title: Genome sequence of Ostreococcus tauri virus OtV-2 throws light on the role of picoeukaryote niche separation in the ocean.
abstract: Ostreococcus tauri, a unicellular marine green alga, is the smallest known free-living eukaryote and is ubiquitous in the surface oceans. The ecological success of this organism has been attributed to distinct low- and high-light-adapted ecotypes existing in different niches at a range of depths in the ocean. Viruses have already been characterized that infect the high-light-adapted strains. Ostreococcus tauri virus (OtV) isolate OtV-2 is a large double-stranded DNA algal virus that infects a low-light-adapted strain of O. tauri and was assigned to the algal virus family Phycodnaviridae, genus Prasinovirus. Our working hypothesis for this study was that different viruses infecting high- versus low-light-adapted O. tauri strains would provide clues to propagation strategies that would give them selective advantages within their particular light niche. Sequence analysis of the 184,409-bp linear OtV-2 genome revealed a range of core functional genes exclusive to this low-light genotype and included a variety of unexpected genes, such as those encoding an RNA polymerase sigma factor, at least four DNA methyltransferases, a cytochrome b(5), and a high-affinity phosphate transporter. It is clear that OtV-2 has acquired a range of potentially functional genes from its host, other eukaryotes, and even bacteria over evolutionary time. Such piecemeal accretion of genes is a trademark of large double-stranded DNA viruses that has allowed them to adapt their propagation strategies to keep up with host niche separation in the sunlit layers of the oceanic environment.
authors.affiliation: Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, United Kingdom.
authors.forename: Karen D
authors.initials: KD
authors.lastname: Weynberg
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Allen
authors.forename: Ilana C
authors.initials: IC
authors.lastname: Gilg
authors.forename: David J
authors.initials: DJ
authors.lastname: Scanlan
authors.forename: William H
authors.initials: WH
authors.lastname: Wilson
mesh_terms: D000220:Adaptation, Biological; D000460:Chlorophyta / Q000821:virology*; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D005814:Genes, Viral; D016679:Genome, Viral; D008969:Molecular Sequence Data; D009792:Oceans and Seas; D017862:Phycodnaviridae / Q000235:genetics* / Q000302:isolation & purification; D017422:Sequence Analysis, DNA
chemical_list: D004279:DNA, Viral