Friday, October 10, 2008

Single organism ecosystem

Photo credit: Environmental Stress Pathway Project

From harsh conditions in the depths of the earth (in water 2.8 miles underground in a South African gold mine - in total darkness, without oxygen, and at 140 degrees Fahrenheit) scientists have brought forth and gene-sequenced a single-celled bacterium. Desulforudis audaxviator (so named after a passage from a Jules Verne novel).

"... D. audaxviator survives in a habitat where it gets its energy not from the sun but from hydrogen and sulfate produced by the radioactive decay of uranium. Living alone, D. audaxviator must build its organic molecules by itself out of water, inorganic carbon, and nitrogen from ammonia in the surrounding rocks and fluid... D. audaxviator can get its carbon from a number of sources, depending on the local surroundings. It can digest sugars and amino acids, suggesting that one source of carbon might be the dead cells of other microbes in locations .... its genome also contains genes equipping the organism to get carbon from carbon monoxide, carbon dioxide, bicarbonate, formate, and other nonbiological sources. Its nitrogen comes from ammonia released from rocks and dissolved in the fluid at level 104, but D. audaxviator also has a gene for a nitrogenase that could, if necessary, extract nitrogen from its surroundings after first converting it to ammonia – a gene that also appears to be shared with high-temperature archaea... traits as defense against viruses, but one system of self-protection is unique to D. audaxviator 's bacterial phylum, Firmicutes: the ability to form endospores, tough structures that shield DNA and RNA from drying out, and from heat, starvation, and chemical attack..."

This joins a long list of 'extremophile' forms of life which can survive under extraordinarily harsh conditions, including:
  • Pyrolobus fumari, which survives temperatures of 113 degrees Celsius in hydrothermal vents at the bottom of the ocean.
  • Colwellia psychrerythrae, which possibly can survive cold down to negative 196 degrees Celsius
  • Natronomonas pharaonis, which can survive alkaline conditions to a pH of twelve.
  • Genus Picrophilus, which can survive acidic conditions to a pH of zero.
Given the presence of life in areas apparently so inhospitable to it, might not life exist elsewhere in the universe?

Goldmine bug DNA may be key to alien life
The Complete Genome of the Uncultivated Bacterium Desulforudis audaxviator
The most extreme life forms in the universe