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Rock-Eating Microbes

By Sean Henahan, Access Excellence

Washington, DC (8/13/98)- The existence of rock-eating microbes one mile beneath the ocean floor may enhance the search for life on other planets.

Oceanographers participating in the Ocean Drilling Program now report the presence of abundant microbial fossils in basalt rock one mile beneath the Pacific, Atlantic and Indian ocean floors.

Where the basalt was glassy, having quickly been cooled by sea water, the scientists found a series of tracks and trails. "Whenever we looked at those tracks for DNA, we found it," Martin R. Fisk, an associate professor of oceanography at Oregon State University.

The rocks themselves have the basic elements for life including carbon, phosphorous and nitrogen, and require only water to complete the formula. Groundwater seeping through the ocean floor could easily provide that, he notes.

"Under those conditions, microbes could live beneath any rocky planet," Fisk said. "It would be no problem to have life inside of Mars, or within a moon of Jupiter, or even on a comet containing ice crystals that gets warmed up when the comet passes by the sun."

The researchers believe the microbes were originally carried beneath the ocean floor in seawater, seeping into the basalt and settling in fractures created by cooling. Inside of dying, however, the microbes found the necessary ingredients within the basalt to continue living. The DNA was found in the most far-reaching tubes within the fractures, Fisk said, indicating the microbial activity took place on site, beneath the ocean floor.

Martian meteorites that have landed on Earth have revealed a lot about the interior of the red planet. Studies of these meteorites reveal the presence of carbon, phosphorous, small amounts of nitrogen, and minerals that contain water, or evidence of water, "everything you need for life," he said.

While Mars was once considered far too cold to support any form of life, new evidence of life forms surviving in extreme conditions on our own planet, from the steam in geysers to the ice in Antarctica, have changed this attitude. Microbes have been found near temperatures reaching 113 degrees C, and in freezing brines some 15 degrees below zero, leading researchers to believe Mars could support life.

"The surface of Mars may be too cold to find life unless there is a hot spring bubbling up," Fisk said. "But every planet has a temperature gradient; they get hotter as you go down. Within the next few years, we'll probably find life on Mars. But we may have to dig to find it."

Hydrogen Controversy

Meanwhile, related research performed by researchers at the University of Massachusetts at Amherst questions a leading hypothesis on how these extremeophiles survive. While it had been generally accepted that hydrogen gas produced when basalt reacts with water could provide energy to support the growth of microorganisms living below Earth's surface, the researchers report that there is no such hydrogen production under the conditions  found in Earth's subsurface.

The researchers found that hydrogen could only be produced from the basalt when the rock was exposed to acidic conditions, but environments containing basalt are never acidic.

"The idea that hydrogen produced from rocks could support large subsurface microbial ecosystems on Earth and possibly other planets was fascinating and was accepted by most microbiologists. Unfortunately, this concept can not be supported by the available data." says U. Mass. microbiologist Derek Lovley.

Rather a new analyses of chemical and microbiological data suggest that the extreme microorganisms are probably living on organic matter associated with the rock, not hydrogen. This is similar to the way that microorganisms grow in soil on Earth's surface.

The scientists emphasized that even though the microorganisms living deep in the Earth may make a living in a manner similar to that of surface microorganisms, they may have other unique characteristics. For example, Lovley's recent research has demonstrated that microorganisms from the earth's subsurface can be used to remove radioactive metals, as well as hydrocarbons from polluted groundwater.

"This is an important step forward in our continuing efforts to understand the processes that sustain life deep beneath the earth's surface," says Mike Purdy, director of  the National Science Foundation's Life in Extreme Environments (LeXeN) program  "Negative findings like this are as important as positive ones in their importance to our understanding of the processes that determine the limits to life."

The research appears in the August 14, 1998 issue of Science. 


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