Deinococcus radiodurans is an extremophilic bacterium that can survive high doses of radiation, cold, dehydration, vacuum, and acid. It is one of the most radiation-resistant organisms known and has been listed as the world’s toughest known bacterium in The Guinness Book Of World Records.
But what is the evolutionary origin of this remarkable microbe? And which of these is most closely related to D. radiodurans?
Classification and phylogeny of D. radiodurans
D. radiodurans belongs to the domain Bacteria, the phylum Deinococcota, the class Deinococci, the order Deinococcales, the family Deinococcaceae, and the genus Deinococcus.
The genus Deinococcus contains 11 known species, all of which are radioresistant: D. proteolyticus, D. radiopugnans, D. radiophilus, D. grandis, D. indicus, D. frigens, D. saxicola, D. marmoris, D. deserti, D. geothermalis, and D. murrayi; the latter two are also thermophilic.
The closest relative of D. radiodurans is D. proteolyticus, which shares 97% 16S rRNA sequence similarity and 80% DNA-DNA hybridization with it. Both species have similar cell morphology (spherical tetrads), genome structure (two circular chromosomes and two plasmids), and metabolic features (aerobic heterotrophs that can degrade proteins).
The next closest relatives of D. radiodurans are D. radiopugnans and D. radiophilus, which share 94% 16S rRNA sequence similarity and 60% DNA-DNA hybridization with it. These species differ from D. radiodurans in their cell morphology (spherical pairs or single cells), genome structure (one circular chromosome and one plasmid), and metabolic features (aerobic heterotrophs that cannot degrade proteins).
The other members of the genus Deinococcus are more distantly related to D. radiodurans, sharing less than 90% 16S rRNA sequence similarity and less than 40% DNA-DNA hybridization with it. They also differ from D. radiodurans in various aspects of their cell morphology, genome structure, metabolic features, and ecological niches.
Conclusion
D. radiodurans is a unique bacterium that can withstand extreme conditions that would kill most other living organisms. It belongs to a group of radioresistant bacteria that are classified in the genus Deinococcus.
The most closely related species to D. radiodurans is D. proteolyticus, followed by D. radiopugnans and D. radiophilus.
The other species in the genus Deinococcus are more distantly related to D. radiodurans and have different characteristics and habitats.
