Life on other planets - and in your tummy

What does your stomach have in common with a nuclear waste dump? They both harbor related bacterial species that love tough environments. It's the latest discovery to show that organic life can thrive under conditions once thought inhospitable.

Emphasize "thrive." It's no news that bacteria live in our stomachs. However, scientists have thought microbes would have a limited existence in that acidic environment. That's not necessarily so, judging from research reported last week in the Proceedings of the National Academy of Science online early edition.

Stanford University microbiologist Elisabeth Bik and colleagues say their "somewhat surprising" findings indicate "that the human stomach may be home to a distinct microbial ecosystem." Its denizens include a bacterium related to one found in radio-active waste dumps. The researchers add that this largely unknown microbial world "may play important, as-yet-undiscovered roles in human health and disease."

This underscores scientists' new awareness that they have to rethink what they consider the environmental limits on biological systems.

Many lines of research show that, whether it's volcanic hot springs, salt-saturated sea water, frigid glaciers, or some other seemingly hostile environment, life is not deterred. This also has important implications in the search for extraterrestrial life.

Jeffrey Walker, John Spear, and Norman Pace at the University of Colorado at Boulder have been looking into microbes that live in the pore spaces of rocks in Yellowstone's inhospitable geothermal environment.

They explained last April in Nature that, since these spaces provide sheltered habitats on Earth, they should be "an important target in the search for life elsewhere in the Solar System." They showed how readily microbes living in such spaces in Yellowstone turn into fossils.

Meanwhile, Mark Williams, a fellow at the university's Institute of Arctic and Alpine Research, and his colleagues had found signs of life in another supposedly barren world - high-altitude rock glaciers. These are masses of rock debris laced with ice. They creep along high above the timber line on mountains.

The research team found microbial "signatures" - not microbes themselves. These "signatures" are dissolved organic matter and nitrates. They are similar to signs of bacterial life found in Antarctica. Once again, scientists had found life where they did not expect it.

Deep salt-saturated basins in the Mediterranean Sea that are devoid of oxygen also would seem an unlikely habitat. Yet Paul van der Wielen at the University of Groningen in The Netherlands and his colleagues have found microbes thriving there.

Reporting their work a year ago in the journal Science they concluded: "Our results indicate that microbial metabolism can proceed at significant levels in some of the most extreme terrestrial hypersaline environments and further support the possibility of extraterrestrial life."

Scientists think some of Earth's tough environments are analogues to environments on other worlds. Dry valleys in Antarctica mimic environments on Mars. So, too, do parts of the bone-dry Atacama Desert in Chile, where microbes live.

It would be too much of a stretch to look for an extraterrestrial analogue in the human stomach. However, the work of Dr. Bik and her colleagues shows that it, too, is a world of bacterial life we have scarcely begun to explore.