Living side by side with a virus: characterization of two novel plasmids from Thermococcus prieurii, a host for the spindle-shaped virus TPV1.

Microbial cells often serve as an evolutionary battlefield for different types of mobile genetic elements, such as viruses and plasmids. Here, we describe the isolation and characterization of two new archaeal plasmids which share the host with the spindle-shaped Thermococcus prieurii virus 1 (TPV1). The two plasmids, pTP1 and pTP2, were isolated from the hyperthermophilic archaeon Thermococcus prieurii (phylum Euryarchaeota), a resident of a deep-sea hydrothermal vent located at the East Pacific Rise at 2,700-m depth (7°25'24 S, 107°47'66 W). pTP1 (3.1 kb) and pTP2 (2.0 kb) are among the smallest known plasmids of hyperthermophilic archaea, and both are predicted to replicate via the rolling-circle mechanism. The two plasmids and the virus TPV1 do not have a single gene in common and stably propagate in infected cells without any apparent antagonistic effect on each other. The compatibility of the three genetic elements and the high copy number of pTP1 and pTP2 plasmids (50 copies/cell) might be useful for developing new genetic tools for studying hyperthermophilic euryarchaea and their viruses.