A hardy microbe from Earth might one day transform the barren ground of Mars into arable soil.

By Dr Tony Phillips

When the first humans travel there to explore the Red Planet up close, they will have to grow their food in airtight, heated greenhouses. The Martian atmosphere is far too cold and dry for edible plants to grow in the open air. But if humans ever hope to establish long-term colonies on their planetary neighbour, they will no doubt want to find a way to farm outdoors. Imre Friedmann has an idea of how they might take the first step. 

Friedmann is a microbiologist on the NASA Astrobiology Institute team at the Ames Research Centre. Friedmann was one of the invited speakers at a NASA-sponsored conference, "The Physics and Biology of Making Mars Habitable," held at Ames late last year. His talk focused on an organism that could be used to begin the process of converting the Martian surface into arable soil.

Mars is covered by a layer of ground-up rock and fine dust, known as regolith. To convert regolith into soil, it will be necessary to add organic matter, much as organic farmers on Earth fertilise their soil by adding compost to it. 

On Earth, compost is made up primarily of decayed vegetable matter. Micro-organisms play an important role in breaking down dead plants, recycling their nutrients back into the soil so that living plants can reuse them. But on Mars, says Friedmann, where there is no vegetation to decay, the dead bodies of the micro-organisms themselves will provide the organic matter needed to build up the soil.

The trick is finding the right microbe. 

"Among the organisms that are known today," says Friedmann, "Chroococcidiopsis is most suitable" for the task. 

Chroococcidiopsis is one of the most primitive bacteria known. What makes it such a good candidate is its ability to survive in a wide range of extreme environments that are hostile to most other forms of life. Chroococcidiopsis has been found growing in hot springs, in hypersaline (high-salt) habitats, in a number of hot, arid deserts throughout the world, and in the frigid Ross Desert in Antarctica. 

"Chroococcidiopsis is the constantly appearing organism in nearly all extreme environments," Friedmann points out, "at least extreme dry, extreme cold, and extremely salty environments. This is the one which always comes up."

Moreover, where Chroococcidiopsis survives, it is often the only living thing that does. But it gladly gives up its dominance when conditions enable other, more complex forms of life to thrive.

A photomicrograph of Chroococcidiopsis, enlarged 100 times.

For clues on how to farm Chroococcidiopsis on Mars, Friedmann looks to its growth habits in arid regions on Earth. In desert environments, Chroococcidiopsis grows either inside porous rocks, or just underground, on the lower surfaces of translucent pebbles. 

The pebbles provide an ideal microenvironment for Chroococcidiopsis in two ways. First, they trap moisture underneath them. Experiments have shown that small amounts of moisture can cling to the undersurfaces of rocks for weeks after their above-ground surfaces have dried out. Second, because the pebbles are translucent, they allow just enough light to reach the organisms to sustain growth.

Friedmann envisions large farms where the bacteria are cultured on the underside of strips of glass that are treated to achieve the proper light-transmission characteristics. Mars today, however, is too cold for this technique to work effectively. Before even as hardy a microbe as Chroococcidiopsis could be farmed on Mars, the planet would have to be warmed up considerably, to just below the freezing point.

In many desert environments, Chroococcidiopsis grows on the undersides of transparent rocks, just below the surface.

Friedmann, admits that his ideas about growing Chroococcidiopsis are, at this point, merely a thought experiment. 

"I don't think any of us alive today will see this happen," he muses. When the time does come to make Mars a more habitable place, "the technology will be so different that everything we plan today... will be ridiculously outdated." 

Friedmann fully expects that genetic engineering will eventually develop designer organisms to do the job. Even if Chroococcidiopsis is ultimately used as the basis, it will be a vastly improved version of today's microbe.