1Titech-ELSI, 2Institut Pasteur (Paris, France)
Viruses are found from members of all three domains of life, archaea, bacteria and eukarya. Viruses of the archaea are the least studied biological group, although it is well known that they are clearly distinct from viruses of bacteria or eukarya. Here we describe the newly isolated hyperthermophilic archaeal virus, Pyrobaculum filamentous virus 1 (PFV1). Both the virus and its host Pyrobaculum sp., which grows at 90 degrees, were isolated from a terrestrial hot spring in Italy. The virion is flexible filamentous shaped. Detergent treatment shows that the nucleoprotein core is surround with lipidous envelope. The cultured PFV1 exists as a mixed population of genetic variants. Sequencing of its double-stranded DNA genome yielded two contigs displaying large insertions/deletion with respect to each other. Morphologically PFV1 is most similar to Thermoproteus tenax virus 1 (TTV1), the sole member of the viral genus Alphalipothrixvirus, within the family Lipothrixviridae. PFV1 and TTV1 shares 12 genes, including the capsid proteins. However no sequence similarity is seen with other members of the Lipothrixviridae family. Both morphological and genetic features, along with their host range, indicate that PFV1 and TTV1 may not have shared their evolutionary relationship with other viruses of the Lipothrixviridae. These results suggest an establishment of a novel taxonomical family for TTV1 and PFV1.