Viruses exist wherever life is found. They are a major cause of mortality, a driver of global geochemical cycles and a reservoir of the greatest genetic diversity on Earth.
Marine viruses range from 20 – 650nm in size and consist of nucleic acid surrounded by a protein coat. Viruses are incapable of independent metabolism, so to grow and replicate they have to ‘hijack’ biosynthetic machinery of host cell.
The total viral abundance appears to be higher than total prokaryotic abundance. Virus-induced mortality of prokaryotes varies strongly on a temporal and spatial scale and shows that phages can be important predators of bacterioplankton. However, viral diseases cause mortality in all kinds of organisms, from bacteria to whales. This mortality and the release of cell lysis products into the environment can strongly influence microbial food web processes and biogeochemical cycles. In fact, viruses are responsible for 10-50% of mortality of heterotrophic marine bacteria and may be more important in regulating bacterial communities than grazing by flagellates.
The majority of viral infection in marine systems appears to occur via active virions and lytic cycle. They have a tremendous potential impact on biological oceanographic processes, including material & energy flow as well as plankton diversity. A considerable amount of work has been done on viruses, which infect various important species, Emiliania huxleyi and Synechococcus sp (mid-ocean cyanobacteria).
More than one million of viral organisms are thought to exist in every milliliter of seawater. These microscopic individuals, which cannot even survive on their own, impact strongly on almost every process of the ocean. From evolution drivers, to food releasers, viruses have an enormous set of roles that we have only just started to understand.