Endogenous virophages are active and mitigate giant virus infection in the marine protist Cafeteria burkhardae

• 成果类型: Article
• 署名作者: Koslova, Anna; Hackl, Thomas; Bade, Felix; Kasikovic, Alexander Sanchez; Barenhoff, Karina; Schimm, Fiona; Mersdorf, Ulrike; Fischer, Matthias G.
• 署名单位: Max Planck Society; University of Groningen
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-10054
• DOI: 10.1073/pnas.2314606121
• 发表日期: 2024-03-05
• 关键词: dna viruses; genome; transposons; parasite; ELEMENTS

摘要

Endogenous viral elements (EVEs) are common genetic passengers in various protists. Some EVEs represent viral fossils, whereas others are still active. The marine heterotrophic flagellate Cafeteria burkhardae contains several EVE types related to the virophage mavirus, a small DNA virus that parasitizes the lytic giant virus CroV. We hypothesized that endogenous virophages may act as an antiviral defense system in protists, but no protective effect of virophages in wild host populations has been shown so far. Here, we tested the activity of virophage EVEs and studied their impact on giant virus replication. We found that endogenous mavirus-like elements (EMALEs) from globally distributed Cafeteria populations produced infectious virus particles specifically in response to CroV infection. However, reactivation was stochastic, often inefficient, and poorly reproducible. Interestingly, only one of eight EMALE types responded to CroV infection, implying that other EMALEs may be linked to different giant viruses. We isolated and cloned several reactivated virophages and characterized their particles, genomes, and infection dynamics. All tested virophages inhibited the production of CroV during coinfection, thereby preventing lysis of the host cultures in a dose- dependent manner. Comparative genomics of different C. burkhardae strains revealed that inducible EMALEs are common and are not linked to specific geographic locations. We demonstrate that naturally occurring virophage EVEs reactivate upon giant virus infection, thus providing a striking example that eukaryotic EVEs can become active under specific conditions. Moreover, our results support the hypothesis that virophages can act as an adaptive antiviral defense system in protists.