L. Scola and B. , A Giant Virus in Amoebae, Science, vol.299, issue.5615, p.1081867, 2003.
DOI : 10.1126/science.1081867

C. Abergel, M. Legendre, and J. M. Claverie, The rapidly expanding universe of giant viruses: Mimivirus, Pandoravirus, Pithovirus and Mollivirus. FEMS microbiology reviews 39, pp.779-796, 2015.

D. Raoult, The 1.2-Megabase Genome Sequence of Mimivirus, Science, vol.306, issue.5700, pp.1344-13501101485, 2004.
DOI : 10.1126/science.1101485

URL : https://hal.archives-ouvertes.fr/hal-00651656

N. Philippe, Pandoraviruses: Amoeba Viruses with Genomes Up to 2.5 Mb Reaching That of Parasitic Eukaryotes, Science, vol.24, issue.17, pp.281-2861239181, 2013.
DOI : 10.1093/nar/24.17.3439

URL : https://hal.archives-ouvertes.fr/cea-00862677

P. Scheid, C. Balczun, and G. A. Schaub, Some secrets are revealed: parasitic keratitis amoebae as vectors of the scarcely described pandoraviruses to humans, Parasitology Research, vol.6, issue.7, pp.3759-3764, 2014.
DOI : 10.1371/journal.pbio.0060114

M. H. Antwerpen, Whole-genome sequencing of a pandoravirus isolated from keratitis-inducing acanthamoeba, Genome announcements, vol.3, pp.136-151, 2015.

M. Legendre, Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology, Proceedings of the National Academy of Sciences, vol.28, issue.10, pp.4274-42791320670111, 2014.
DOI : 10.1093/molbev/msr121

A. Levasseur, Reveals Its Genetic Conservation and Evolution, Genome Biology and Evolution, vol.159, issue.8, pp.2333-2339, 2016.
DOI : 10.1101/gr.074492.107

URL : https://hal.archives-ouvertes.fr/hal-01455587

J. Andreani, Cedratvirus, a Double-Cork Structured Giant Virus, is a Distant Relative of Pithoviruses. Viruses 8, doi:https://doi. org/10, p.8110300, 2016.
URL : https://hal.archives-ouvertes.fr/hal-01453281

N. Zauberman, Distinct DNA Exit and Packaging Portals in the Virus Acanthamoeba polyphaga mimivirus, PLoS Biology, vol.2, issue.5, p.60114, 2008.
DOI : 10.1371/journal.pbio.0060114.sv003

C. Xiao, Cryo-electron Microscopy of the Giant Mimivirus, Journal of Molecular Biology, vol.353, issue.3, pp.493-496060, 2005.
DOI : 10.1016/j.jmb.2005.08.060

C. Xiao, Structural Studies of the Giant Mimivirus, PLoS Biology, vol.50, issue.4, 2009.
DOI : 10.1371/journal.pbio.1000092.g007

J. M. Claverie and C. Abergel, Mimivirus and its virophage Annual review of genetics 43, pp.49-66, 2009.

F. Piacente, Giant DNA virus mimivirus encodes pathway for biosynthesis of unusual sugar 4-amino-4,6-dideoxy-D-glucose (Viosamine) The Journal of biological chemistry 287, pp.3009-3018314559, 2012.

F. Piacente, Characterization of a UDP-N-acetylglucosamine biosynthetic pathway encoded by the giant DNA virus Mimivirus, Glycobiology, vol.287, issue.8, pp.51-61, 2014.
DOI : 10.1074/jbc.M112.342725

Y. Mutsafi, E. Shimoni, A. Shimon, and A. Minsky, Membrane Assembly during the Infection Cycle of the Giant Mimivirus, PLoS Pathogens, vol.6, issue.5, 2013.
DOI : 10.1371/journal.ppat.1003367.s016

T. Ekeberg, Three-Dimensional Reconstruction of the Giant Mimivirus Particle with an X-Ray Free-Electron Laser, Physical Review Letters, vol.73, issue.9, p.98102, 2015.
DOI : 10.1038/355472a0

URL : https://hal.archives-ouvertes.fr/hal-01768282

D. Arslan, M. Legendre, V. Seltzer, C. Abergel, and J. M. Claverie, Distant Mimivirus relative with a larger genome highlights the fundamental features of Megaviridae, Proceedings of the National Academy of Sciences, vol.30, issue.1, pp.17486-174911110889108, 2011.
DOI : 10.1093/nar/30.1.383

N. Yoosuf, Related Giant Viruses in Distant Locations and Different Habitats: Acanthamoeba polyphaga moumouvirus Represents a Third Lineage of the Mimiviridae That Is Close to the Megavirus Lineage, Genome Biology and Evolution, vol.6, issue.12, pp.1324-1330, 2012.
DOI : 10.1186/1743-422X-6-223

R. Grimm, D. Typke, M. Barmann, and W. Baumeister, Determination of the inelastic mean free path in ice by examination of tilted vesicles and automated most probable loss imaging, Ultramicroscopy, vol.63, issue.3-4, pp.169-179, 1996.
DOI : 10.1016/0304-3991(96)00035-6

A. J. Koster, Perspectives of Molecular and Cellular Electron Tomography, Journal of Structural Biology, vol.120, issue.3, pp.276-3083933, 1997.
DOI : 10.1006/jsbi.1997.3933

K. Murata, Whole-cell imaging of the budding yeast Saccharomyces cerevisiae by high-voltage scanning transmission electron tomography, Ultramicroscopy, vol.146, pp.39-45008, 2014.
DOI : 10.1016/j.ultramic.2014.05.008

R. Danev and K. Nagayama, Phase plates for transmission electron microscopy Methods in enzymology 481, pp.343-369, 1016.

K. Murata, Zernike Phase Contrast Cryo-Electron Microscopy and Tomography for Structure Determination at Nanometer and Subnanometer Resolutions, Structure, vol.18, issue.8, pp.903-912006, 2010.
DOI : 10.1016/j.str.2010.06.006

URL : https://doi.org/10.1016/j.str.2010.06.006

R. H. Rochat, Seeing the Portal in Herpes Simplex Virus Type 1 B Capsids, Journal of Virology, vol.85, issue.4, pp.1871-187401663, 2011.
DOI : 10.1128/JVI.01663-10

W. Dai, Zernike phase-contrast electron cryotomography applied to marine cyanobacteria infected with cyanophages, Nature Protocols, vol.82, issue.11, pp.2630-2642, 2014.
DOI : 10.1016/j.jsb.2010.08.004

URL : http://europepmc.org/articles/pmc4371552?pdf=render

W. Dai, Visualizing virus assembly intermediates inside marine cyanobacteria, Nature, vol.25, issue.7473, pp.707-710, 2013.
DOI : 10.1002/jcc.20084

URL : http://europepmc.org/articles/pmc3984937?pdf=render

M. Malac, M. Beleggia, M. Kawasaki, P. Li, and R. F. Egerton, Convenient contrast enhancement by a hole-free phase plate, Ultramicroscopy, vol.118, pp.77-89, 2012.
DOI : 10.1016/j.ultramic.2012.02.004

N. Hosogi, A. Sen, and H. Iijima, Comparison of Cryo TEM Images Obtained with Zernike and Hole-Free Phase Plates, Microscopy and Microanalysis, vol.18, issue.S3, pp.1389-1390, 2015.
DOI : 10.1016/j.ultramic.2012.02.004

R. Danev, B. Buijsse, M. Khoshouei, J. M. Plitzko, and W. Baumeister, Volta potential phase plate for in-focus phase contrast transmission electron microscopy, Proceedings of the National Academy of Sciences, vol.103, issue.6, pp.15635-156401418377111, 2014.
DOI : 10.1021/jp991659y

K. Grunewald, Three-Dimensional Structure of Herpes Simplex Virus from Cryo-Electron Tomography, Science, vol.73, issue.5649, pp.1396-13981090284, 2003.
DOI : 10.1083/jcb.153.6.F25

M. Hayashida and M. Malac, Practical electron tomography guide: Recent progress and future opportunities, Micron, vol.91, pp.49-74010, 2016.
DOI : 10.1016/j.micron.2016.09.010

P. Rez, T. Larsen, and M. Elbaum, Exploring the theoretical basis and limitations of cryo-STEM tomography for thick biological specimens, Journal of Structural Biology, vol.196, issue.3, pp.466-478, 2016.
DOI : 10.1016/j.jsb.2016.09.014

S. G. Wolf, L. Houben, and M. Elbaum, Cryo-scanning transmission electron tomography of vitrified cells, Nature Methods, vol.481, issue.4, pp.423-4282842, 2014.
DOI : 10.1107/S0108767391000375

K. Aoyama, K. Nagano, and K. Mitsuoka, Optimization of STEM imaging conditions for cryo-tomography. Microscopy, 1-5, https, p.3, 2017.

M. Marko, C. Hsieh, R. Schalek, J. Frank, and C. Mannella, Focused-ion-beam thinning of frozen-hydrated biological specimens for cryo-electron microscopy, Nature Methods, vol.12, issue.3, pp.215-217, 2007.
DOI : 10.1111/j.1365-2818.1983.tb04225.x

K. Murata, S. Hagiwara, Y. Kimori, and Y. Kaneko, Ultrastructure of compacted DNA in cyanobacteria by high-voltage cryo-electron tomography Scientific reports 6, p.34934, 2016.

K. Satoh, Effective synaptome analysis of itch-mediating neurons in the spinal cord: A novel immunohistochemical methodology using high-voltage electron microscopy, Neuroscience Letters, vol.599, pp.86-91, 2015.
DOI : 10.1016/j.neulet.2015.05.031

K. Satoh, Three-dimensional visualization of multiple synapses in thick sections using high-voltage electron microscopy in the rat spinal cord, Data in Brief, vol.4, pp.566-570005, 2015.
DOI : 10.1016/j.dib.2015.07.005

T. Malis, S. C. Cheng, and R. F. Egerton, EELS log-ratio technique for specimen-thickness measurement in the TEM, Journal of Electron Microscopy Technique, vol.16, issue.2, pp.193-200, 1988.
DOI : 10.1111/j.1365-2818.1984.tb00489.x

S. Sun, S. Shi, and R. Leapman, Water distributions of hydrated biological specimens by valence electron energy loss spectroscopy, Ultramicroscopy, vol.50, issue.2, pp.127-139, 1993.
DOI : 10.1016/0304-3991(93)90003-G

A. C. Dohnalkova, ABSTRACT, Applied and Environmental Microbiology, vol.77, issue.4, pp.1254-1262, 2011.
DOI : 10.1128/AEM.02001-10

X. Zhang, Three-dimensional structure and function of the Paramecium bursaria chlorella virus capsid, Proceedings of the National Academy of Sciences, vol.73, issue.1, pp.14837-148421107847108, 2011.
DOI : 10.1006/jsbi.1999.4174

J. R. Kremer, D. N. Mastronarde, and J. Mcintosh, Computer Visualization of Three-Dimensional Image Data Using IMOD, Journal of Structural Biology, vol.116, issue.1, pp.71-760013, 1996.
DOI : 10.1006/jsbi.1996.0013

T. Science and . Of-japan, grant Number 17H05825) and the Collaborative Study Program of National Institute for Physiological Sciences (to K.O., grant Number: 2016- No. 38), the CNRS

A. Contributions, J. H. , C. A. , K. O. , J. M. Conceived-the-experiment et al., isolated the virus and provided samples performed the cryo-tomography studies, M. analysed the data. All authors read and approved the final manuscript