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The viriosphere: which importance in the functioning and evolution of aquatic ecosystems? Volume 13, issue 3, mai-juin 2009

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Authors
Inra, UMR CARRTEL, Station d’hydrobiologie lacustre, Équipe BioFEEL, 75, avenue de Corzent, 74203 Thonon-les-Bains Cedex

The mean abundance of viruses in aquatic ecosystems is about 10 7 per mL, what leads to the estimation that there are approximately 10 30 viruses in these systems on earth. These viruses, which are mainly bacteriophages, i.e. viruses infecting prokaryotes, constitute a very dynamical and diverse biological compartment, although still little is known on their ecology in both marine and limnetic systems. Aquatic viral ecology is indeed a relatively recent topic of aquatic sciences. Each day, 10 29 viral infections are likely to occur in the ocean and these infections are probably the main cause of microbial mortality. They may also be responsible for the modification and the diversification of the bacterial community structure. Viral lysis is also proposed as a main driving force in the global biogeochemical cycles in the ocean, with the estimated release of 10 9 tons of carbon per day, a process largely ignored until recently especially when one refers to the modelisation of the ocean functioning or the coupling between the ocean and the atmosphere. Viruses are thus a main actor of ecosystem functioning with multiple potential roles and this is the reason why they interest more and more ecologists, evolutionists or scientists looking for potential therapeutic agents. In the first part of this review, the focus is made on abundance, dynamics and diversity of aquatic viruses and their role as mortality agents of planktonic populations.