Several studies reported on a handful of cases of functional mimicry by viral proteins [20] . In few cases, evidence for gene transfer from the host to the virus is obvious. For example, the photosynthetic efficiency in cyanobacteria (Synechococcus and Prochlorococcus) relies on components of the photosystem II. These critical components express in the respective phages [21] . In the case of the phytoplankton-virus system, the DNA virus EhV that infects the microalge (Emiliania huxleyi), contains a complete metabolic pathway as a result of a horizontal gene transfer [22] . A similar case is demonstrated for the dUTPase genes (Dut) that are necessary for regulating the cellular levels of dUTP. Phylogenetic analysis revealed the origin of the viral Dut sequence in a monophyletic cluster of DNA viruses with eukaryotic hosts [23] .