Nature 461, 258-262 (10 September 2009) | doi:10.1038/nature08284; Received 14 June 2009; Accepted 9 July 2009; Published online 26 August 2009

Photosystem I gene cassettes are present in marine virus genomes

Itai Sharon1,2,9, Ariella Alperovitch1,9, Forest Rohwer4,5, Matthew Haynes4, Fabian Glaser3, Nof Atamna-Ismaeel1, Ron Y. Pinter2, Frédéric Partensky6, Eugene V. Koonin7, Yuri I. Wolf7, Nathan Nelson8 & Oded Béjà1

  1. Faculty of Biology,
  2. Faculty of Computer Science,
  3. Bioinformatics Knowledge Unit, Lorry I. Lokey Interdisciplinary Center for Life Sciences and Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel
  4. Department of Biology,
  5. Center for Microbial Sciences, San Diego State University, San Diego, California 92182, USA
  6. CNRS and UPMC-Université Paris 6 (UMR 7144), Station Biologique, 29682 Roscoff, France
  7. National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland 20894, USA
  8. Department of Biochemistry, George S. Wise Faculty of Life Sciences, Daniella Rich Institute for Structural Biology, Tel Aviv University, Tel Aviv 69978, Israel
  9. These authors contributed equally to this work.

Correspondence to: Oded Béjà1 Correspondence and requests for materials should be addressed to O.B. (Email: beja@tx.technion.ac.il).

Cyanobacteria of the Synechococcus and Prochlorococcus genera are important contributors to photosynthetic productivity in the open oceans1, 2, 3. Recently, core photosystem II (PSII) genes were identified in cyanophages and proposed to function in photosynthesis and in increasing viral fitness by supplementing the host production of these proteins4, 5, 6, 7. Here we show evidence for the presence of photosystem I (PSI) genes in the genomes of viruses that infect these marine cyanobacteria, using pre-existing metagenomic data from the global ocean sampling expedition8 as well as from viral biomes9. The seven cyanobacterial core PSI genes identified in this study, psaA, B, C, D, E, K and a unique J and F fusion, form a cluster in cyanophage genomes, suggestive of selection for a distinct function in the virus life cycle. The existence of this PSI cluster was confirmed with overlapping and long polymerase chain reaction on environmental DNA from the Northern Line Islands. Potentially, the seven 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 might provide a unique way of funnelling reducing power from respiratory and other electron transfer chains to the PSI.


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