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"SLiME" at Hanford hints at potential for microbes on Mars

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October 24, 1995 Share This!

RICHLAND, Wash. — Two researchers from the Pacific Northwest Laboratory have discovered a microbial ecosystem that is not dependent on photosynthesis -- as most known life forms are in one way or another. Instead, these microbes appear to thrive on chemical energy in basalt, a rock common to Earth and Mars, but basalt that contains little of the organic carbon that usually feeds microorganisms. Although focused on microbial populations deep within the Earth, the research may indicate a potential for life on Mars.

An article on the subsurface microbes research appeared in the Oct. 20 edition of Science, a prestigious peer-reviewed scientific journal.

The microbes were found in groundwater samples taken more than 1,000 meters (3,300 feet) below the surface at the Department of Energy's Hanford site which is situated on the Columbia Basin basalt flows in southeastern Washington state. But researchers say these types of microbes may be widespread.

Called a subsurface lithoautotrophic microbial ecosystem, or SLiME, this community of microbes exists on a diet of mostly hydrogen. Hydrogen- eating bacteria have been identified before, but this SLiME appears to get its hydrogen in an unusual way. Other microbes depend on organic carbon or hydrogen from decaying plant matter that was originally generated from photosyntheses, but the SLiME consume hydrogen given off by a reaction between basalt and groundwater.

"We have several lines of circumstantial evidence that lead us to believe this is the source," said Todd Stevens, PNL microbiologist. Stevens and PNL geochemist Jim McKinley mixed samples of crushed basalt and groundwater, which resulted in hydrogen production. They also detected elevated hydrogen concentrations in basalt groundwaters. The basalt-water- microbial relationship was confirmed in the laboratory when microbes were able to grow in a basalt-water mixture. Finally, geochemical measurements of Columbia Basin groundwaters show traces of just this sort of metabolism occurring in regional aquifers.

As part of DOE's Subsurface Science Program, PNL is interested in studying microorganisms for their potential in transforming or immobilizing hazardous and radioactive waste plumes. There are plans to test the SLiME's effectiveness on different contaminants, but in the meantime, this research may shed light on some less urgent questions.

If the SLiME derives energy from iron-rich minerals in basalt, it could explain how organisms survived on Earth before the evolution of photosynthesis. Scientists say the first life appeared on earth about 4 billion years ago, but photosynthesis began only 2.8 billion years ago.

The basalt connection, in theory, also indicates that microbes could exist in the Martian subsurface. Until recently, experts believed that all water under the surface of Mars was frozen, but conventional wisdom is moving toward the idea that there is liquid water within the Red Planet. If that is true, then the subsurface conditions on Mars are similar to the basalt and water subsurface environments of the Columbia Basin area. This does not mean there is life on Mars, but if SLiME can exist here, then, in theory, it could exist on Mars too.

While NASA or other research organizations could choose to use the PNL findings as part of further research on Martian life, McKinley and Stevens are pursuing more down-to-earth questions.

"Next, we want to find out exactly how the hydrogen is generated and whether the SLiME itself promotes the process, perhaps by eroding the basalt surface," said McKinley.

Details of the SLiME research can be found in the Oct. 20 edition of Science, a journal established by Thomas Edison in 1880. Science reviews and publishes many of the top research papers in the biological and physical sciences and has the highest paid circulation of any scientific journal in the world.

Tags: Energy, Environment, Subsurface Science

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