Bacteria on ice.

Kangaroos bounce around the arid lands of Australia, but they don't make anywhere else their home. This geographic isolation results, in part, from the inability of large animals to disperse easily to other suitable environments around the world.

Bacteria, whose microscopic size allows them to spread by water, air, seeds, and a variety of mobile organisms, shouldn't have that problem, notes James T.

Staley of the University of Washington in Seattle. At least that's what microbiologists have speculated, he says. Anywhere bacteria can survive, they should probably exist, goes the theory.

Staley's research over the last 5 years offers evidence to the contrary, however. His group has collected bacteria from the bottom of sea ice that builds up every winter at the North and South Poles. "Nobody else has really looked in this environment. Most of the organisms are brand-new," says Staley.

Despite almost identical habitats, none of the bacteria so far found under the North Pole ice has been collected at the South Pole, and vice versa.

Understanding this surprising geographic diversity of bacteria should help investigators estimate the true number of bacterial species, of which we know perhaps 1 percent, says Staley.