Methanogenic Archaea
Résumé
The hyperthermophilic viruses represent an integral but unique part of the virosphere, with many members displaying exotic morphologies resembling bottles, droplets, lemons, and so on. Spindle-shaped viruses are widespread in archaea-dominated terrestrial and marine environments. The isolated and characterized hyperthermophilic archaea viruses with spindle-shaped morphology have been assigned to two families Fuselloviridae and Bicaudaviridae . Along with the extraordinary diversity of morphotypes, another outstanding feature of hyperthermophilic archaeal viruses is the uniqueness of their genome content, with a very low proportion of genes with recognizable homologues in public databases. The unusual features of hyperthermophilic archaeal viruses extend to the content of their genomes with the vast majority of genes without homologues in viral and cellular genomes. The specific morphological and genomic features of hyperthermophilic archaeal DNA viruses, without counterparts or even strong phylogenetic relationships with other viruses, raises important questions regarding their origins.