Pithovirus sibericum
Classification
Viruses; dsDNA viruses, no RNA stage; unclassified dsDNA viruses.(Source: [1])
Species
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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 March of 2014. The sedimentary layer from which the Pithovirus was isolated dates back 30,000 years or more. Pithovirus infects the Acanthamoeba; human and animal pathogenicity has been ruled out thus far. Pithovirus is notable due to its unprecedented size compared to known viruses and its unusually small genome relative to its size. It cannot be classified with any known virus family.
Genome Structure
Pithovirus sibericum’s genome is unexpectedly different from that of Pandoravirus given their morphological similarity. Pithovirus has an AT-rich genome with a mere 610,033 bp compared to Pandoravirus’s GC-rich, 2.8 Mb genome and encodes only 467 proteins compared to Pandoravirus’s 2,500. Pithovirus’s genome overall structure is currently uncertain, but appears to be either linear with terminal redundancy or circular, in contrast to Pandoravirus’s linear chromosome featuring terminal repeats.
Examination of Pithovirus’s protein-coding genes shows that 67% have no homologs in any known sequence. Of the 33% that are homologous to known proteins, they 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 Marseilleviridiae.
Cell Structure, Metabolism and Life Cycle
The Pithovirus is an oblong rod with a “cork” at its apex that is lost from the virus during replication. The virus features an external envelope and an internal lipid membrane. Within the internal membrane a tubular structure of unknown function has been observed.
Pithovirus infects amoeboid cells by expelling its cork and fusing its internal lipid membrane to the host cell membrane, allowing the virus to establish a virion assembly within the host cell cytoplasm. Once virion assembly is complete, the virus is released via host cell lysis.
Ecology and Pathogenesis
Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
References
Author
Page authored by Jennifer Gliessman, student of Prof. Jay Lennon at IndianaUniversity.
