Researchers Find Size Affects Growth Of Microorganisms In Mars-Like Environment

Technical title: Factors Affecting Growth of Methanogens on a Mars Soil Simulant

FAYETTEVILLE, Ark. - When growing microorganisms under some Mars-like conditions, size does matter - at least if you’re talking about the sample size and surface area involved, according to two University of Arkansas researchers.

Tim Kral, professor of biological sciences, and graduate student Curtis Bekkum will present their findings on the morning of Monday, May 22, at the American Society for Microbiology meeting in Los Angeles.

Last year, Kral became the first scientist to grow microbes under some of the conditions found on Mars. Now he is refining his studies to determine factors that affect the growth of the microbes.

"This is a hodgepodge of things that come together and tell a story," Kral said. "You have to put the parts in place before you can see the whole picture. We are currently teasing out the parts so we can build the picture."

Mars appears unfriendly towards most life forms. The planet currently contains no detectable organic matter and has extremely cold surface temperatures. So for his experiment, Kral sought microorganisms that survive in extreme conditions and thrive on inorganic matter.

He found the ideal microbes in methanogens, anaerobic microorganisms considered to be some of the most primitive life forms on earth. Methanogens can be found deep in the ocean, in the earth’s crust or even in a cow’s stomach, all of which are environments that might be considered harsh like Mars’ surface.

To grow methanogens under some of the conditions found on Mars, Kral and Bekkum used ash from Hawaiian volcanoes - known to share chemical characteristics with Mars soil. They also used carbon dioxide, hydrogen and water while growing the microbes. The methanogens grew successfully in the Mars soil simulant, obtaining all the macro and trace minerals they needed to survive.

Kral and Bekkum studied the effects of surface area on growth by growing methanogens in 2 cm2 test tubes and in small bottles the width of a prescription container, about 20 cm2 . They found that for one species, Methanosarcina barkeri, grew best on limited water with the smaller surface area.

The scientists also inoculated the test tubes with different amounts of cells and tested their growth at different water dilutions. M. barkeri grew successfully at both high and low concentrations with limited water and saturated water. The Methanobacterium species both grew more successfully at higher concentrations but not at the same water levels if the concentration was reduced by half.

Kral also wanted to ensure that the methanogen growth was not affected by contaminants in the buffer used to wash the cells before inoculation. To examine this question, he and Bekkum changed the buffer to argon-saturated distilled water, both with and without sodium sulfide to scavenge residual oxygen. The Methanobacterium species grew under these conditions, and M. barkeri grew with the sodium sulfide present.

"It is further evidence that the methanogens are growing on the Mars soil simulant," Kral said.

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EDITOR’S NOTE: Dr. Kral will be at the Westin Bonaventure Hotel May 20-25. The number is (213) 624-1000