Temperate membrane-containing halophilic archaeal virus SNJ1 has a circular dsDNA genome identical to that of plasmid pHH205

A temperate haloarchaeal virus, SNJ1, was induced from the lysogenic host, Natrinema sp. J7-1, with mitomycin C, and the virus produced plaques on lawns of Natrinema sp. J7-2. Optimization of the induction conditions allowed us to increase the titer from ∼104 PFU/ml to ∼1011 PFU/ml. Single-step growth curves exhibited a burst size of ∼100 PFU/cell. The genome of SNJ1 was observed to be a circular, double-stranded DNA (dsDNA) molecule (16,341 bp). Surprisingly, the sequence of SNJ1 was identical to that of a previously described plasmid, pHH205, indicating that this plasmid is the provirus of SNJ1. Several structural protein-encoding genes were identified in the viral genome. In addition, the comparison of putative packaging ATPase sequences from bacterial, archaeal and eukaryotic viruses, as well as the presence of lipid constituents from the host phospholipid pool, strongly suggest that SNJ1 belongs to the PRD1-type lineage of dsDNA viruses, which have an internal membrane.