AEM Accepts, published online ahead of print on 6 November 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01799-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Isolation of Prasinoviruses of the green unicellular algae Ostreococcus spp. at a worldwide geographical scale

Laure Bellec, Nigel Grimsley, and Yves Desdevises^*

UPMC Univ Paris 06, FRE 3247, Observatoire Océanologique, BP44, 66651 Banyuls-sur-Mer, France; CNRS, FRE 3247, Observatoire océanologique, BP44, 66651, Banyuls-sur-Mer, France

^* To whom correspondence should be addressed. Email: desdevises{at}obs-banyuls.fr.

Ostreococcus spp. are extremely small unicellular eukaryotic green algae found worldwide in marine environments, and they are susceptible to attacks by a diverse group of large DNA viruses. Several biologically distinct species of Ostreococcus are known and differ in the ecological niches that they occupy: while O. tauri (representing clade C strains) is found in marine lagoons and coastal seas, strains belonging to clade A, exemplified by O. lucimarinus, are present in different oceans. We used laboratory cultures of clonal isolates of these two species to assay for the presence of viruses in seawater samples from diverse locations. In keeping with the distributions of their host strains, we find a decline in the abundance of O. tauri viruses from a lagoon in South-West France to the Mediterranean Sea, whereas in the ocean no O. tauri viruses were detected. In contrast, viruses infecting O. lucimarinus were detected from distantly separated oceans. DNA sequence, phylogenetic analyses using a conserved viral marker gene, and a Mantel test revealed no relationship between geographic and phylogenetic distances in viruses infecting O. lucimarinus.