Identification of signature proteins that are distinctive of the Deinococcus-Thermus phylum

The members of the Deinococcus-Thermus phylum, which include many species that are resistant to extreme radiation, as well as several thermophiles, have been recognized solely on the basis of their branching patterns in 16S rRNA and other phylogenetic trees. No biochemical or physiological characteristic is currently known that is unique to this group of species. To identify genes/proteins that are exclusive of this group of species, systematic protein basic local alignment tool (Blastp) searches were carried out on each open reading frame (ORF) in the genome of Deinococcus radiodurans. These studies identified 65 proteins that were only found in all three sequenced Deinococcus-Thermus genomes (viz. D. radiodurans, D. geothermalis and Thermus thermophilus), but not in any other bacteria. In addition, these studies also identified 206 proteins that are exclusively found in the two Deinocococci species, and 399 proteins that are unique to D. radiodurans. The identified proteins, which represent a genetic repertoire distinctive to the Deinococcus-Thermus group, or to Deinococci species, provide novel molecular markers for their identification and characterization. The cellular functions of most of these proteins are not known and their studies should prove useful in identifying novel biochemical and physiological characteristics that are exclusive of these groups of bacteria and also those responsible for the extreme radiation resistance of Deinococci.