By Laura Grant
An organism that was discovered in a South African gold mine, nearly 3km beneath the Earth's surface, has scientists "buzzing with excitement" because it offers fascinating evidence that life could exist on other planets, say reports.
A community of the organisms was found by researchers in water extracted from a rock fissure in the Mponeng gold mine on the Witwatersrand near Johannesburg.
The rod-shaped bacterium, named Desulforudis audaxviator, exists in total darkness, with no oxygen and in 60°C heat. But, most importantly, it is the first known species to live in isolation in its own ecosystem, say researchers in a report by the Lawrence Berkley National Laboratory in California, one of a number of institutions involved in the research.
"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 Dylan Chivian, the bioinformatics lead scientist at the Joint BioEnergy Institute in Berkeley, California, who studied the gene samples found in the fissure water.
"The answer is yes, and here's the proof. It's sort of philosophically exciting to know that everything necessary for life can be packed into a single genome."
This could be the kind of organism that could survive below the surface of Mars, say scientists. The bacterium gets its energy from hydrogen and sulphate produced by the radioactive decay of uranium, say the researchers. And because it lives alone, they believe that it builds its organic molecules by itself out of water, inorganic carbon, and nitrogen from ammonia in the surrounding rocks and fluid.
A team of scientists reportedly made the discovery that there were microbes in the Mponeng fissure two years ago. "We knew from previous work in these mines, using molecular biology techniques, that there seemed to be very simple communities living down there," says Fred Brockman of the biology department of Pacific Northwest National Laboratory, where the DNA was extracted from the filtered cells.
"We expected we'd have a good chance of assembling one entire genome of the most dominant species, or perhaps 70 to 80 percent of several species."
But, to the researchers' surprise, only one organism was present. Even before the analysis was complete it was evident the lone species's genome was remarkable, the researchers say.
It contained everything needed for the organism to survive and reproduce, including the ability to incorporate the elements necessary for life from inorganic sources, move freely, and protect itself from viruses, harsh conditions, and nutrient-poor periods by becoming a spore.
About the only thing D audaxviator can't do is live in oxygen, which suggests it hasn't been exposed to pure oxygen for a very long time - perhaps millions of years - the researchers say. The water the bacterium lives in, they believe, has not seen the light of day for more than 3 million years, which could be a clue to how old the species is.
D audaxviator's name comes from Jules Verne's Journey to the Centre of the Earth, in which a message in Latin deciphered by Professor Lidenbrock, Verne's protagonist, reads in part, "descende, Audax viator, et terrestre centrum attinges". It means "descend, Bold traveller, and attain the centre of the Earth".