Characterization of Mollivirus kamchatka , the first modern representative of the proposed Molliviridae family of giant viruses.

• Main Authors: Christo-Foroux, Eugene, Alempic, Jean-Marie, Lartigue, Audrey, Santini, Sébastien, Labadie, Karine, Legendre, Matthieu, Abergel, Chantal, Claverie, Jean-Michel
• Other Authors: Information génomique et structurale (IGS), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS), Institut de Biologie François JACOB (JACOB), Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Institut de Microbiologie de la Méditerranée (IMM)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDV.MP.VIR]Life Sciences [q-bio]/Microbiology and Parasitology/Virology; Kamchatka; permafrost; Subarctic
• Online Access: https://amu.hal.science/hal-02464533; https://amu.hal.science/hal-02464533/document; https://amu.hal.science/hal-02464533/file/molliEugene.pdf; https://doi.org/10.1101/844274

International audience Microbes trapped in permanently frozen paleosoils (permafrost) are the focus of increasing researches in the context of global warming. Our previous investigations led to the discovery and reactivation of two Acanthamoeba-infecting giant viruses, Mollivirus sibericum and Pithovirus sibericum from a 30,000-year old permafrost layer. While several modern pithovirus strains have since been isolated, no contemporary mollivirus relative was found. We now describe Mollivirus kamchatka, a close relative to M. sibericum, isolated from surface soil sampled on the bank of the Kronotsky river in Kamchatka. This discovery confirms that molliviruses have not gone extinct and are at least present in a distant subarctic continental location. This modern isolate exhibits a nucleo-cytoplasmic replication cycle identical to that of M. sibericum Its spherical particle (0.6-μm in diameter) encloses a 648-kb GC-rich double stranded DNA genome coding for 480 proteins of which 61 % are unique to these two molliviruses. The 461 homologous proteins are highly conserved (92 % identical residues in average) despite the presumed stasis of M. sibericum for the last 30,000 years. Selection pressure analyses show that most of these proteins contribute to the virus fitness. The comparison of these first two molliviruses clarify their evolutionary relationship with the pandoraviruses, supporting their provisional classification in a distinct family, the Molliviridae, pending the eventual discovery of intermediary missing links better demonstrating their common ancestry.Importance Virology has long been viewed through the prism of human, cattle or plant diseases leading to a largely incomplete picture of the viral world. The serendipitous discovery of the first giant virus visible under light microscopy (i.e., >0.3μm in diameter), mimivirus, opened a new era of environmental virology, now incorporating protozoan-infecting viruses. Planet-wide isolation studies and metagenomes analyses have shown the presence of giant ...