a small boost for the chances of life on Mars, but also demonstrates that, if the red planet turns out to be sterile, it would be relatively easy for us to terraform it.
In the quest for life on Mars it is often assumed that if simple forms of life were to evolve there they would only need water and salts to survive. However, Rebecca Mickol, a PhD student at the University of Arkansas, pointed out to the American Society for Microbiology's annual conference that, “The low surface pressure of Mars (7 mbar) is one condition that any extant life at the surface or near subsurface would need to endure.”
Deeper within Mars, pressures increase, but life at depth may face other challenges.
As even at the top of Mount Everest the pressure is 300mb, no life on Earth has got used to facing such conditions. Nevertheless, Mickol wanted to see whether it would be a problem for single-celled organisms to adapt.
She chose four species that turn hydrogen and carbon dioxide into methane (Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum and Methanococcus maripaludis), collectively known as methanogens, and tested their ability to survive in water under pressures as low as 6 mbar. The chamber in which the organisms and their water solution were placed was given a thin atmosphere of 80% hydrogen and 20% carbon dioxide. The species are all members of the Archaea, which are neither bacteria nor eukaryotes.
All four species survived the ordeal, demonstrating that low pressures are not an inherent obstacle to life, even among species that have not had time to acclimatize. The work follows Mickol's previous demonstrations that two species can survive being repeatedly frozen and thawed in a manner likely to be experienced by Martian life.
“These organisms are ideal candidates for life on Mars,” Mickol said. “All methanogen species displayed survival after exposure to low pressure, indicated by methane production in both original and transfer cultures following each experiment.” Since methane is a powerful greenhouse gas, their widespread presence would warm the planet.
When Curiosity detected methane last year the possibility that it might have come from methanogenic species created great excitement, although volcanic sources are also possible. Debate continues as to the possibility that the source may be Curiosity itself.
The downside of the discovery is that organisms that sneak on board robotic missions to Mars may flourish there, whether we want them to or not, emphasizing the need to thoroughly sterilize whatever we send to Mars, until we know if it already has life.
Another presentation in the same session found that many of the microbes collected from the Viking probes prior to sterilization are untroubled by salty environments, such as those on Mars.