Marine Prasinovirus Genomes Show Low Evolutionary Divergence and Acquisition of Protein Metabolism Genes by Horizontal Gene Transfer

Abstract

Although marine picophytoplankton are at the base of the global food chain, accounting for half of the planetary primary production, they are outnumbered 10 to 1 and are largely controlled by hugely diverse populations of viruses. Eukaryotic microalgae form a ubiquitous and particularly dynamic fraction of such plankton, with environmental clone libraries from coastal regions sometimes being dominated by one or more of the three genera Bathycoccus, Micromonas, and Ostreococcus (class Prasinophyceae). The complete sequences of two double-stranded (dsDNA) Bathycoccus, one dsDNA Micromonas, and one new dsDNA Ostreococcus virus genomes are described. Genome comparison of these giant viruses revealed a high degree of conservation, both for orthologous genes and for synteny, except for one 36-kb inversion in the Ostreococcus lucimarinus virus and two very large predicted proteins in Bathycoccus prasinos viruses. These viruses encode a gene repertoire of certain amino acid biosynthesis pathways never previously observed in viruses that are likely to have been acquired from lateral gene transfer from their host or from bacteria. Pairwise comparisons of whole genomes using all coding sequences with homologous counterparts, either between viruses or between their corresponding hosts, revealed that the evolutionary divergences between viruses are lower than those between their hosts, suggesting either multiple recent host transfers or lower viral evolution rates.

Host-derived viral transporter protein for nitrogen uptake in infected marine phytoplankton

“…Phycodnaviridae infect a broad range of eukaryotic algae (38). To date, 12 genome sequences of viruses infecting the prasinophyte alga Ostreococcus-a widely distributed marine Mamiellophyceae (39,40) and the smallest known free-living eukaryotic cell-are available (41)(42)(43)(44)(45)(46). These include viruses that infect one of three species: O. tauri, Ostreococcus lucimarinus, and Ostreococcus mediterraneus.…”

Potassium Ion Channels: Could They Have Evolved from Viruses?

“…(Moreau et al, 2010). To our knowledge, K + channel-encoding proteins have only been reported in DNA viruses that infect algae.…”

“…Viruses from several other genera in the phycodnavirus family have been sequenced, and members from two of them encode K + channel proteins, including viruses that infect the filamentous brown alga Ectocarpus siliculosus (Delaroque et al, 2001) and viruses that infect some of the smallest known algae (the Prasinophytes), Ostreococcus (Derelle et al, 2008;Weynberg et al, 2009), Micromonas (Moreau et al, 2010), and Bathycoccus spp. (Moreau et al, 2010).…”

Diversity of Viruses Infecting the Green Microalga Ostreococcus lucimarinus

“…More specifically, it is unclear whether diversity is connected to geographical distance and whether differential infection and lysis patterns exist among such viruses that infect the same host strain. Prasinophyte/prasinovirus systems offer powerful models, because the hosts (prasinophyte algae) are relatively well characterized and because many lytic viruses presenting various host specificities have been isolated on these algae (1,(16)(17)(18)(19)(20)(21). The prasinophytes and, more specifically, members of the class Mamiellophyceae represent an ecologically important group of unicellular green algae that are found in the euphotic zone of many marine settings (22).…”