Photosystem I gene cassettes are present in marine virus genomes

Abstract

Cyanobacteria of the Synechococcus and Prochlorococcus genera are important contributors to photosynthetic productivity in the open oceans1-3. Here, using pre-existing metagenomic datasets from the global ocean sampling (GOS) expedition4 as well as from viral biomes5, we show the first evidence for the presence of photosystem I (PSI) genes in genomes of marine viruses that infect these marine cyanobacteria. Recently, core photosystem II (PSII) genes were identified in cyanophages; they were proposed to be functional in photosynthesis and in increasing viral fitness by supplementing the host production of these proteins6-9. The 7 cyanobacterial core PSI genes identified in this study, psaA, B, C, D, E, K and a unique J and F fusion, form a distinctive cluster in cyanophage genomes, suggestive of selection for a distinct function in virus life cycle. The existence of this PSI cluster was confirmed with overlapping and long PCR performed on environmental DNA from the Northern Line Islands. Potentially, the 7 proteins encoded by the viral genes are sufficient to form an intact monomeric PSI complex. Projection of viral predicted peptides on the cyanobacterial PSI crystal structure10 suggested that the viral-PSI components may provide a unique way of funneling reducing power from respiratory and other electron transfer chains to PSI.

Depth-stratified functional and taxonomic niche specialization in the ‘core’ and ‘flexible’ Pacific Ocean Virome

“…AMGs have also been observed in other cultivated viral isolates including genes for sugar metabolism, lipid-fatty acid metabolism and signalling (Derelle et al, 2008). Further, culture-independent metagenomic surveys have identified additional AMGs involved in motility, anti-oxidation, photosystem I, energy metabolism and iron-sulphur clusters (Yooseph et al, 2007;Dinsdale et al, 2008;Sharon et al, 2009Sharon et al, , 2011, with recent, focused pathway analysis expanding these ocean virus-encoded AMG lists to include nearly all of central carbon metabolism .…”

Four Central Points About Coevolution

“…The genes for photosynthesis in these species show evidence of repeated transfer back and forth between the cyanobacterial genome and the genomes of the viruses with which they coevolve (Lindell et al 2004(Lindell et al , 2007. The result is a complex distribution of genes for photosynthesis among these coevolving, and ecologically important, hosts and viruses (Sharon et al 2009). …”

Modulation of host ROS metabolism is essential for viral infection of a bloom-forming coccolithophore in the ocean

“…Thus, viruses have a huge impact on ocean biogeochemical cycles by short-circuiting the flux of carbon and nutrients from phytoplankton and bacteria to higher trophic levels, shunting it to the pool of dissolved and particulate organic matter, and making it more available for recycling by microbial respiration (Fuhrman, 1999;Wilhelm and Suttle, 1999;Suttle, 2007). Marine viruses are known to regulate phytoplankton population size, distribution and composition by eliminating more dominant phytoplankton species and are considered major vehicles for horizontal gene transfer between distantly related species (Lindell et al, 2005;Suttle, 2005;Rohwer and Thurber, 2009;Sharon et al, 2009;Winter et al, 2010;Breitbart, 2012).…”