A rolling circle-replicating plasmid as an Inovirus phage satellite

Bacterial viruses (phages) are potent agents of lateral gene transfer and thus are important drivers of evolution. A group of mobile genetic elements (MGEs), referred to as phage satellites, exploit phages to disseminate their own genetic material. Here we isolated a novel member of the genus Inovirus, Shewanella phage Dolos, along with an autonomous rolling circle-replicating plasmid, pDolos. Dolos causes a chronic infection in its host Shewanella oneidensis by phage production with only minor effects on the host cell proliferation. When present, plasmid pDolos hijacks Dolos functions to be predominantly packaged into phage virions and released into the environment. pDolos can disseminate further genetic material encoding, e.g., resistances, fluorophores, and metabolically active proteins, to host cells sensitive to Dolos infection. Given the rather simple requirements of a plasmid for takeover of an inovirus, the wide distribution of phages of this group and the broad spectrum of rolling circle-replicating plasmids, we speculate that similar phage-satellite systems are common among bacteria.