Get the gold bug

Dylan Chivian of the Lawrence Berkeley National Laboratory, California, studied the genes found in samples of the fluid to identify the organisms living within it, expecting to find a mix of species. Instead, he found that 99.9% of the DNA belonged to one bacterium, a new species. The remaining DNA was contamination from the mine and the laboratory.

"The fact that the community contains only one species stands one of the basic tenets of microbial ecology on its head," says Carl Pilcher, director of the NASA Astrobiology Institute, who was not involved in Chivian's DNA analysis but whose team made the initial discovery that there were microbes living in this particular fissure two years ago.

A community of a single species is almost unheard of in the microbial world. It means the ecosystem's only species must extract everything it needs from an otherwise dead environment.

"Virtually all other known ecosystems on Earth that don't use sunlight directly do use some product of photosynthesis," says Pilcher.

Deep-sea vent communities, for instance, are too far down to directly use sunlight but they do use oxygen dissolved in seawater, and that oxygen is produced by photosynthesising plankton at the surface.

Chivian's analysis shows that D. audaxviator gets its energy from the radioactive decay of uranium in the surrounding rocks. It has genes to extract carbon from dissolved carbon dioxide and other genes to fix nitrogen, which comes from the surrounding rocks. Both carbon and nitrogen are essential building blocks for life as we know it, and are used in the building blocks of proteins, amino acids. D. audaxviator has genes to produce all the amino acids it needs.

"One question that has arisen when considering the capacity of other planets to support life is whether organisms can exist independently, without access even to the Sun," says Chivian. "The answer is yes and here's the proof. It's philosophically exciting to know that everything necessary for life can be packed into a single genome."