A fracture deep underground in a South African gold mine holds a rare biological find--an ecosystem populated by a single species of bacteria. An analysis of the bacterium's complete genetic makeup, published October 10 in Science, reveals that the species has all the tools to survive completely alone.

"This really stands one of the basic tenets of microbial ecology on its head" says Carl Pilcher, director of the NASA Astrobiology Institute at Ames Research Center in Mountain View, Calif. Scientists have thought that any microbial community would contain a variety of species, each specialized to grow on different nutrients. Some microbes would make byproducts that others could use.

Not only does the newly characterized bacterium live alone, but it also appears to live independently of the sun-powered system that helps nourish all other organisms on, or in, the Earth. (Even bacteria that get energy from chemical reactions get some nutrients indirectly from solar energy.) "This is the first pretty solid evidence that there is another source of energy life can use, and that is radioactive energy," says Pilcher, who was not part of the study team. The finding indicates that other rocky planets could support subsurface life, he says. …