Thermoplasma acidophilum belongs to a group of organisms, the archaea, which are often found in extreme environments (high temperatures, high salt concentrations or extreme acidity). In 1970, Thermoplasma was found isolated from self-heated coal refuse piles.
Unusual properties of this organism include the lack of a cell wall, a growth temperature of up to 63°C and being able to adapt to an extremely acidic ecological niche with a range of pH 0.5-4. In comparison: pH 0.5 corresponds to 20% hydrochloric acid. Additionally, some of the essential cellular systems such as components of protein synthesis, protein folding and protein degradation machines exhibit strong similarity to respective systems of higher organisms. Since the archaeal molecules have a simpler composition, they represent a valuable model system for investigating the more complex systems (of higher organisms).
On page 508 of the current issue of Nature, Ruepp and colleagues describe the complete genome sequence of Thermoplasma. Therefore, a new sequencing strategy was established enabling scientists to decode the genome of organisms without extensive infrastructure and manpower. The genes of Thermoplasma were analysed in a collaboration between a German and an American group of scientists.
The genes of Thermoplasma exhibit an unusual strong resemblance to genes of another, distantly related inhabitant of acidic environments, Sulfolobus solfataricus. The related genes are not involved in vital processes in the cell but predominantly in the ability to adapt to the environment.
Most organisms are killed by extreme acidity (pH1) and thus serve as nutrients for scavengers such as Thermoplasma. As a result of this adaptation to the availability of decomposing organisms, Thermoplasma requires extracts of meat or yeast when it is grown in culture.
The genes of the metabolic enzymes that allow the degradation and uptake of nutrients from dead organisms were only identified by a couple of organisms. As a result of the surprising similarity between Thermoplasma and Sulfolobus genes, scientists have suggested that there are two different classes of genes: One is primarily composed of 'housekeeping' genes carrying out/performing the vital metabolism of the cells. The other mostly contains 'life-style' genes, which are tailored to suit a specific environment and are shared between the organisms within one ecological niche.
Complete deciphering of the Thermoplasma acidophilum genome is a prerequisite for two further highly interesting projects: Following the genome analysis, the proteins in Thermoplasma can now be examined. Scientists want to investigate which proteins are synthesized, how many and at what stage. By means of electron tomography analysis with intact but (deeply) frozen Thermoplasma cells, the localization of important protein complexes will be visualized. This should help scientists to obtain a deeper understanding of their cooperation in living cells.
Figure and video: Threedimensional electrontomographic representation of a Thermoplasma cell. Protein complexes that are involved in protein folding or protein degradation are shown (not true to scale) in colour.
Journal
Nature