Virosphere
Virosphere (virus diversity, virus world, global virosphere) was coined to refer to all those places in which viruses are found or which are affected by viruses.[1][2] However, more recently virosphere has also been used to refer to the pool of viruses that occurs in all hosts and all environments,[3] as well as viruses associated with specific types of hosts (prokaryotic virosphere,[4] archaeal virosphere,[5] Invertebrate virosphere),[6] type of genome (RNA virosphere,[7] dsDNA virosphere)[8] or ecological niche (marine virosphere).[9]
Viral genome diversity
The scope of viral genome diversity is enormous compared to cellular life. Cellular life including all known organisms have double stranded DNA genome. Whereas viruses have one of at least 7 different types of genetic information, namely dsDNA, ssDNA, dsRNA, ssRNA+, ssRNA-, ssRNA-RT, dsDNA-RT. Each type of genetic information has its specific manner of mRNA synthesis. Baltimore classification is a system providing overview on these mechanisms for each type of genome. Moreover, in contrast to cellular organisms, viruses don't have universally conserved sequences in their genomes to be compared by.[citation needed]
Viral genome size varies approximately 1000 fold. Smallest viruses may consist of only from 1–2 kb genome coding for 1 or 2 genes and it is enough for them to successfully evolve and travel through space and time by infecting and replicating (make copies of their own) in its host. Two most basic viral genes are
Viral host diversity
Viruses are cosmopolites, they are able to infect every cell and every organism on planet earth. However different viruses infect different hosts. Viruses are host specific as they need to replicate (reproduce) within a host cell. In order to enter the cell viral particle needs to interact with a receptor on the surface of its host cell. For the process of replication many viruses use their own replicases, but for protein synthesis they are dependent on their host cell protein synthesis machinery. Thus, host specificity is a limiting factor for viral reproduction.[citation needed]
Some viruses have extremely narrow host range and are able to infect only 1 certain strain of 1 bacterial species, whereas others are able to infect hundreds or even thousands of different hosts. For example cucumber mosaic virus (CMV) can use more than 1000 different plant species as a host.[13] Members of viral families like Rhabdoviridae infect hosts from different kingdoms e.g. plants and vertebrates.[14] And members of genera Psimunavirus and Myohalovirus infect hosts from different domains of life e.g. bacteria and archaea.[15]
Viral capsid diversity
Capsid is the outer protecting shell or scaffold of a viral genome. Capsid enclosing viral nucleic acid make up viral particle or a virion. Capsid is made of protein and sometimes has lipid layer harboured from the host cell while exiting it. Capsid proteins are highly symmetrical and assemble within a host cell by their own due to the fact, that assembled capsid is more thermodynamically favourable state, than separate randomly floating proteins. The most viral capsids have icosahedral or helical symmetry, whereas bacteriophages have complex structure consisting of icosahedral head and helical tail including baseplate and fibers important for host cell recognition and penetration.[16] Viruses of archaea infecting hosts living in extreme environments like boiling water, highly saline or acidic environments have totally different capsid shapes and structures. The variety of capsid structures of Archaeal viruses includes lemon shaped viruses Bicaudaviridae of family and Salterprovirus genus, spindle form Fuselloviridae, bottle shaped Ampullaviridae, egg shaped Guttaviridae.[5]
Capsid size of a virus differs dramatically depending on its genome size and capsid type.Icosahedral capsids are measured by diameter, whereas helical and complex are measured by length and diameter. Viruses differ in capsid size in a spectrum from 10 to more than 1000 nm. The smallest viruses are ssRNA viruses like
Viral evolution
Viral abundance
Viruses are the most abundant biological entities, there are 10^31 viruses on our planet.[23][24] Viruses are capable of infecting all organisms on earth and they are able to survive in much harsher environments, than any cellular life form. As viruses can not be included in the tree of life there is no separate structure illustrating viral diversity and evolutionary relationships.[25] However, viral ubiquity can be imagined as a virosphere covering the whole tree of life.[citation needed]
Nowadays we are entering the phase of exponential viral discovery. The
See also
- virus
- virology
- Virome
- viral evolution
- virus classification
- list of virus families
- list of virus genera
- list of virus species
References
- ^ "World Wide Words: Virosphere". World Wide Words. Retrieved 2023-04-13.
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