Les virus au service de l'écologie marine.

In less than 50 years, marine viruses shifted from meaningless entities to major players of the oceanic ecosystems. These parasites numerically dominate marine microbial communities and mostly infect micro-organisms (bacteria, microalgae and other protists) that constitute the basis of trophic levels in the ocean. Viruses that replicate though a lysogenic cycle affect genetic expression of the host and promote horizontal gene transfer within the marine microbial communities. Viruses that replicate through a lytic cycle contribute to the control of host population and the release of a large amount of organic matter in the ocean. From the genetic manipulation of their hosts to the modification of the biogeochemical cycles, the marine viruses play a pivotal role for the structure and the functioning of their environment and cannot be excluded from ecological models anymore. This review presents the impact of viruses on the marine environment by focusing on three integration scales: the cell, the community and the ecosystem.