Genome variation in the hyperthermophilic archaeon .

spp are aerobic, heterotrophic, and hyperthermophilic marine archaea. There are two closely related species, and , which are isolated from geographically distinct locations. Recently, we compared their genome sequences to determine their genomic variation. They possess highly conserved small genomes, reflecting their close relationship. The entire genome similarity may result from their survival strategies in adapting to extreme environmental conditions. Meanwhile, synteny disruptions were observed in some regions including clustered regularly interspaced short palindromic repeats elements. Further, the largest portion of their non-orthologous genes were genes in the two proviral regions of ( spindle-shaped virus 1 and ovoid virus 1) or ORFans considered to be derived from viruses. Our data shows that genomic diversification of spp may be substantially induced by viruses. This suggests that spp may have a large pan-genome that can be extended by viruses, while each of the species shares a highly conserved small genome specializing for extreme environments.