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[14] [15] Marine viruses, although microscopic and essentially unnoticed by scientists until recently, are the most abundant and diverse biological entities in the ocean. Viruses have an estimated abundance of 10 30 in the ocean, or between 10 6 and 10 11 viruses per millilitre. [4]
The two main hypotheses for their origin are that either they evolved from small viruses, picking up DNA from host organisms, or that they evolved from very complicated organisms into the current form which is not self-sufficient for reproduction. [58] What sort of complicated organism giant viruses might have diverged from is also a topic of ...
Phycodnaviridae is a family of large (100–560 kb) double-stranded DNA viruses that infect marine or freshwater eukaryotic algae. Viruses within this family have a similar morphology, with an icosahedral capsid (polyhedron with 20 faces). As of 2014, there were 33 species in this family, divided among 6 genera.
The tiny (0.6 μm) marine cyanobacterium Prochlorococcus, discovered in 1986, forms today an important part of the base of the ocean food chain and accounts for much of the photosynthesis of the open ocean [84] and an estimated 20% of the oxygen in the Earth's atmosphere. [85]
Viruses are found wherever there is life and have probably existed since living cells first evolved. [106] The origin of viruses is unclear because they do not form fossils, so molecular techniques have been used to compare the DNA or RNA of viruses and are a useful means of investigating how they arise. [107]
The high density of viruses and therefore of viral production (in comparison to surrounding deep-sea waters) implies that viruses are a significant source of microbial mortality at the vents. [33] As in other marine environments, deep-sea hydrothermal viruses affect the abundance and diversity of prokaryotes and therefore impact microbial ...
[38] [4] They can withstand temperatures ranging from 12 to 30 °C and salinities of 18-70 ppt. [4] The DNA of cyanophages is susceptible to UV degradation but can be restored in host cells through a process called "photoreactivation". [39] The viruses cannot move independently and must rely on currents, mixing, and host cells to transport them.
Very little is known about the microbial community of the mesopelagic zone because it is a difficult part of the ocean to study. Recent work using DNA from seawater samples emphasized the importance of viruses and microbes role in recycling organic matter from the surface ocean, known as the microbial loop.