Since the first Mariner probes reached the Red Planet in the 1960s, it’s become clear just how very alien Mars is and how hard it is to find parallel examples of possible Martian life on Earth. However, it’s not impossible. Rebecca Mickol, a doctoral student in space and planetary sciences at the University of Arkansas, has discovered that two species of methane-producing bacteria can live in the harsh conditions on Mars, and may aid in the search for life there.
The two bacteria in question are called Methanothermobacter wolfeii and Methanobacterium formicicum. These are examples of methanogens, which are among the most ancient forms of life on Earth. The name of the genus may sound exotic, but they're so common that species are found in cow guts, termites, and in any bog where vegetation is rotting and bubbling up swamp gas. That’s because methanogens are an anaerobic bacteria that don’t breathe oxygen. In fact, oxygen is lethal to them. Instead, they ingest hydrogen and carbon dioxide and give off methane gas. In other words, they’re the reason cows fart.
They’re also good candidates for models for Martian life. For one thing, they don’t need ordinary organic nutrients, and they don’t need light because they aren’t photosynthetic. Many species are also extremophiles that can live in conditions that would kill other organisms. They can exist at the temperature of boiling water, and are found under the Greenland ice cap and in deep basaltic rock formations.
With this in mind, Mickol chose her specimens because M. formicicum is a thermophile that thrives in temperatures of 37° C (98.6° F), and M. wolfeii prefers 55° C (131° F). She subjected them to the extreme variations in temperature during the freeze-thaw cycle of a Martian day. She says that though their growth was inhibited, both survived and once they warmed up, they ate and grew again, showing that they could live and adapt on Mars.
"The surface temperature on Mars varies widely, often ranging between minus 90° C (-130° F) and 27° C (80.6° F) over one Martian day,” says Mickol. “If any life were to exist on Mars right now, it would at least have to survive that temperature range. The survival of these two methanogen species exposed to long-term freeze/thaw cycles suggests methanogens could potentially inhabit the subsurface of Mars."
While the discovery of Earth bacteria that could survive on Mars gives insight into what sort of life may exist there, there are still a lot of questions to be answered, such as identifying places on Mars where such bacteria could, or once could, live. Also, the recent findings of the Curiosity lander that there is no measurable methane in the Martian atmosphere indicates that such bacteria, if it ever was on Mars, is now a thing of the past.
Mickol presented her work at the 2014 General Meeting of the American Society for Microbiology, held this week in Boston.
Source: University of Arkansas