Microbes in a cave, eating rock

Life abounds on Earth, where it lives in every possible ecological niche, including deep in the crust. This comes from biology’s reproductive drive plus natural selection’s creativity in matching organisms’ needs with what nature provides.

ROCK ENERGY. A phylogenetic tree showing in bold face the microbes, including Pseudomonas, that grew when incubated in a mineral medium with olivine as the sole source of energy. (Image is Figure 2 from the paper.)

But what about Mars, where the environment is markedly harsher than almost any on Earth? A new paper in Astrobiology by a group of scientists led by Radu Popa (Portland State University) describes a common Earth microorganism that’s thriving under conditions approaching those on Mars. The microbe is a bacterium (Pseudomonas sp. HerB) that lives on rock and ice in a lava tube on Newberry volcano in the Oregon Cascades.

In a laboratory at room temperature and normal oxygen levels, the scientists found that the microbes consumes organic material (sugars). But when the researchers removed the organic material, reduced temperatures to near-freezing, and lowered the oxygen levels, the microbes began to use the iron from olivine — a silicate mineral widely found in volcanic rocks on Earth and Mars — as its energy source.

“This reaction involving a common igneous mineral hasn’t been documented before,” says Martin Fisk (Oregon State University), an author on the study. “In volcanic rocks directly exposed to air and at warmer temperatures, the oxygen in the atmosphere oxidizes the iron before the microbes can use it. But in the lava tube, where the bacteria are covered in ice and sheltered from the atmosphere, they out-compete the oxygen for the iron.”

Conditions in the Oregon lava tube are not as harsh as on Mars, Fisk acknowledges. “On Mars, temperatures rarely rise above the freezing point of water, oxygen levels are lower, and at the surface, liquid water is not present. But water is hypothesized to be present in the warmer subsurface of Mars.”

“The metabolic capabilities of this bacterium would allow it to live in near-surface, icy, volcanic environments of Mars in the present or recent geological past,” say the researchers. “This type of physiology is a prime candidate in the search for life on Mars.”


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