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June 1, 2009

Extremophile Hunter

The search is on for extremophiles that may provide insights about life elsewhere in the cosmos

Astrobiologist Richard Hoover really goes to extremes to find living things that thrive where life would seem to be impossible--from the glaciers of the Alaskan Arctic to the ice sheets of Antarctica.

"I have personally been to many of the most hostile and extreme environments on Earth," said Hoover.

These so-called "extremophiles" are bacteria that have adapted to living in harsh conditions. They were unknown to scientists until just a few years ago. But then researchers started finding these hearty microbes flourishing in unlikely places--like inside the geysers of Yellowstone National Park, and within deep-sea hydrothermal vents, called "black smokers."

"Aside from the deep interior core of the Earth, microorganisms seem to be able to thrive anywhere else," said Hoover. "That includes the atmosphere, that includes the deep crustal rocks."

A scientist at NASA's Marshall Space Flight Center in Huntsville, Ala., Hoover has gone literally to the ends of the Earth in search of extremophiles--including an expedition to Antarctica's remote Lake Untersee in 2008 that was coordinated through the National Science Foundation.

Back at the lab

Once Hoover harvests the extremophiles, the race is on back at his laboratory in Alabama to grow them. First order of business--find out what they like to eat.

"There are a whole array of bacteria that live entirely on chemicals. They don't utilize light, they don't utilize ordinary food," he said. "There is an exquisite suite of life that is phenomenally diverse and tremendously interesting, with profound ability for human applications in biotechnology."

Russian microbiologist Elena Pikuta collaborates with Hoover to isolate and classify the extremophiles. She recently discovered that one microbe that he gathered from beneath the ice of Lake Untersee eats hydrogen and is a "chemolithotroph," which literally means "rock eater." It is related to a rare type of bacteria she has seen before.

"They were discovered very recently, I would say (in the) last ten years," said Pikuta. "They were discovered in (a) cold polar region of swamps in Russia. I think, right now, known (are) just four or five species. So this is a potential new species from Antarctica."

Clues to other life forms

So what is NASA's interest in these extremophiles? Hoover says they may provide telling clues as to what life elsewhere in our solar system might look like. His field of research, called astrobiology, looks at the possibility that life forms elsewhere might be a lot like the extremophiles that live in similar harsh conditions here on Earth.

"I think it is quite possible that when we go by spacecraft to collect samples from the icy moons of Jupiter or to collect samples from the polar ice caps of Mars, we may very well find microorganisms," he said.

He thinks it is even possible that over the course of billions of years, life has spread around the solar system--a sort of cosmic cross pollination. Microbes could live in the ice deep within comets, frozen there for eons until a collision with another planet or moon delivered them to a new home.

"It may be that when we ultimately get a chance to bring back samples of ice from the polar caps of Mars, we might find biology that looks just like Earth life and it might be that it originated on Earth and was carried to Mars," said Hoover. "Of course, if it can happen that way, it could have happened the other way. So we may never know the ultimate answer to how did life originate."

Older than the Earth

To test that theory, he cracks open so-called carbonaceous meteorites, which are the remains of cometary debris or water-bearing asteroids that have hit the Earth. Being careful to avoid contamination, he examines their insides with an electron microscope.

"They are older than the planet Earth, which is accepted at being 4.5 billion years old," said Hoover. "So I like to say these carbonaceous meteorites are actually older than dirt!"

Some of the structures he has imaged from these meteorites are intriguing, bearing striking similarities to bacteria here on Earth. Could these be the fossilized remains of extraterrestial life?

"I am convinced that what I am finding in the carbonaceous meteorites are in many cases biological in nature, and I think they are indigenous and not terrestrial contaminants," said Hoover.

It is a highly controversial interpretation.

"We have for a long time thought that all life, as we know it, originated on Earth. And there isn't any life anywhere else," he said. "That's an idea, it's a hypothesis, it's a totally unproven hypothesis."

Hoover hopes his work will help get at the truth, whatever that may be. And as interplanetary probes become more sophisticated, scientists may eventually turn up a biological sample for examination. Then we'll know if life out there looks anything like it does here.