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PhotoPhage Report Summary

Project ID: 321647
Funded under: FP7-IDEAS-ERC
Country: Israel

Final Report Summary - PHOTOPHAGE (The role of viral photosynthetic proteins in oceanic photosynthesis)

Marine photosynthesis is one of the major contributors to the global carbon cycle and the world’s oxygen supply. This process is largely driven by cyanobacteria, namely Synechococcus and Prochlorococcus. Genes encoding photosystem-II (PSII) reaction center proteins are found in many cyanophage genomes, and are expressed during the infection of their hosts. On the basis of metagenomics, cyanophage photosystem-I (PSI) gene cassettes were recently discovered with two gene arrangements psaJF-C-A-B-K-E-D and psaD-C-A-B. It was suggested that the horizontal transfer of PSII and PSI genes is increasing phage fitness.

The main purpose of the PhotoPhage project is to learn about viral ‘photosynthesis’ using environmental as well as lab-based experiments. Using samples from around the globe we were able to learn about the huge diversity of the viral PSI genes and to draw their distribution pattern. The viral genes were found in the Pacific, Atlantic and Indian Oceans and were confined to a strip along the equator. In addition we found that the photosynthetic genes on the two different gene clusters are encoding for structurally different proteins. This implies for different mechanistic modes of photosynthesis.

Our wet-lab experiments show that when phages that carry both PSI and PSII genes are infecting cyanobacteria, they express their photosynthetic genes and the viral proteins are entering in the host membranes. The infected cells keep performing photosynthesis during the entire period of infection and enhance cyclic photosynthesis. Thus keep harvesting light energy while infected and probably using this excess energy to produce more phage progeny.

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