updated 1/28/2005 2:44:32 PM ET 2005-01-28T19:44:32

Researchers in Colorado say they have found what fuels microbial dwellers of hot springs in Yellowstone National Park — and it isn't what the rotten-egg smell of the heated pools might suggest.

The team from the University of Colorado at Boulder said the main energy source for microbes is hydrogen — not sulfur.

"You can smell sulfide in the air at Yellowstone, and the accepted idea was that sulfur was the energy source for life in the hot springs," said John Spear, lead author of the report published in the online edition of Proceedings of the National Academy of Sciences.

According to the study, sulfide "seems to play a minor role."

The researchers say the findings could also aid in the understanding of life in other extreme environments, perhaps Mars.

The study, spanning years, was aimed at determining the main source of metabolic energy that drives microbial communities in hot springs over 158 degrees Fahrenheit.  Photosynthesis isn't known to occur at temperatures higher than that, they said.

The researchers studied microbial ecosystems, and collected from hot springs about as much material as a pencil eraser, as well as sediment.

They reached their conclusion by using such methods as genetic analysis of microbes in the communities, observations of hydrogen levels in hot springs and models based on field data.

Norman Pace, a professor who led the research team, said finding hydrogen as the main energy source was a surprise.

"This project is also interesting in the context of microbiology, because it's one of the few times we've been able to study microbes to get information on an entire ecosystem," he said.

Spear said the work also poses other questions. Hydrogen, he said, is the most abundant element in the universe.

"If it works this way on Earth, it's likely to happen elsewhere," he said.  "When you look up at the stars, there is a lot of hydrogen in the universe."

Copyright 2005 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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