The phylum Deinococcus-Thermus consists of a single class (Deinococci) and two orders:
The Deinococcales include two families (Deinococcaceae andTrueperaceae), with three genera, Deinococcus, Deinobacterium and Truepera.Truepera radiovictrix is the earliest diverging member of the order. Within the order, Deinococcus forms a distinct monophyletic cluster with respect to Deinobacterium and Truepera species. The genus includes several species that are resistant to radiation; they have become famous for their ability to eat nuclear waste and other toxic materials, survive in the vacuum of space and survive extremes of heat and cold.
The Thermales include several genera resistant to heat (Marinithermus, Meiothermus, Oceanithermus, Thermus, Vulcanithermus, Rhabdothermus) placed within a single family, Thermaceae. Phylogenetic analyses demonstrate that within theThermales, Meiothermus and Thermus species form a monophyletic cluster, with respect to Marinithermus, Oceanithermus, Vulcanithermus and Rhabdothermus that branch as outgroups within the order. This suggests that Meiothermus and Thermus species are more closely related to one another relative to other genera within the order.Thermus aquaticus was important in the development of the polymerase chain reaction where repeated cycles of heating DNA to near boiling make it advantageous to use a thermo-stable DNA polymerase enzyme.
Though these two groups evolved from a common ancestor, the two mechanisms of resistance appear to be largely independent.
Molecular signatures in the form of conserved signature indels (CSIs) and proteins (CSPs) have been found that are uniquely shared by all members belonging to the Deinococcus-Thermus phylum. These CSIs and CSPs are distinguishing characteristics that delineate the unique phylum from all other bacterial organisms, and their exclusive distribution is parallel with the observed differences in physiology. CSIs and CSPs have also been found that support order and family-level taxonomic rankings within the phylum. Some of the CSIs found to support order level distinctions are thought to play a role in the respective extremophilic characteristics. The CSIs found in DNA-directed RNA polymerase subunit beta and DNA topoisomerase I in Thermales species may be involved in thermophilicity, while those found in Excinuclease ABC, DNA gyrase, and DNA repair protein RadA in Deinococcales species may be associated with radioresistance. Two CSPs that were found uniquely for all members belonging to the Deinococcus genus are well characterized and are thought to play a role in their characteristic radioresistant phenotype. These CSPs include the DNA damage repair protein PprA the single-stranded DNA-binding protein DdrB.
Additionally, some genera within this group, including Deinococcus, Thermus and Meiothermus, also have molecular signatures that demarcate them as individual genera, inclusive of their respective species, providing a means to distinguish them from the rest of the group and all other bacteria. CSIs have also been found specific for Truepera radiovictrix .
Genus Thermus Brock and Freeze 1969 emend. Nobre et al. 1996
Genus Meiothermus Nobre et al. 1996 emend. Albuquerque et al. 2009
Genus Marinithermus Sako et al. 2003
Genus Oceanithermus Miroshnichenko et al. 2003 emend. Mori et al. 2004
Genus Rhabdothermus Steinsbu et al. 2011
Genus Vulcanithermus Miroshnichenko et al. 2003
Currently there are 10 sequenced genomes of strains in this phylum.
Deinococcus radiodurans R1
Thermus thermophilus HB27
Thermus thermophilus HB8
Deinococcus geothermalis DSM 11300
Deinococcus deserti VCD115
Meiothermus ruber DSM 1279
Meiothermus silvanus DSM 9946
Truepera radiovictrix DSM 17093
Oceanithermus profundus DSM 14977
The two Meiothermus species were sequenced under the auspices of the Genomic Encyclopedia of Bacteria and Archaea project (GEBA), which aims at sequencing organisms based on phylogenetic novelty and not on pathogenicity or notoriety. Currently, the genome of Thermus aquaticus Y51MC23 is in the final stages of assembly by the DOE Joint Genome Institute 
^ abGarrity GM, Holt JG. (2001) Phylum BIV. "Deinococcus–Thermus". In: Bergey’s manual of systematic bacteriology, pp. 395-420. Eds D. R. Boone, R. W. Castenholz. Springer-: New York.
^ abGarrity GM, Bell JA, Lilburn TG. (2005) Phylum BIV. The revised road map to the Manual. In: Bergey’s manual of systematic bacteriology, pp. 159-220. Eds Brenner DJ, Krieg NR, Staley JT, Garrity GM. Springer-: New York.
^ abcdefgHo J, Adeolu M, Khadka B, Gupta RS (2016). "Identification of distinctive molecular traits that are characteristic of the phylum "Deinococcus-Thermus" and distinguish its main constituent groups". Syst Appl Microbiol. 39 (7): 453–463. doi:10.1016/j.syapm.2016.07.003. PMID27506333.