Isolation and infection cycle of a polinton-like virus virophage in an abundant marine alga

Isolation and characterization of a selfish genetic element with a virophage lifestyle that co-infects a bloom-forming polar algae along with a partner virus. Virophages are small double stranded DNA (dsDNA) viruses that can only replicate in a host by co-infecting with another virus. Marine algae are commonly associated with virophage-like elements such as Polinton-like viruses (PLVs) that remain largely uncharacterized. Here we isolated a PLV that co-infects the alga Phaeocystis globosa with the Phaeocystis globosa virus-14T (PgV-14T), a close relative of the Phaeocystis globosa virus-virophage genomic sequence. We name this PLV 'Gezel-14T. Gezel is phylogenetically distinct from the Lavidaviridae family where all known virophages belong. Gezel-14T co-infection decreases the fitness of its viral host by reducing burst sizes of PgV-14T, yet insufficiently to spare the cellular host population. Genomic screens show Gezel-14T-like PLVs integrated into Phaeocystis genomes, suggesting that these widespread viruses are capable of integration into cellular host genomes. This system presents an opportunity to better understand the evolution of eukaryotic dsDNA viruses as well as the complex dynamics and implications of viral parasitism.

Automated summary

Isolation and characterization of a virophage-like element, Gezel-14T, that co-infects a polar algae, Phaeocystis globosa, with a partner virus, PgV-14T, is reported. This co-infection reduces the fitness of the viral host by decreasing burst sizes of PgV-14T. Genomic screens reveal the integration of Gezel-14T-like elements into Phaeocystis genomes, suggesting the capability of these widespread viruses to integrate into cellular host genomes.