Pithovirus sibericum: Difference between revisions
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==Cell Structure, Metabolism and Life Cycle== | ==Cell Structure, Metabolism and Life Cycle== | ||
The ''Pithovirus'' is an oblong rod with a “cork” at its apex | The ''Pithovirus'' particle is so far the largest viral particle known. It is an oblong rod, approximately 1.5 micrometers in length and 500nm in diameter, with a “cork” at its apex unique to this unclassified virus. The virus is encased in an external envelope and an internal lipid membrane. Within the internal membrane a tubular structure of unknown function has been observed. The cork at the apex is connected to a coil of membrane within the viral internal membrane. | ||
''Pithovirus'' infects amoeboid cells by expelling its cork and fusing its internal lipid membrane to the host cell membrane, allowing the virus to establish virion assembly machinery within the host cell cytoplasm. Once virion assembly is complete, the virus is released via host cell lysis. | |||
==Ecology and Pathogenesis== | ==Ecology and Pathogenesis== |
Revision as of 13:52, 28 April 2014
Classification
Viruses; dsDNA viruses, no RNA stage; unclassified dsDNA viruses.(Source: [1])
Species
NCBI: Taxonomy |
Pithovirus Sibericum
Description and Significance
Pithovirus sibericum is a giant DNA virus of a previously unclassified family isolated from a layer of permafrost in the Kolyma Lowland region of Siberia in 2013. The sedimentary layer from which the Pithovirus was isolated dates back 30,000 years or more. Pithovirus infects the amoebae; human and animal pathogenicity has been ruled out thus far. Pithovirus is notable due to its unprecedented size compared to known viruses, its unusually small genome relative to its size, and its lack of phylogenetic relationship to any known virus family.
Genome Structure
Pithovirus sibericum’s genome is unexpectedly different from that of other giant DNA viruses with morphological similarity. Pandoravirus, another recently discovered giant DNA virus, has the same amphora morphology and sports a large, GC-rich, 1.26 Mb genome with an estimated 2,500 protein-coding genes. By contrast, Pithovirus has an AT-rich genome with only 610,033 bp and encodes 467 proteins. Paradoxically, the giant DNA viruses with which Pithovirus shares the most genomic attributes and replication methods are morphologically dissimilar icosahedrons. Pithovirus’s genome overall structure is currently uncertain, but appears to be either linear with terminal redundancy or circular.
Examination of Pithovirus’s 467 protein-coding genes indicates that 67% have no homologs in any known sequence. The 33% that code for homologous proteins are equally comparable to viruses, bacteria, and eukaryotic organisms, indicating that Pithovirus has no particularly close phylogenetic relationship to any known sequenced organism. 11% of the total genome corresponds to proteins sequenced from viruses. Phylogenetic analysis places Pithovirus in a clade of icosahedral large DNA virus families and most closely related to Marseilleviridae; notably, this lack of close phylogenetic relationship confirms that Pithovirus belongs to a previously unclassified family of viruses.
The Pithovirus genome lacks genes encoding machinery associated with translation, ATP synthesis, and cell division, which confirmed that it is indeed a virus; furthermore, lack of translation machinery is consistent with cytoplasmic replication. About 21% of its genome contains a non-coding repeat that appears unique to Pithovirus as it is unrelated to repeats found in other viral genomes. Its occurrence results in a relatively low coding density compared to other viral genomes. Of the protein-coding genes, most are associated with nucleotide synthesis and DNA transcription, replication, and repair, which is a typical attribute of a large DNA virus genome.
Cell Structure, Metabolism and Life Cycle
The Pithovirus particle is so far the largest viral particle known. It is an oblong rod, approximately 1.5 micrometers in length and 500nm in diameter, with a “cork” at its apex unique to this unclassified virus. The virus is encased in an external envelope and an internal lipid membrane. Within the internal membrane a tubular structure of unknown function has been observed. The cork at the apex is connected to a coil of membrane within the viral internal membrane.
Pithovirus infects amoeboid cells by expelling its cork and fusing its internal lipid membrane to the host cell membrane, allowing the virus to establish virion assembly machinery within the host cell cytoplasm. Once virion assembly is complete, the virus is released via host cell lysis.
Ecology and Pathogenesis
Pithovirus sibericum is a pathogen of amoeba and proved virulent after 30,000 years frozen in permafrost. This discovery of a millenia-old pathogen has important implications on the effects of human activity to soils and sediments. Furthermore, climate change has the potential to alter icy ecosystems and release previously unknown microorganisms. The possibility that ancient microbes are revived upon release from soil highlights the importance of attending to potential pathogenicity.
References
Author
Page authored by Jennifer Gliessman, student of Prof. Jay Lennon at IndianaUniversity.