Marine Prasinoviruses and Their Tiny Plankton Hosts: A Review

Abstract

Viruses play a crucial role in the marine environment, promoting nutrient recycling and biogeochemical cycling and driving evolutionary processes. Tiny marine phytoplankton called prasinophytes are ubiquitous and significant contributors to global primary production and biomass. A number of viruses (known as prasinoviruses) that infect these important primary producers have been isolated and characterised over the past decade. Here we review the current body of knowledge about prasinoviruses and their interactions with their algal hosts. Several genes, including those encoding for glycosyltransferases, methyltransferases and amino acid synthesis enzymes, which have never been identified in viruses of eukaryotes previously, have been detected in prasinovirus genomes. The host organisms are also intriguing; most recently, an immunity chromosome used by a prasinophyte in response to viral infection was discovered. In light of such recent, novel discoveries, we discuss why the cellular simplicity of prasinophytes makes for appealing model host organism-virus systems to facilitate focused and detailed investigations into the dynamics of marine viruses and their intimate associations with host species. We encourage the adoption of the prasinophyte Ostreococcus and its associated viruses as a model host-virus system for examination of cellular and molecular processes in the marine environment.

Keywords: marine virus ecology; virus-driven evolution; virus–host interactions.

Figure 1

Negatively stained transmission electron microscopy micrographs of (A,B) Micromonas pusilla viruses (MpVs); (C) ‘Spiderweb’-like plate from exterior of Bathycoccus prasinos cell; (D–H) O. tauri viruses (OtVs).

Figure 2

Characterisation of the OtV-2 virally encoded cytochrome b₅ protein. Absorbance spectra for oxidised and reduced forms of (A) human cytochrome b₅ protein and (B) OtV-2 viral cytochrome b₅ protein and (C) structural display of the OtV-2 protein as a ribbon diagram. Adapted from [37].