Molecular Determinants of Virophages activity: A Multi-Level Review
DOI:
https://doi.org/10.63939/w1e2ae66Keywords:
Virophages, giant viruses, virophage lineage, mavirus, Co-entry (hitchhiking), provirophagesAbstract
Virophages are distinctive parasitic viruses that replicate solely within the viral factories of co-infecting giant viruses (GVs), exerting considerable molecular, ecological, and evolutionary effects on host–virus systems. This study offers a comprehensive synthesis of virophage molecular biology, emphasizing structural factors influencing ligand-receptor recognition, genome organization, transcriptional and translational reliance, host and viral tropism, and mechanisms that disrupt giant-virus replication. Structural analyses demonstrate that virophage capsids possess double-jelly-roll major capsid proteins and specialized surface protrusions, including trimeric fiber-head-like receptor-binding folds, which facilitate attachment to glycosylated GV fibrils and enable hitchhiking-based co-entry into protist hosts.
Virophage genomes, usually 17–30 kb dsDNA, contain compact replication modules, packaging ATPases, primase/helicase-like proteins, integrases (in certain lineages like mavirus), and regulatory elements that have evolved to work with the transcriptional machinery of their helper GVs. Once inside the GV viral factory, virophage gene expression follows a pattern of early, middle, and late stages that are mostly controlled by giant-virus polymerases and host ribosomes. RNA metabolism is limited. Capsid–fibril compatibility, promoter recognition specificity, replication-module matching, and viral defense systems like MIMIVIRE, which limit some virophage lineages (like Zamilon), all play a role in host and GV tropism. Integrated provirophage forms, particularly mavirus, exhibit alternative replication strategies that include host-genome integration and giant-virus–induced reactivation, thereby offering sustained antiviral defense at the
population level. Virophage infection alters giant-virus transcription, hinders virion assembly, and diminishes GV burst sizes, resulting in significant ecological impacts such as host protection, modification of microbial community structure, and regulation of aquatic viral dynamics.
Virophages have been exchanging genes with giant viruses, polintons/Maverick transposons, and eukaryotic genomes for a long time, which helps to diversify mobile elements. Even though cryo-EM, comparative genomics, and metagenomics are giving us more information, we still don't know the answers to some basic questions about the exact GV receptors, the quantitative biophysical affinities, the processes that RNA goes through to mature, and the evolutionary pressures that are causing virophage–GV arms races. This in-depth study shows that virophages play a big role in virus–virus parasitism, microbial ecology, and genome evolution. It also shows that more advanced structural, biochemical, and ecological research is needed.
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References
1. Zhang X, Walker SB, Chipman PR, Nibert ML, Baker TS. Structure of Sputnik, a virophage. Proc Natl Acad Sci U S A. 2012;109(24): 9175–80.
2. Tokarz Deptuła B, Deptuła W, et al. Characteristics of virophages and giant viruses. Acta Biologica Paraninica. 2018;65(4):487–496.
3. Tokarz-Deptuła B, et al. Virophages, satellite viruses, virophage replication and integration: a recent review. Int J Mol Sci. 2024;25(11):5878.
4. Fischer MG. The virophage family Lavidaviridae. Molecular Biology.2018. Vol. 40:171-179. ISBN: 978-1-910190-86-9 (ebook)
5. Duponchel S, Fischer MG. Viva lavidaviruses! Five features of virophages that parasitize giant viruses. PLOS Pathog. 2019;15(11): e1007592.
6. Zhou J, Chen L, Zhang Q, Zhang X, et al. Diversity of virophages in metagenomic data sets. J Virol. 2013;87(14): 8095–8101
7. Ghigo A, et al. The astounding world of glycans from giant viruses. Chem Rev. 2022;122(14): 11011–11034.
8. Levasseur A, Bekliz M, Chabrière E, Pontarotti P, Raoult D. Mavirus-like elements in algal genomes: relics of past virophage–giant virus interactions. Virol J. 2016; 13:118.
9. Rodrigo Araújo Lima Rodrigues, Ludmila Karen dos Santos Silva, Fábio Pio Dornas, Danilo Bretas de Oliveira, Thais Furtado Ferreira Magalhães, Daniel Assis Santos, Adriana Oliveira Costa. Mimivirus Fibrils Are Important for Viral Attachment to the Microbial World by a Diverse Glycoside Interaction Repertoire ASM Journals Journal of Virology. 2015.Vol. 89, No. 23
10. Gaia M, Benamar S, et al. Zamilon, a novel virophage with Mimiviridae host specificity. PLoS One. 2014;9(6): e94923.
11. Mougari S, et al. A virophage cross-species infection through mutant interactions: implications for host-range. mBio/PMC (open access). 2020.
12. Maginnis MS. Virus–receptor interactions: the key to cellular invasion. J Virol. 2018;92(15): e01053-18.
13. Fischer MG, Suttle CA. A virophage at the origin of large DNA transposons. Science. 2011;332(6034):231–4.
14. Roux S, Chan LK, Egan R, Malmstrom RR, McMahon KD, Sullivan MB. Ecogenomics of virophages and their giant virus hosts. Nat Commun. 2017; 8:858.
15. Zhang X, Ng T, Wiessner M, et al. Structure of Sputnik, a virophage, at 3.5-Å resolution. Proc Natl Acad Sci U S A. 2012;109(19):7552–7.
16. Zhang X, Walker SB, Chipman PR, Nibert ML, Baker TS. Structure of Sputnik, a virophage, at 3.5-Å resolution. Proc Natl Acad Sci U S A. 2012;109(5):1545–50.
17. Sun S, Kondabagil K, Gentz PM, Rossmann MG, Rao VB. Structural studies of the Sputnik virophage. J Virol. 2010;84(20):10751–7.
18. Mougari S, Andreani J, Levasseur A, et al. Guarani virophage, a new Sputnik-like isolate from a Brazilian lagoon. Front Microbiol. 2019; 10:1003.
19. La Scola B, Desnues C, Pagnier I, Robert C, Barrassi L, Fournous G, et al. The virophage as a unique parasite of the giant mimivirus. Nature. 2008;455(7209):100–4.
20. Desnues C, Raoult D. Provirophages and transpovirons as the diverse mobilome of giant viruses. Trends Microbiol. 2012;20(10):439–47.
21. Taylor BP, Suttle CA. Ecological effects of virophage with alternative modes. J Virol. 2014;
22. La Scola B, Desnues C, Pagnier I, Robert C, Barrassi L, Fournous G, et al. The virophage as a unique parasite of the giant Mimivirus. Nature. 2008;455(7209):100–4.
23. Gaia M, Peduzzi E, La Scola B. Zamilon, a novel virophage with Mimiviridae host specificity. PLoS One. 2014;9(3): e94923.
24. Fischer MG, Hackl T. Host genome integration and giant virus-induced reactivation of the virophage mavirus. Nature. 2016;540(7634):288–91.
25. La Scola B, Desnues C, Pagnier I, Robert C, Barrassi L, Fournous G, et al. The virophage as a unique parasite of the giant Mimivirus. Nature. 2008;455(7209):100–4.
26. Fischer MG, Hackl T. Virophages and retrotransposons colonize the genomes of eukaryotes. PLoS Pathog. 2021;17(2):e1008554.
27. Zhang X, Walker S, Chipman PR, Nibert ML, Baker TS. Structure of Sputnik, a virophage, at 3.5-Å resolution. Proc Natl Acad Sci U S A. 2012;109(3):1849–54.
28. Tokarz-Deptuła B, Deptuła W, et al. Virophages—Known and Unknown Facts. Viruses (MDPI). 2023;15(6):1321.
29. Fischer MG, Suttle CA. A virophage at the origin of large DNA transposons. Science. 2011;332(6026):231–4.
30. Sun S, et al. Structural studies of the Sputnik virophage. J Virol. 2009;83(14):7335–43.
31. Chen J, et al. Sputnik virophage disrupts the transcriptional regulation of its host giant virus (preprint/2025). J Virol. 2025.
32. Bessenay A, et al. Complex transcriptional regulations of a hyperparasitic virophage and its giant virus. Nat Commun. 2024.
33. Zhang X, et al. Structure of Sputnik, a virophage, at 3.5-Å resolution — full report. PLoS/PNAS (2012).
34. Nino Barreat JG, et al. Ecological and evolutionary dynamics of cell-virus-virophage systems: modeling. PLoS Comput Biol. 2024; (article).
35. Genome integration and reactivation of the virophage mavirus (Fischer et al., 2016 preprint / subsequent reports). bioRxiv / published work (2016).
36. Research and reviews on virophage replication strategies and promoters: Tokarz-Deptuła et al., 2024 review (MDPI).
37. Mougari S, et al. Guarani Virophage, a New Sputnik-Like Isolate from a Brazilian Sample. Front Microbiol. 2019; 10:1003.
38. Reviews on virophage-host translation dependence and lack of translational machinery: multiple comparative genomic analyses
39. Claverie JM, Abergel C. Mimivirus and its virophage. Annu Rev Genet. 2009; 43:49–66.
40. Roux S, Krupovic M, Debroas D, Forterre P, Enault F. Assessment of viral community functional potential from viral metagenomes may be hampered by contamination with cellular sequences. Open Biol. 2013;3(12):130160.
41. Campos RK, Boratto PV, Assis FL, Aguiar ER, Silva LC, Albarnaz JD, et al. Samba virus: a novel mimivirus isolate from a Brazilian lake. Viruses. 2014;6(10):4172–4185.
42. Gaia M, Benamar S, Boughalmi M, Pagnier I, Croce O, Colson P, et al. Zamilon, a novel virophage with Mimiviridae host specificity. Sci Rep. 2014; 4:6822.
43. Levasseur A, Bekliz M, Chabrière E, Pontarotti P, La Scola B. MIMIVIRE is a defence system in mimiviruses that confers resistance to virophage. Nature. 2016;531(7593):249–252.
44. Bekliz M, Colson P, La Scola B. The expanding Mimiviridae family. Virology. 2015; 487:78–90.
45. Krupovic M, Kuhn JH, Fischer MG. A classification system for virophages and satellite viruses. Arch Virol. 2016;161(1):233–247.
46. Yutin N, Raoult D, Koonin EV. Virophages, polintons, and transpovirons: a complex evolutionary network of diverse selfish genetic elements. Virol J. 2013; 10:158.
47. Sun CL, Edwards RA, Rohwer F, Youle M, Blainey PC, Leonard J, et al. Phage particles in microbial communities. Nat Rev Microbiol. 2014;12(7):469–478.
48. Alors M, Gaia M, Pagnier I, et al. Giant virus hosts and virophage interactions: infectivity and co-infection dynamics. Front Microbiol. 2017; 8:132.
49. Desnues C, Boyer M, Raoult D. Sputnik, a virophage infecting the viral domain of life. Adv Virus Res. 2012; 82:63–89.
50. Koonin EV, Yutin N. Evolution of the large nucleocytoplasmic DNA viruses of eukaryotes and convergent origins of viral gigantism. Adv Virus Res. 2010; 78:167–221.
51. Arslan D, Legendre M, Seltzer V, Abergel C, Claverie JM. Distant Mimivirus relative with a larger genome highlights the fundamental features of Megaviridae. Proc Natl Acad Sci U S A. 2011;108(42):17486–17491.
52. Thomas V, Bertelli C, Collyn F, Casson N, Telenti A, Goesmann A, et al. Lausannevirus, a giant amoebal virus encoding histone doublets. Environ Microbiol. 2011;13(6):1454–1466.
53. Kanhayuwa L, Khedkar S, McInerney JO. Novel virophage genomes from metagenomic datasets expand the global distribution of virophages. Front Microbiol. 2016; 7:270.
54. Debat HJ. Giant viruses and their mobile genetic elements: the molecular symphony underlying virophage interactions. Front Microbiol. 2019; 10:2213.
55. Hackl T, et al. Virophages and retrotransposons colonize the genomes of their hosts. eLife. 2021;10: e72674.
56. Chen J, et al. Sputnik virophage disrupts the transcriptional regulation of its giant-virus host. J Virol. 2025;
57. Paez-Espino D, Eloe-Fadrosh EA, Pavlopoulos GA, Thomas AD, Huntemann M, Mikhailova N, et al. Uncovering Earth's virome. Nature. 2016;536(7617):425–430.
58. Yutin N, Koonin EV. Hidden evolutionary complexity of giant viruses and their virophages. Curr Opin Microbiol. 2012;15(5):542–549.
59. Blanc G, Gallot-Lavallée L, Maumus F. Provirophages in the Bigelowiella genome support the existence of an ancient virophage lineage. Virus Evol. 2017;3(2): vex018.
60. Blanc G, et al. Provirophages in the Bigelowiella genome bear testimony to past encounters with giant viruses. Proc Natl Acad Sci U S A. 2015;112(38):E5129–38.
61. Koslová A, et al. Endogenous virophages are active and mitigate giant virus infection. Proc Natl Acad Sci U S A. 2024.
62. Krupovic M, Koonin EV. Self-synthesizing transposons: unexpected key players in the evolution of viruses and defense systems. Curr Opin Microbiol. 2015.
63. Barreat JGN, Bellanger X, et al. A billion-year arms-race between viruses, virophages, and transposable elements. Biol Rev. 2023; (review).
64. Mougari S, Bekliz M, Levasseur A, et al. Virophages of giant viruses: an update at eleven. Viruses. 2019;11(8):733.
65. Raoult D. How the virophage compels the need to readdress viral classification and ecology. Trends Microbiol. 2015; (review).
66. Structural cryo-EM and capsid studies: Zhang et al., 2012; Sun et al., 2009.
67. Desnues C. Sputnik, a virophage infecting the viral domain of life (book chapter/review). In: Current Topics in Virology (2012).
68. Taylor BP, et al. Ecological effects of virophage with alternative modes of transmission. J Theor Biol (2014).
69. Mougari S, Bekliz M, et al. A virophage cross-species infection through mutant expansion and MIMIVIRE manipulation. Commun Biol. 2020;3:
70. Yutin N, Koonin EV. Evolution of virophages from polinton-like viruses and their diversification by gene exchange with giant viruses. Virology. 2013;447(1–2):384–94.
71. Krupovic M, Bamford DH. Virus evolution: how to build a virophage. Nature. 2008;455(7209):119–120.
72. Moreira D, López-García P. Ten reasons to exclude viruses from the tree of life. Nat Rev Microbiol. 2009;7(4):306–311.
73. Villalta L, Schulz F, Roux S. Metagenomic discovery and evolutionary analysis of new virophage lineages across ecosystems. Microbiome. 2023; 11:79. doi:10.1186/s40168-023-01573-1.
74. La Scola B, Desnues C, Pagnier I, Robert C, Barrassi L, Fournous G, et al. The virophage as a unique parasite of the giant mimivirus. Nature. 2008;455(7209):100–104.
75. Fischer MG, Hackl T. Host genome integration and giant virus–induced reactivation of the virophage mavirus. Nature. 2016;540(7632):288–291.
76. Wodarz D. Evolutionary dynamics of giant viruses and their virophages. Ecol Evol. 2013;3(7):2103–2115.
77. “Viruses protect their hosts from other viruses.” Max Planck Institute / press release. 2021 Oct 28.
78. Oh S, Yoo D, Liu W T. “Metagenomics Reveals a Novel Virophage Population in a Tibetan Mountain Lake.” Microbes Environ. 2016; 31:173–177.
79. Paez Espino D, Eloe Fadrosh EA, Pavlopoulos GA, Thomas AD, Huntemann M, Mikhailova N, et al. Diversity, evolution, and classification of virophages uncovered through global metagenomics. Nat Commun. 2019; 10:2321.
80. Desnues C, La Scola B, Yutin N, Fournous G, Robert C, Azza S, et al. Provirophages and transpovirons as the diverse mobilome of giant viruses. Proc Natl Acad Sci U S A. 2012;109(44):18078–18083.
81. eLife Staff / Authors. Virophages and retrotransposons colonize the genomes of a heterotrophic flagellate. eLife. 2021; 10:72674.
82. Ribeiro São-Jóse C, Mello LV, et al. Diversity of virophage signatures in global freshwater systems. ISME J. 2022; 16:1121–34.
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