Three simple words follow the water have become the mantra of astrobiologists studying the Red Planet because the presence of water is believed to be a prerequisite for life, either past or present.

But as scientists look for evidence of water on Mars, they are faced with an underlying dilemma: Will they know life when they see it?

"Scientists' approach to finding life is very earth-centric," said Kenneth Nealson, holder of the USC Wrigley Chair in Environmental Sciences. "Based on what we know about life on Earth, we set the limits for where we might look on other planets."

In a paper published in the current edition of the journal Astrobiology, Nealson and Bruce Jakosky of the University of Colorado speculated that a microbe that exists in the coldest temperatures on Earth might provide clues about how a similar organism could survive beneath the Martian polar ice caps.

The microbe in question was discovered by Corien Bakersman, a former postdoctoral student in Nealson's lab, and remains the only one of its kind. It was isolated from a cryopeg a small, salty, liquid lake found under the Siberian permafrost.

The bacteria, named psychrobacter cryopegella, can grow at -10 Celsius and can stay alive and even keep metabolizing at an astonishing -20 Celsius. While it isn't able to replicate itself at that extreme temperature, it maintains the minimal metabolism needed to repair and maintain its cell structures.

"This organism can exist at colder temperatures than any previously discovered," said Nealson, a professor of earth sciences and biological sciences in the USC College of Letters, Arts and Sciences.

"We know it's possible here, so certainly it's possible somewhere else. This bacteria expands the limits
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Contact: Usha Sutliff
sutliff@usc.edu
213-740-0252
University of Southern California
9-Dec-2003