PH1: an Archaeovirus of Haloarcula hispanica Related to SH1 and HHIV-2

Halovirus PH1 infects Haloarcula hispanica and was isolated from an Australian salt lake. The burst size in single-step growth conditions was 50'100 PFU/cell, but cell density did not decrease until well after the rise (4'6 hr p.i.), indicating that the viruscould exit without cell lysis. Virions were round, 51 nm in diameter, displayed a layered capsid structure, and were sensitive tochloroform and lowered salt concentration. The genome is linear dsDNA, 28,064 bp in length, with 337 bp terminal repeats andterminal proteins, and could transfect haloarchaeal species belonging to five different genera. The genome is predicted to carry49 ORFs, including those for structural proteins, several of which were identified by mass spectroscopy. The close similarity ofPH1 to SH1 (74% nucleotide identity) allowed a detailed description and analysis of the differences (divergent regions) between thetwo genomes, including the detection of repeat-mediated deletions. The relationship of SH1-like and pleolipoviruses to previouslydescribed genomic loci of virus and plasmid-related elements (ViPREs) of haloarchaea revealed an extensive level of recombinationbetween the known haloviruses. PH1 is a member of the same virus group as SH1 and HHIV-2, and we propose the namehalosphaerovirus to accommodate these viruses.