Virocell Concept, The

Abstract

Viruses have been historically defined as viral particles (virions). The virocell concept has been proposed to put instead emphasis on the intracellular cycle of virus reproduction. In that view, viral infection transforms the infected cells (either a bacterium, an archaeon or a eukaryote) into a novel type of cellular organism, a virocell, whose aim is to produce virions. The virocell concept has several implications for the question of the origin and nature of viruses. It emphasises that viruses originated after ribosomeā€encoding cells (ribocells) and can be considered as bona fide, cellular, living organisms. Notably, the virocell concept helps to realise that novel proteins could originate in two different cellular contexts (either ribocell or virocell) during genome replication/recombination. Considering the diversity, ubiquity and abundance of viruses, a huge proportion of proteins in the biosphere have therefore probably a bona fide viral origin. Many of them were later on transferred to genomes of ribocells by viral/plasmid integrations. The concept of virocell thus helps to understand the fundamental role that viruses have played in biological evolution.

Key Concepts:

  • Virocells correspond to infected cells producing virons.

  • Ribovirocell are Infected cells that produce virions but can still divide.

  • The virus is a living entity during the intracellular phase of its life cycle.

  • Different organisms (archaea, bacteria, eucaryote or virus) can share the same cell, each one being defined by its own evolutionary trajectory.

  • The ancestors of modern viruses appeared after the invention of the ribosome and modern proteins but before the divergence of modern cells from their last common ancestor.

  • Viruses are a huge source of new genes that originated during replication/recombination of viral genomes.

Keywords: virocell; ribocell; ribovirocell; virus; virion; lysogeny; bacteriophage; viral factory; Mimivirus

Figure 1.

Origin and evolution of concepts on the nature of viruses.

Figure 2.

Schematic representation of the transformation of a ribocell (in that case a bacterium) into a virocell by a head and tailed virus (Caudovirales). In that example, the bacterial DNA has been completely destroyed and replaced by viral DNA. The only active genome in the infected cell is the viral one. The infected cell is still a cell but cannot be anymore considered to be a bacterium. The virocell is the cradle for the emergence of new specific viral genes.

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Further Reading

Forterre P (2008) Origin of viruses. In: Mahy BWJ and Van Regenmortel MHV (eds) Encyclopedia of Virology, vol 5. Oxford: Elsevier.

Forterre P (2009) Evolution, viral. In: Moselio S (ed.) The Encyclopedia of Microbiology, 3rd edn, pp. 370–389 Amsterdam: Elsevier.

Ryan RF (2009) Virolution. United Kingdom: Harper Collins.

Villarreal LP (2005) Viruses and the Evolution of Life. Washington: ASM Press.

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Patrick, Forterre(Jul 2012) Virocell Concept, The. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0023264]