Hugo Bisio (@molbiolgv.bsky.social)

A giant virus awakens virophage-like PLVs in the green alga Tetraselmis Giant double-stranded DNA viruses infecting microalgae often interact with polinton-like viruses (PLVs), yet their dynamics within natural hosts remain poorly understood. Here, we report the isolation of a new Tetraselmis striata giant virus (Allomimiviridae) from Mediterranean coastal waters, which we designate Oceanusvirus lionense (TetV-2). From the same sample, we co-isolated a PLV, Tsa-S2b, that replicates concomitantly with TetV-2. Remarkably, TetV-2 infection also reactivates at least two additional PLVs integrated into the host genome. We show that these PLVs exert a virophage-like effect, reducing the fitness of the giant virus. Comparative genomics reveals that these virophagic PLVs are related to the autonomous lytic PLV TsV-N1, sharing structural but not replication-associated genes. This newly described pathosystem provides a unique model to investigate the evolution of PLVs and the parasitic mechanisms underlying virophage-giant virus interactions. ### Competing Interest Statement The authors have declared no competing interest. European FEDER Fund, project 1166-39417 Excellence Initiative of Aix-Marseille University A*MIDEX https://www.biorxiv.org/content/10.1101/2025.10.09.676808v1