1. ¹Faculty of Biology, Technion—Israel Institute of Technology, Haifa, Israel
2. ²Faculty of Computer Science, Technion—Israel Institute of Technology, Haifa, Israel
3. ³Inter-Departmental Program for Biotechnology, Technion—Israel Institute of Technology, Haifa, Israel
4. ⁴J Craig Venter Institute, Rockville, MD, USA
5. ⁵The Lorry I Lokey Interdisciplinary Center for Life Sciences and Engineering, Technion—Israel Institute of Technology, Haifa, Israel
6. ⁶Center for Research on Biological Clocks, Texas A&M University, College Station, TX, USA
7. ⁷Schulich Faculty of Chemistry, Technion—Israel Institute of Technology, Haifa, Israel
8. ⁸School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel

Correspondence: O Béjà, Faulty of Biology, Technion—Israel Institute of Technology, Haifa 32000, Israel. E-mail: beja@tx.technion.ac.il

⁹These authors contributed equally to this work.

Received 9 May 2007; Accepted 3 July 2007; Published online 9 August 2007.

Abstract

Cyanobacteria of the genera Synechococcus and Prochlorococcus are important contributors to photosynthetic productivity in the open ocean. The discovery of genes (psbA, psbD) that encode key photosystem II proteins (D1, D2) in the genomes of phages that infect these cyanobacteria suggests new paradigms for the regulation, function and evolution of photosynthesis in the vast pelagic ecosystem. Reports on the prevalence and expression of phage photosynthesis genes, and evolutionary data showing a potential recombination of phage and host genes, suggest a model in which phage photosynthesis genes help support photosynthetic activity in their hosts during the infection process. Here, using metagenomic data in natural ocean samples, we show that about 60% of the psbA genes in surface water along the global ocean sampling transect are of phage origin, and that the phage genes are undergoing an independent selection for distinct D1 proteins. Furthermore, we show that different viral psbA genes are expressed in the environment.