The increasing number of genome sequences of archaea and bacteria show their adaptation to different environmental conditions at the genomic level. Aeropyrum spp. are aerobic and hyperthermophilic archaea. Aeropyrum camini was isolated from a deep-sea hydrothermal vent, and Aeropyrum pernix was isolated from a coastal solfataric vent. To investigate the adaptation strategy in each habitat, we compared the genomes of the two species. Shared genome features were a small genome size, a high GC content, and a large portion of orthologous genes (86 to 88%). The genomes also showed high synteny. These shared features may have been derived from the small number of mobile genetic elements and the lack of a RecBCD system, a recombinational enzyme complex. In addition, the specialized physiology (aerobic and hyperthermophilic) of Aeropyrum spp. may also contribute to the entire-genome similarity. Despite having stable genomes, interference of synteny occurred with two proviruses, A. pernix spindle-shaped virus 1 (APSV1) and A. pernix ovoid virus 1 (APOV1), and clustered regularly interspaced short palindromic repeat (CRISPR) elements. Spacer sequences derived from the A. camini CRISPR showed significant matches with protospacers of the two proviruses infecting A. pernix, indicating that A. camini interacted with viruses closely related to APSV1 and APOV1. Furthermore, a significant fraction of the nonorthologous genes (41 to 45%) were proviral genes or ORFans probably originating from viruses. Although the genomes of A. camini and A. pernix were conserved, we observed nonsynteny that was attributed primarily to virus-related elements. Our findings indicated that the genomic diversification of Aeropyrum spp. is substantially caused by viruses.
Between closely related organisms, gene repertoires and genome organizations differ depending on the ecological characteristics of each habitat. For example, whole-genomic comparisons of the cyanobacterial Prochlorococcus spp., with physiological features relevant to the different ecological niches within a stratified oceanic water column, show gross signatures of this niche differentiation (1). The members of the anaerobic hyperthermophilic archaeal genus Pyrococcus adapt to abiotic and biotic environmental conditions through positive gene selection (2). Although genomes of temperate coastal SAR11 isolates are highly conserved in the core genome common to all strains (3) and show synteny (the conservation of DNA sequence and gene order) (4), variations exist among genes for phosphorus metabolism, glycolysis, and C 1 metabolism. This suggests that adaptive specialization in nutrient resource utilization is important for niche partitioning (5).Aeropyrum species are heterotrophic, aerobic, neutrophilic, and hyperthermophilic archaea. The two currently known species, Aeropyrum pernix and Aeropyrum camini, were isolated from geographically distinct locations. The type strain of the type species, A. pernix K1, was isolated from a coastal solfataric vent on Kodakara-Jima Island in southwes...