Organisms from all domains of life are subject to viral infection, whether tobacco plants, flying tropical insects or archaea in the hot springs of Yellowstone National Park. However, it appears that it is those viruses that attack bacteria (i.e. so called bacteriophages – literally, bacteria eater – see Figure 1) that are the most abundant of all with these viruses present in huge numbers (BNID 104839, 104962, 104960) in a host of different environments ranging from soils to the open ocean.
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Figure 2: Structures of viral capsids. The regularity of the structure of viruses has enabled detailed, atomic-level analysis of their construction patterns. This gallery shows a variety of the different geometries explored by the class of nearly spherical viruses. HIV and influenza figures are 3D renderings of virions from the tomogram..(Symmetric virus structures adapted from T. S. Baker et al., Microbiol. Mol. Biol. Rev. 63:862, 1999. HIV structure adapted from J. A. G. Briggs et al., Structure 14:15, 2006 and influenza virus structure adapted from A. Harris, Proceedings of the National Academy of Sciences, 103:19123, 2006.)

As a result of their enormous presence on the biological scene, viruses play a role not only in the health of their hosts, but in global geochemical cycles affecting the availability of nutrients across the planet. For example, it has been estimated that as much as 20% of the bacterial mass in the ocean is subject to viral infection every day (BNID 106625). This can strongly decrease the flow of biomass to higher trophic levels that feed on prokaryotes (BNID 104965). //

• porcine circovirus (PCV) = 17nm (0.017 micron)
• polio virus = 30nm
• HIV-1 = 120nm
• pandora virus = 500nm (0.5 micron)