Archaea Genomes - THERMOPLASMA ACIDOPHILUM

Thermoplasma acidophilum is a thermoacidophilic archaeon that thrives at 59 degrees C and pH 2, which was isolated from self-heating coal refuse piles and solfatara fields. It is among the most acidophilic organisms known. Species of the genus Thermoplasma lack rigid cell wall, but are only delimited by a plasma membrane.

Microbial physiologists and structural biologists have long been fascinated by the ability of this microorganism to grow at high temperatures and low pH without the structural protection of a conventional cell wall. T. acidophilum is also interesting from an evolutionary perspective. Its cellular morphology seems primitive, and it contains complexes involved in protein folding, degradation and turnover that look like simple versions of related structures in eukaryotic cells. Evolutionary biologists have speculated that T. acidophilum is an ancestor of the eukaryotic cell. Genome sequencing made genome comparison possible and shown that this hypothesis is not true and T. acidophilum genes are closer to the bacteria genes than to to eukaryotic ones.

Evidence indicates that there has been much lateral gene transfer between Thermoplasma and Sulfolobus solfataricus, a phylogenetically distant crenarchaeon inhabiting the same environment. Sulfolobus-like genes in the T. acidophilum genome are clustered into several discrete regions, which seems to suggest that only a few gene-transfer events occurred, each involving movements of large chunks of genetic sequence.

T. acidophilum has 1,564,905 base pairs and is one of the smallest microbial genomes ever sequenced. The genome is a single circular chromosome and was sequenced using a new strategy called "shotgun primer walking". This is a fusion of the shotgun sequencing and the primer walking techniques. This new method is a significant improvement over current sequencing strategies as it is faster and cheaper.

References:

http://www.nature.com/genomics/papers/thermoplasma.html
http://www.biochem.mpg.de/baumeister/genome/