IntroductionViruses are the most abundant organisms in the sea, with approximately ten billion in every liter of seawater(1, 2). Viruses are very small, generally 20-200 nm, and have a simple structure consisting of genetic material with a protein coat and sometimes a lipid envelope(2). Because of their simplicity, viruses rely on exploiting living cells and using the host's cellular machinery to replicate (3). Regardless of their size, viruses have been found to have a significant influence on many ecological processes and biogeochemical cycles in marine ecosystems ( 2 , 4 ). Studies suggest that viruses contribute to nutrient recycling through infection and lysis of marine microorganisms, which in turn control the composition and diversity of microbial communities in marine environments ( 1 , 5 ). Genes involved in photosynthesis have also been found in viral genomes, leading researchers to believe that proteins involved in bacterial photosynthesis originate from bacteriophages, viruses that infect bacteria (6, 7). Research on marine viruses is important because it allows us to gain a deeper understanding of ocean ecology and the driving forces of marine and global ecosystems (8). DiscussionEvery second, approximately 1023 viral infections occur in the ocean(8). These infections influence the mortality of marine organisms and are consequently a major force underlying global geochemical cycles and the structure of microbial populations and communities ( 4 , 5 , 8 ). Microorganisms constitute 90% of the living biomass in the sea and it is estimated that 20% of this biomass is eliminated every day by viruses (8). Viruses influence the mortality of bacteria in the ocean and thus regulate both bacterial populations and subsequent...... middle of paper ......olonen AC, Rohwer F, Chisholm SW. 2004. Transfer of photosynthesis genes to and from Prophylococcus viruses. Proceedings of the National Academy of Sciences of the United States of America 101:11013-11018.17. Lindell D, Jaffe JD, Johnson ZI, Church GM, Chisholm SW. 2005. Photosynthesis genes in marine viruses produce proteins during host infection. Nature 438:86-89.18. Mann NH, Clokie MR, Millard A, Cook A, Wilson WH, Wheatley PJ, Letarov A, Krisch HM. 2005. The genome of S-PM2, a T4-type “photosynthetic” bacteriophage that infects marine strains of Synechococcus. Journal of Bacteriology 187:3188-3200.19. Brussaard CPD, Wilhelm SW, Thingstad F, Weinbauer MG, Bratbak G, Heldal M, Kimmance SA, Middelboe M, Nagasaki K, Paul JH, Schroeder DC, Suttle CA, Vaque D, Wommack KE. 2008. Global-scale processes with a nanoscale unit: the role of marine viruses. ISME J 2:575-578.